ORCID Profile
0000-0002-8801-8656
Current Organisation
University of Sydney
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Publisher: Springer Science and Business Media LLC
Date: 08-1986
DOI: 10.1007/BF01730096
Publisher: Elsevier BV
Date: 2010
DOI: 10.1016/J.JDENT.2009.09.002
Abstract: To characterize molar-incisor hypomineralisation (MIH) defects of different severities quantitatively and qualitatively using X-ray microtomography (XMT) and to measure the range of reduction in mineral density (MD) of MIH enamel compared with the normal range. Ten sound teeth and ten MIH teeth were scanned using a commercial XMT system. Four hydroxyapatite phantoms of different densities were used as calibration standards with each scan. A calibration equation derived from the phantoms with each tooth was used for MD calibration. MD was traced from the cementum-enamel junction (CEJ) to the cusp tip and from the dentine-enamel junction (DEJ) to the outer enamel surface. In sound teeth, MD increased from CEJ to cusp/incisal tip, while in MIH teeth MD dropped from the CEJ to the occlusal region, then increased again at the cusp tip. MD was highest midway between DEJ and outer enamel in sound teeth. In MIH, enamel showed normal thickness and MD was highest near the DEJ and then decreased towards the outer enamel. MD of MIH enamel was on average about 19% lower than sound enamel. The MIH defects seemed to follow the incremental lines of enamel formation. MIH defects are hypomineralised defects of different severities that follow the natural incremental lines of enamel formation. Cuspal areas are usually only mildly affected and cervical enamel always appears to be sound.
Publisher: Walter de Gruyter GmbH
Date: 07-2003
DOI: 10.3139/146.030819
Publisher: Springer Science and Business Media LLC
Date: 15-08-2007
DOI: 10.1007/S12024-007-0029-Y
Abstract: Knowledge of the biomechanical dynamics of blunt force trauma is indispensable for forensic reconstruction of a wounding event. In this study, we describe and interpret wound features on a synthetic skin model under defined laboratory conditions. To simulate skin and the sub-dermal tissues we used open-celled polyurethane sponge (foam), covered by a silicone layer. A drop tube device with three tube lengths (300, 400, and 500 mm), each secured to a weighted steel scaffold and into which a round, 5-kg Federal dumbbell of length 180 mm and diameter 8 cm was placed delivered blows of known impact. To calculate energy and velocity at impact the experimental set-up was replicated using rigid-body dynamics and motion simulation software. We soaked each foam square in 500 mL water, until fully saturated, immediately before placing it beneath the drop tube. We then recorded and classified both external and internal lacerations. The association between external wounding rates and the explanatory variables sponge type, sponge thickness, and height were investigated using Poisson regression. Tears (lacerations) of the silicone skin layer resembled linear lacerations seen in the clinical literature and resulted from only 48.6% of impacts. Poisson regression showed there was no significant difference between the rate of external wounding for different sponge types (P = 0.294) or different drop heights (P = 0.276). Most impacts produced "internal wounds" or subsurface cavitation (96%). There were four internal "wound" types Y-shape (53%), linear (25%), stellate (16%), and double crescent (6%). The two-way interaction height by sponge type was statistically significant in the analysis of variance model (P = 0.035). The other two-way interactions height by thickness and sponge type by thickness, were also bordering on statistical significance (P = 0.061 and P = 0.071, respectively). The observation that external wounds were present for less than half of impacts only, but that nearly all impacts resulted in internal wounds, might explain the observed haematoma formation and contusions so often associated with blunt-force injuries. Our study also confirms the key role of hydrodynamic pressure changes in the actual tearing of subcutaneous tissue. At the moment and site of impact, transferred kinetic energy creates a region of high pressure on the fluid inside the tissue. As a result of the incompressibility of the fluid, this will be displaced away from the impact at a rate that depends on the velocity (or kinetic energy) of impact and the permeability and stiffness of the polymeric foam and skin layer.
Publisher: Elsevier BV
Date: 2007
DOI: 10.1016/J.MEHY.2006.11.048
Abstract: One of the most fundamental yet unanswered questions of human evolution is that of the development of the chin. Whereas it is known that the chin, or mentum osseum, is an unique anatomical feature of modern humans that emerged during the Middle and Late Pleistocene, its origin and biomechanical significance are the subjects of intense controversy. Theories range from the suggestion that the chin evolved as a result of progressive reduction of the dental arch, which left it as a protrusion, to the hypothesis that it provided resistance to mandibular bending during mastication. Until now however, no accepted functional explanation of the human chin has emerged. Here, we develop the hypothesis that the actions of the tongue and non-masticatory orofacial muscles may have played a significant role on the development of the human chin. We report numerical simulations of the forces and resultant stresses developed in hypothetical chinned and non-chinned mandibles. Using empirical data and estimates of the forces generated by the human tongue during speech, our hypothesis suggests that the chin might in fact have developed as a result of the actions of the tongue and perioral muscles, rather than as a buttress to withstand masticatory induced stress. This provides a new perspective on the generation of the chin and importantly, suggests that its appearance may be causally related to the development of the human language.
Publisher: Wiley
Date: 21-05-2004
DOI: 10.1002/JBM.B.30066
Abstract: Empress 1 and Empress 2 are well-known pressable all-ceramic dental materials that have generated substantial interest for many clinicians and patients. These two materials are reputed to benefit from heat pressing during the laboratory fabrication procedures, leading to better crystal distribution within a glass matrix, and hence an improved strength. The present study aimed to evaluate the effect of heat pressing on fracture toughness, microstructural features, and porosity. Results showed that Empress 1 had similar fracture toughness values before the pressing procedure, after it, and after the repressing procedure. The microstructural features were also similar among these specimens, but a more uniform distribution of leucite crystals was observed following the pressing and repressing procedures. Empress 2 demonstrated two different fracture toughness values. This was associated with the alignment of lithium disilicate crystals that occurred after the pressing and repressing procedures, which led to different indentation induced crack lengths, depending upon whether cracks propagated parallel to or perpendicular to the aligned crystals, the former having lower toughness than those that propagated in the perpendicular direction. Porosity, in terms of both the size and number of pores, was found to decrease after the pressing and repressing procedures for both materials. Repressing resulted in significant growth of the lithium disilicate crystals in Empress 2, but there was no change for the leucite crystals in Empress 1. The change in the lithium disilicate crystals' size did not have a noticeable effect on the fracture toughness of Empress 2. It was concluded that heat pressing did not significantly affect the fracture toughness of Empress 1, but resulted in two different values for Empress 2. It also decreased the size and number of pores for both materials, which could contribute to the strength improvement found after heat pressing, which has been reported in previous studies.
Publisher: Elsevier BV
Date: 08-2010
DOI: 10.1016/J.JDENT.2010.05.003
Abstract: This study evaluated the effect of a chromium interlayer deposited by electroplating on the adhesion between titanium and porcelain by means of strain energy release rate (G-value (J/m(2)) or interfacial toughness). Seventy rectangular specimens of commercially pure titanium (CP Ti) plates grade II (8 mm x 30 mm x 1.5 mm) were prepared. The specimens were ided into seven groups according to the electroplating treatment Gr 1 (control without electroplating, n=10) Gr 2 (5% (w/v) chromium nitrate solution for 30 min, n=10) Gr 3 (5% (w/v) chromium nitrate solution for 60 min, n=10) Gr 4 (5% (w/v) chromium nitrate solution for 120 min, n=10) Gr 5 (10% (w/v) chromium nitrate solution for 30 min, n=10) and Gr 6 (10% (w/v) chromium nitrate solution for 60 min, n=10) and Gr 7 (10% (w/v) chromium nitrate solution for 120 min, n=10). Each group was further equally ided into two subgroups according to the type of porcelain used. Two titanium-porcelains (Vita Titankeramik and Triceram) were applied to each subgroup (n=5). The G-value was measured with a four-point bending configuration. Following fracture testing, specimens were examined with a scanning electron microscope (SEM). Data were analysed using ANOVA and Tukey's test. Adhesion values were significantly affected by the type of electroplating treatment (P<0.05) and by the type of porcelain (P<0.05). The CP Ti/Vita Titankeramik (0.5h 5% (w/v), 1h 5% (w/v) and 0.5h 10% (w/v)) groups showed the highest G-value (36.94+/-3.25, 38.87+/-7.91 and 37.22+/-5.76J/m(2)) amongst their groups. The CP Ti/Triceram (0.5h 5% (w/v) and 0.5h 10% (w/v)) groups (26.72+/-4.36 and 26.94+/-3.52J/m(2)) were statistically significantly different from the control group (14.99+/-1.50J/m(2)) (P<0.05). A definitive relationship was found between Cr film thickness and G-value for both porcelain materials. Adhesion between porcelain and CP Ti can be improved by the use of chromium interlayer prior to porcelain firing.
Publisher: Wiley
Date: 07-1992
Publisher: Elsevier BV
Date: 10-2014
DOI: 10.1016/J.JMBBM.2014.06.008
Abstract: It has been widely shown that proteoglycans (PG) and their glycosaminoglycan (GAG) side-chains form supramolecular aggregates that interconnect the collagenous network in connective tissues and play a significant role in regulating the mechanical behavior of the extracellular matrix, particularly in soft tissues. However, collective evidence of the mechanical participation of PGs and GAGs in mineralized tissues remains poorly explored in the literature. Here, we address this knowledge gap and discuss the participation of PGs on the biomechanics of mineralized tissues including dentine, cementum and bone. We review evidence suggesting that, on a microscale, PGs regulate the hydrostatic and osmotic pressure, as well as the poroelastic behavior of dentine and bone. On the nanoscale, we review the so-called sliding filament theory and intramolecular stretching of GAGs. We also discuss recent interpretations whereby folding and unfolding of the PG protein core, potentially in association with SIBLING proteins, may be a contributing factor to the mechanical behavior of mineralized tissues. Finally, we review in vitro and in vivo studies of mineralized tissues with targeted disruption or digestion of specific PG family members, which provide further insights into their relevance to the mechanical properties of load bearing hard tissues. In summary, this review brings forth collective evidence suggesting that PGs and GAGs, although less than 5% of the tissue matrix, may play a role in the mechanical behavior and durability of mineralized tissues.
Publisher: Elsevier BV
Date: 05-1985
Publisher: Springer Science and Business Media LLC
Date: 2013
Publisher: Springer Science and Business Media LLC
Date: 09-1997
Abstract: Elastic modulus of thin homogeneous films can be determined by indenting the specimen to various depths and extrapolating the measured (apparent) E -values to zero penetration. The paper shows the application of five approximation functions for this purpose: linear, exponential, reciprocal exponential, Gao's, and the Doerner and Nix functions. Comparison of the results for 26 film/substrate combinations has shown that the indentation response of film/substrate composites can, in general, be described by the Gao analytical function. In determining the thin film modulus from experimental data, satisfactory results can also be obtained with the exponential function, while linear function may be used only for thick films where the relative depths of penetration are small. The article explains the pertinent procedures and gives practical recommendations for the testing.
Publisher: Elsevier BV
Date: 06-2009
DOI: 10.1016/J.AJODO.2007.06.015
Abstract: This in-vitro study investigated the loads (forces), moments, and moment-to-force ratios (M:F) generated during the activation and deactivation of T closing loops made of rectangular nickel-titanium (NiTi) and titanium-molybdenum alloy (TMA) wires incorporating either 0 degrees, 15 degrees, or 30 degrees of preactivation. T-loop designs were formed in the wires by using a standard template, and, for the NiTi alloys, a temperature of 510 degrees C for 9 minutes was used. Forces and moments of the T-loops were measured at 35.6 degrees C +/- 0.5 degrees C, and these were used to calculate the M:F ratio. Analysis of covariance was used to identify statistical differences between wire alloy and preactivation. Nonpreactivated (0 degrees) closing loops failed to produce an optimum M:F ratio for translational tooth movement. With increasing preactivation, the M:F ratio increased over the deactivation range for both alloys. The NiTi T-loops produced an M:F ratio of greater than 10:1 over a larger deactivation range (while still delivering a force of 50-150 g) than for the equivalent TMA T-loop. The difference in M:F between the 0 degrees and 30 degrees TMA loops was statistically significant (P <0.000) but not between the equivalent NiTi loops (P <0.136). There was no statistical difference between the NiTi wire alloys at any preactivation angulation. Optimum M:F ratios for orthodontic translation can be achieved by using preactivated NiTi and TMA T-loops, with NiTi loops maintaining the optimum M:F ratio over a greater range of deactivation.
Publisher: Elsevier BV
Date: 2016
DOI: 10.1016/J.JMBBM.2015.08.010
Abstract: The principle of minimal intervention dentistry (MID) is to limit removal of carious tooth tissue while maximizing its repair and survival potential. The objective of this study is to explore the fracture resistance of a permanent molar tooth with a fissure carious lesion along with three clinical restoration procedures, namely one traditional and two conservative approaches, based upon MID. The traditional restoration employs extensive surgical removal of enamel and dentine about the cavity to eliminate potential risk of further caries development, while conservative method #1 removes significantly less enamel and infected dentine, and conservative method #2 only restores the overhanging enamel above the cavity and leaves the infected and affected dentine as it was. An extended finite element method (XFEM) is adopted here to analyze the fracture behaviors of both two-dimensional (2D) and three-dimensional (3D) modeling of these four different scenarios. It was found that the two conservative methods exhibited better fracture resistance than the traditional restorative method. Although conservative method #2 has less fracture resistance than method #1, it had significantly superior fracture resistance compared to other restorations. More important, after cavity sealing it may potentially enhance the opportunity for remineralization and improved loading bearing capacity and fracture resistance.
Publisher: Elsevier BV
Date: 11-2013
DOI: 10.1016/J.DENTAL.2013.08.204
Abstract: To investigate the effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain. The strain energy release rate using a four-point bending stable fracture test was evaluated for two different porcelains [leucite containing (VM9) and glass (Zirox) porcelain] veneered to zirconia. Prior to veneering the zirconia had been subjected to 0 (control), 1, 5, 10 and 20 autoclave cycles. The specimens were manufactured to a total bi-layer dimension of 30 mm × 8 mm × 3 mm. Subsequent scanning electron microscopy/energy dispersive spectrometry, electron backscatter diffraction and X-ray diffraction analysis were performed to identify the phase transformation and fracture behavior. The strain energy release rate for debonding of the VM9 specimens were significantly higher (p<0.05) compared to the Zirox specimens across all test groups. Increasing autoclave cycles lowered the strain energy release rate significantly (p<0.05) from 18.67 J/m(2) (control) to the lowest of 12.79 J/m(2) (cycle 10) for only the VM9 specimens. SEM analyses showed predominant cohesive fracture within the porcelain for all cycle groups. XRD analysis of the substrate prior to veneering confirmed a tetragonal to monoclinic phase transformation with increasing the number of autoclave cycles between 5 and 20. The monoclinic phase reverted back to tetragonal phase after undergoing conventional porcelain firing cycles. EBSD data showed significant changes of the grain size distribution between the control and autoclaved specimen (cycle 20). Increasing autoclave cycles only significantly decreased the adhesion of the VM9 layered specimens. In addition, a conventional porcelain firing schedule completely reverted the monoclinic phase back to tetragonal.
Publisher: Elsevier BV
Date: 11-1975
Publisher: Elsevier BV
Date: 09-2004
Publisher: Informa UK Limited
Date: 11-1996
Publisher: Wiley
Date: 07-1989
Publisher: Elsevier BV
Date: 08-2001
Abstract: Cementum is a nonuniform connective tissue that covers the roots of human teeth. Investigation of the physical properties of cementum may help in understanding or evaluating any possible connection to root resorption. A variety of engineering tests are available to investigate these properties. However, the thickness of the cementum layer varies, and this limits the applicability of these techniques in determining the physical properties of cementum. Hardness testing with Knoop and Vickers indentations overcame some of these limitations, but they prohibited the retrieval and retesting of the s le and therefore the testing was restricted to one area or section of the tooth. Another limiting factor with the existing techniques was the risk of artifacts related to the embedding material such as acrylic. A new method to investigate the physical properties of human premolar cementum was developed to obtain a 3-dimensional map of these properties with the Ultra Micro Indentation System (UMIS-2000 Commonwealth Scientific and Industrial Research Organization, C bell, Australia). UMIS-2000 is a nano-indentation instrument for investigation of the properties of the near-surface region of materials. Premolars were harvested from orthodontic patients requiring extractions and then mounted on a newly designed surveyor that allowed s le retrieval and 3-dimensional rotation. This novel method enabled the quantitative testing of root surface cementum, on all 4 root surfaces, extending from the apex to the cementoenamel junction at 60 different sites.
Publisher: Springer Science and Business Media LLC
Date: 07-1985
DOI: 10.1007/BF00720520
Publisher: Wiley
Date: 22-11-2004
DOI: 10.1111/J.1600-0722.2004.00162.X
Abstract: The aims of the present study were to investigate the mechanical properties of first permanent molars affected with enamel hypomineralization or hypoplasia, and to describe the appearance of these lesions under scanning electron microscopy. Eight first permanent molar test teeth and two unaffected premolars (controls) were enclosed in resin, then sectioned axially and polished. The hardness and modulus of elasticity was determined from a single array of indentations made parallel to the amelo-dentinal junction using an Ultra-Micro-Indentation system. The teeth were then examined using the scanning electron microscope. The mechanical properties of the test teeth in the unaffected cervical region (hardness and modulus range, 2.03-4.99 GPa and 50.39-96.87 GPa, respectively) were similar to those of the control enamel (hardness and modulus range, 2.71-4.15 GPa and 62.06-95.77 GPa, respectively). Between the unaffected cervical enamel and the hypomineralized region there was a transitional area of 500-600 microm where the mechanical properties in the experimental teeth decreased linearly. The mechanical properties of the hypomineralized region of each experimental tooth were significantly lower than those of the control or cervical regions (hardness and modulus range, 0.07-1.74 GPa and 3.26-40.96 GPa, respectively). The scanning electron microscopy views revealed disorganized enamel with poorly demarcated prism boundaries in the affected regions. In conclusion, the hardness and modulus of elasticity of hypomineralized enamel in first permanent molars is significantly less than in unaffected areas of the same tooth. The reason for this is unclear but may be related to the lack of organization of the enamel crystals.
Publisher: Springer Science and Business Media LLC
Date: 11-09-2007
DOI: 10.1007/S00216-007-1520-8
Abstract: The objective of this research was to investigate nanoindentation-induced residual stresses in human enamel using Raman microspectroscopy and establish if this approach can be used as a stress meter. Healthy human premolars and sintered hydroxyapatite s les were embedded, cut, and the surfaces were polished finely with a 0.05 microm polishing paste before Berkovich and spherical indentations were made with a force of 100 mN. Spectra were collected using a Renishaw Raman InVia reflex microscope equipped with an air-cooled charge-coupled device (CCD) camera. S le excitation was achieved using either an argon ion laser emitting at 514.5-nm or a NIR diode laser emitting at 830-nm. The residual micro stresses within and surrounding the indentation impressions were monitored by mapping the position of the nu(1)(PO(4)) band of (crystalline) hydroxyapatite. The Raman maps coincided well with the optical micrographs of the s les. Despite the presence of a fluorescence background from the organic component of human enamel, spectra collected using 514.5-nm excitation exhibited more significant shifts in the position of the nu(1)(PO(4)) band than spectra collected using 830-nm excitation. This implies that the former excitation may be a more appropriate excitation for stress detection. It was concluded that Raman microspectroscopy provides a novel high-resolution and non-destructive method for exploring the role of microstructure on the residual stress distribution within natural biocomposites.
Publisher: Elsevier BV
Date: 08-2015
DOI: 10.1016/J.DENTAL.2015.05.007
Abstract: The Schwickerath three point bending adhesion test is the basis of the International Standard ISO 9693:1999 procedure for assessing porcelain bonding to metals [1]. It has also been used to evaluate the adhesion of porcelain to zirconia. The purpose of this paper is a fracture mechanics analysis of this test, which allows determination of the crack-length load-displacement and toughness dependence of cracks extending along or near the interface. Linear elastic mechanics is used to develop expressions for the strain energy and compliance of Schwickerath geometry specimens as a function of crack extension along or near the interface. From the derivative of the compliance as a function of crack growth the strain energy release rate (G, N/m) is determined. The energy release rate for interface crack extension of Schwickerath geometry specimens is determined. It is found that a simple relationship between the minima of the force-displacement response and the strain energy release rate G exists. Further development enables the predicted force-displacement response as a function of crack length to be derived for different values of G. Experimental results of porcelain bonded to zirconia with and without notches of various lengths machined along the interface verify the expressions and analysis developed. With the fracture mechanics analysis developed in this paper it is possible to determine the quality of adhesion in Schwickerath specimens by the interface toughness in addition to the nominal interface shear bond strength. As the toughness of brittle materials has much less scatter than its strength, the interface toughness characterization of the adhesion should allow for a better distinction between the adhesion quality of bonding.
Publisher: Wiley
Date: 03-1992
Publisher: Informa UK Limited
Date: 07-2002
Publisher: Elsevier BV
Date: 11-1998
Publisher: Elsevier BV
Date: 1993
Publisher: Elsevier BV
Date: 11-1998
Publisher: Elsevier BV
Date: 10-1997
Publisher: Springer Science and Business Media LLC
Date: 11-2007
Abstract: Detailed cyclic indentation experiments of crystalline silicon in this study show interesting behavior depending on the end phase from the previous cycle. To enable the behavior of these phases to be studied on reloading, the cyclic indentation response of the material is examined under conditions where the pressure-induced Si-II phase transforms either to amorphous (a-Si) or high pressure Si-XII/Si-III phases on unloading. For an amorphous end phase the subsequent reloading is hysteretic, and for high pressure crystalline end phases it is elastic. This indicates that, whereas a-Si re-transforms readily to Si-II upon reloading, Si-XII/Si-III does not retransform to Si-II even at the maximum indentation load. Based on the concept of the effective indenter shape and stresses induced in the material, we show that Si-XII/Si-III has a greater critical hydrostatic pressure for retransformation to Si-II than that of the diamond cubic Si-I.
Publisher: Elsevier BV
Date: 12-1994
Publisher: Springer Science and Business Media LLC
Date: 04-1985
DOI: 10.1007/BF00719752
Publisher: Wiley
Date: 21-05-2010
DOI: 10.1111/J.1834-7819.2010.01214.X
Abstract: The effect of cavity design is a controversial and underrated factor in the clinical success of ceramic inlays and inlay supported prosthesis. Many articles and studies have been conducted into the advantages and disadvantages of isolated aspects of preparation design, but lacking is a review of the most relevant papers which bring together a consensus on all the critical features. Hence, a review and analysis of cavity depth, width, preparation taper and internal line angles is warranted in our attempts to formulate preparation guidelines that will lead to clinically successful, all-ceramic inlay restorations and ceramic inlay supported prosthesis.
Publisher: Springer Science and Business Media LLC
Date: 1995
DOI: 10.1007/BF02226979
Publisher: Wiley
Date: 03-1990
Publisher: Springer Science and Business Media LLC
Date: 12-1976
DOI: 10.1007/BF00752103
Publisher: Informa UK Limited
Date: 1994
Publisher: Wiley
Date: 1989
Publisher: Elsevier BV
Date: 10-2007
DOI: 10.1016/J.BIOMATERIALS.2007.06.020
Abstract: To investigate the role of different environments in regulating the mechanical behaviour of mature human enamel. Healthy enamel s les were subjected to different environmental treatments such as ethanol dehydration, water re-hydration, desiccation at room temperature, and after heating (burnt) to 300 degrees C. Nanoindentation tests were done on all s les for determination of elastic modulus, hardness and indentation creep behaviour. Scanning electron microscopy (SEM) was used to observe surfaces and indentation impressions of different treated s les. Statistically significant differences of the mechanical properties were found following the various treatments. Burnt s le had the highest elastic modulus and hardness of approximately 115 and approximately 6 GPa, respectively, while the re-hydrated s le showed the lowest values of approximately 95 and approximately 4 GPa. The creep deformation showed the inverse response to the environment-induced elastic modulus results with negligible creep found for the burnt specimens. SEM showed that, although no significant structural changes were found for burnt s les after heating, there was much more cracking about the residual indentation impression. Because of the chemical and thermal stability of hydroxyapatite under the experimental conditions investigated, differences of mechanical behaviour of enamel are rationalized in terms of changes to the matrix proteins and loss of water within enamel. These results indicate that matrix proteins play an important role in regulating the mechanical behaviour of enamel as a biocomposite.
Publisher: Trans Tech Publications, Ltd.
Date: 07-2011
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.268-270.853
Abstract: Bioceramics have rapidly emerged as one of major biomaterials in modern biomedical applications because of its outstanding biocompatibility. However, one drawback is its low tensile strength and fracture toughness due to brittleness and inherent microstructural defects, which to a certain extent prevents the ceramics from fully replacing metals used as load-bearing prostheses. This paper aims to model the crack initiation and propagation in ceramic fixed partial denture, namely dental bridge, by using two recently developed methods namely continuum-to-discrete element method (CDEM) in ELFEN and extended finite element methods (XFEM) in ABAQUS. Unlike most existing studies that typically required prescriptions of initial cracks, these two new approaches will model crack initiation and propagation automatically. They are applied to a typical prosthodontic ex le, thereby demonstrating their applicability and effectiveness in biomedical applications.
Publisher: AIP Publishing
Date: 21-05-2001
DOI: 10.1063/1.1372207
Abstract: The mechanical deformation by spherical indentation of both crystalline InP and GaAs was characterized using cross-sectional transmission electron microscopy (XTEM) and atomic force microscopy. All load–unload curves show a discontinuity (or “pop in”) during loading. Slip bands oriented along {111} planes are visible in XTEM micrographs from residual indentations in both materials and no evidence of any phase transformations was found. Higher load indentations (35 mN for InP and 50 mN for GaAs) also revealed subsurface cracking. In contrast no cracking was found beneath a 25 mN InP indent although the hardness and modulus data are almost identical to those of the cracked s le. The subsurface cracks are thought to be nucleated by high stress concentrations caused by dislocation pileup.
Publisher: SAGE Publications
Date: 07-2006
DOI: 10.1177/154405910608500711
Abstract: The development of the chin, a feature unique to humans, suggests a close functional linkage between jaw biomechanics and symphyseal architecture. The present study tests the hypothesis that the presence of a chin changes strain patterns in the loaded mandible. Using an anatomically correct 3-D model of a dentate mandible derived from a CT scan image, we analyzed strain patterns during incisal and molar biting. We then constructed a second mandible, without a chin, by ‘defeaturing’ the first model. Strain patterns of the second model were then compared and contrasted to the first. Our main finding was that chinned and non-chinned mandibles follow closely concordant patterns of strain distribution. The results suggest that the development of the human chin is unrelated to the demands placed on the mandible during function.
Publisher: Springer Science and Business Media LLC
Date: 02-1974
DOI: 10.1007/BF00550939
Publisher: Springer Science and Business Media LLC
Date: 30-06-2015
DOI: 10.1557/JMR.2015.178
Publisher: American Chemical Society (ACS)
Date: 27-09-2016
Abstract: The common tensile lap-shear test for adhesive joints is inappropriate for brittle substrates such as glasses or ceramics where stress intensifications due to cl ing and additional bending moments invalidate results. Nevertheless, bonding of glasses and ceramics is still important in display applications for electronics, in safety glass and ballistic armor, for dental braces and restoratives, or in recently developed bioinspired composites. To mechanically characterize adhesive bondings in these fields nonetheless, a novel approach based on the so-called Schwickerath test for dental sintered joints is used. This new method not only matches data from conventional analysis but also uniquely combines the accurate determination of interfacial shear strength and toughness in one simple test. The approach is verified for sapphire-epoxy joints that are of interest for bioinspired composites. For these, the procedure not only provides quantitative interfacial properties for the first time, it also exemplarily suggests annealing of sapphire at 1000 °C for 10 h for mechanically and economically effective improvements of the interfacial bond strength and toughness. With increases of strength and toughness from approximately 8 to 29 MPa and from 2.6 to 35 J/m
Publisher: Springer Science and Business Media LLC
Date: 2013
Publisher: The Royal Society
Date: 08-2015
Abstract: The prevalence of prosthodontic treatment has been well recognized, and the need is continuously increasing with the ageing population. While the oral mucosa plays a critical role in the treatment outcome, the associated biomechanics is not yet fully understood. Using the literature available, this paper provides a critical review on four aspects of mucosal biomechanics, including static, dynamic, volumetric and interactive responses, which are interpreted by its elasticity, viscosity ermeability, apparent Poisson's ratio and friction coefficient, respectively. Both empirical studies and numerical models are analysed and compared to gain anatomical and physiological insights. Furthermore, the clinical applications of such biomechanical knowledge on the mucosa are explored to address some critical concerns, including stimuli for tissue remodelling (interstitial hydrostatic pressure), pressure–pain thresholds, tissue displaceability and residual bone resorption. Through this review, the state of the art in mucosal biomechanics and their clinical implications are discussed for future research interests, including clinical applications, computational modelling, design optimization and prosthetic fabrication.
Publisher: Elsevier BV
Date: 04-2017
DOI: 10.1016/J.DENTAL.2017.01.009
Abstract: To investigate and characterize the distribution of fabrication defects in bilayered lithium disilicate glass-ceramic (LDG) crowns using micro-CT and 3D reconstruction. Ten standardized molar crowns (IPS e.max Press Ivoclar Vivadent) were fabricated by heat-pressing on a core and subsequent manual veneering. All crowns were scanned by micro-CT and 3D reconstructed. Volume, position and sphericity of each defect was measured in every crown. Each crown was ided into four regions-central fossa (CF), occlusal fossa (OF), cusp (C) and axial wall (AW). Porosity and number density of each region were calculated. Statistical analyses were performed using Welch two s le t-test, Friedman one-way rank sum test and Nemenyi post-hoc test. The defect volume distribution type was determined based on Akaike information criterion (AIC). The core ceramic contained fewer defects (p<0.001) than the veneer layer. The size of smaller defects, which were 95% of the total, obeyed a logarithmic normal distribution. Region CF showed higher porosity (p<0.001) than the other regions. Defect number density of region CF was higher than region C (p 0.05). Four of ten specimens contained the largest pores in region CF, while for the remaining six specimens the largest pore was in region OF. LDG core ceramic contained fewer defects than the veneer ceramic. LDG strength estimated from pore size was comparable to literature values. Large defects were more likely to appear at the core-veneer interface of occlusal fossa, while small defects also distributed in every region of the crowns but tended to aggregate in the central fossa region. Size distribution of small defects in veneer obeyed a logarithmic normal distribution.
Publisher: Elsevier BV
Date: 1990
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2018
Publisher: Elsevier BV
Date: 03-2016
DOI: 10.1016/J.JDENT.2016.01.012
Abstract: The aim of this study was to characterize the mineral distribution pattern of natural fissural enamel lesions and to quantify structural parameters and mineral density of these lesions in comparison to proximal white spot enamel lesions. Imaging was undertaken using a high-resolution desktop micro-computed tomography system. A calibration equation was used to transform the grey level values of images into true mineral density values. The value of lesion parameters including the mineral density and the thickness of the surface layer of the enamel lesion were extracted from mineral density profiles. The thickness of the surface layer showed variation among different lesions and it ranged from 0-90 μm in proximal lesions and 0-137 μm in fissural lesions. The average thickness of surface layer in fissural lesions was significantly higher than smooth surface proximal lesions. Sound fissural enamel showed lower mineral density compared to proximal enamel. Micro-CT and the suggested de-noising and visualization method provide an efficient high-resolution approach for non-destructive evaluation of fissural lesions. Using these methods, the current study revealed the exclusive pattern and structure of fissural enamel lesions which may provide a basis for future studies on prevention and remineralization of these lesions. The common demineralization pattern of fissural lesions, which indicates the extension of the lesion in two directions towards the pulp horns, may explain the early inflammation and symptoms of the pulp in fissural lesions even when the lesion base appears far from the pulp roof in normal radiographs. In addition, the presence of the surface layer, indicates that vigorous probing of the occlusal fissures may lead to breakage and cavitation of the enamel lesions.
Publisher: Elsevier BV
Date: 2010
DOI: 10.1016/J.JBIOMECH.2009.08.024
Abstract: The ability to assess the effects of an implant on bone remodeling is of particular importance to prosthesis placement planning and associated treatment assurance. Prediction of on-going bone responses will enable us to improve the performance of a restoration. Although the bone remodeling for long bones had been extensively studied, there have been relatively few reports for dental scenarios despite its increasing significance with more and more dental implant placements. This paper aimed to develop a systematic protocol to assess mandibular bone remodeling induced by dental implantation, which extends the remodeling algorithms established for the long bones into dental settings. In this study, a 3D model for a segment of a human mandible was generated from in vivo CT scan images, together with a titanium implant embedded to the mandible. The results examined the changes in bone density and stiffness as a result of bone remodeling over a period of 48 months. Resonance frequency analysis was also performed to relate natural frequencies to bone remodeling. The density contours are qualitatively compared with clinical follow-up X-ray images, thereby providing validity for the bone remodeling algorithm presented in dental bone analysis.
Publisher: Springer Science and Business Media LLC
Date: 2003
Publisher: AIP Publishing
Date: 10-02-2003
DOI: 10.1063/1.1541110
Abstract: This study discusses the behavior of high-pressure phases of monocrystalline silicon when subjected to cyclic indentations with a spherical indenter. It was found that specific phases form in the second and subsequent indentation cycles under low maximum loads. An increase of the maximum indentation load causes changes of subsequent indentation cycles of the phase transformation events to occur earlier on both loading and unloading. The repeated indentations result in the formation of a multiphase structure in the deformed zone, featuring a nonhysteresis behavior. After a critical stage, the properties of the transformed material are stabilized and further indentations can no longer alter the load–displacement curve. It was also found that the greater the maximum load, the faster the occurence of property stabilization.
Publisher: Wiley
Date: 1991
Publisher: Wiley
Date: 04-1987
Publisher: Elsevier BV
Date: 05-1997
Publisher: Elsevier BV
Date: 07-2012
Publisher: Springer Science and Business Media LLC
Date: 12-2004
Abstract: The observation and finite element simulation of Ti–6Al–4V loaded by a spherical indenter were compared. The contact radius at the maximum load was 40% of the indenter radius, which resulted in a high degree of plasticity induced beneath the indenter. The spherical impression profile predicted by the simulation was in agreement with that of the observation. The local curvature of the spherical impression was shown to vary with radial distance. The overall curvature change with radial distance was more distinctive in the presence of static friction. Due to the large plastic zone in the material, neither the Field–Swain nor the Oliver–Pharr method was able to predict the elastic recovery depths in the center of indentation and at the perimeter of contact. The ratio of the two depths predicted by the latter method, however, may be used to verify the applicability of the method itself in determining the elastic modulus of a ductile material.
Publisher: Springer Science and Business Media LLC
Date: 12-2004
Abstract: A simple method has been proposed for an independent determination of the frame compliance C f and the area function of a Berkovich indenter. C f was determined from the unloading compliance of very large indentations in four test materials (fused silica, silicon nitride, high-carbon steel, and copper-zinc alloy) with known elastic properties, following the Oliver–Pharr method by assuming the ideal shape of Berkovich indenter. For a specific value of C f (= 0.3 nm/mN in our case) all the specimens showed an h c (contact depth)-independent modulus, which agreed well with the expected value when the pile-up effect was taken into account. The contact area A ( h c ) was then estimated using fused silica as the standard specimen, according to two different procedures, i.e., the Oliver–Pharr method and the Field–Swain method. Both methods gave almost identical area functions over the whole range of the measurement. It was also found that such area functions can be described by two separate equations: A = 2π R e h c for h c Δ h and A = g ( h c + Δ h ) 2 for h c ⩾ Δ h, where R e is the effective tip radius, Δ h the truncation depth, and g the geometrical factor for a Berkovich indenter. Based on the spherically truncated cone model, a simple procedure is presented to determine all these parameters from the analysis of a multiple partial unloading P-h curve.
Publisher: Elsevier BV
Date: 04-2013
DOI: 10.1016/J.DENTAL.2013.01.002
Abstract: To determine and identify correlations between flexural strength, strain at failure, elastic modulus and hardness versus ceramic network densities of a range of novel polymer-infiltrated-ceramic-network (PICN) materials. Four ceramic network densities ranging from 59% to 72% of theoretical density, resin infiltrated PICN as well as pure polymer and dense ceramic cross-sections were subjected to Vickers Indentations (HV 5) for hardness evaluation. The flexural strength and elastic modulus were measured using three-point-bending. The fracture response of PICNs was determined for cracks induced by Vickers-indentation. Optical and scanning electron microscopy (SEM) was employed to observe the indented areas. Depending on the density of the porous ceramic the flexural strength of PICNs ranged from 131 to 160MPa, the hardness values ranged between 1.05 and 2.10GPa and the elastic modulus between 16.4 and 28.1GPa. SEM observations of the indentation induced cracks indicate that the polymer network causes greater crack deflection than the dense ceramic material. The results were compared with simple analytical expressions for property variation of two phase composite materials. This study points out the correlation between ceramic network density, elastic modulus and hardness of PICNs. These materials are considered to more closely imitate natural tooth properties compared with existing dental restorative materials.
Publisher: Elsevier BV
Date: 12-2010
DOI: 10.1016/J.ACTBIO.2010.06.028
Abstract: Our objectives were to correlate the mineral density (MD) and elastic modulus (E) of natural white spot lesions (WSLs) and compare them with analytical and numerical models. Five natural WSLs from four extracted sound premolar teeth were scanned at a voxel size of 7.6μm using a desktop X-ray microtomography (XRMT) system. Five hydroxyapatite phantoms with densities ranging from 1.52 to 3.14gcm⁻³ were used as calibration standards for each scan. MD throughout the WSLs was quantified using an MD calibration equation derived from hydroxyapatite phantoms. Subsequently, teeth were cross-sectioned and the E modulus was measured systematically across the WSLs at intervals of 25 and 50μm using nanoindentation. The MD and E modulus of WSLs correlated well. The relationship may be expressed as E=E⁰exp(-bP) (R²=0.952) with E⁰ the elastic modulus of the fully dense material, P the porosity and b a constant. The results for sound enamel were compared with Spears model. The limitation of Spears model to the WSLs is discussed and an alternative model developed by Rice for porous materials is proposed. Clinical implications of this work for quantifying de-/remineralization of teeth are pointed out. We conclude that XRMT can be utilized to extrapolate the E modulus of WSLs. This provides a basis for non-destructive, longitudinal analysis of WSLs in de-/remineralization studies of enamel.
Publisher: Wiley
Date: 30-04-2004
DOI: 10.1111/J.1601-6343.2004.00281.X
Abstract: To study the effect of different orthodontic force levels on cementum, investigating from the point of view of its physical properties, alterations in the mineral components, type and location of the resorption craters and the exploration in 3D of space. In vivo human premolars subjected to heavy and light forces were employed for this study. After a period of movement they were analyzed for hardness and elasticity. Also, the mineral composition measuring Ca, P and F of the cementum root surface was investigated. A new method for volumetric analysis of resorption craters was developed. There were no significant differences for hardness and elastic modulus between the light and heavy force groups and no significant effects for different tooth positions. Significant inter-in idual variation in the Ca, P and F concentrations was noted. Force-related data showed that mean volume of the resorption crater in light-force group was 3.49-fold greater than the control group, and the heavy-force group 11.59-fold more than control group. The heavy force group had 3.31-fold greater total resorption volume then light force group. Buccal cervical and lingual apical regions demonstrated significantly more resorption craters than the other regions. The 2D measurements were strongly correlated to 3D measurements. The application of light and heavy forces did not show any statistically significant differences in hardness and elastic modulus when compared with untreated teeth. The inconsistent increase or decrease of Ca, P and F contents between control and experimental teeth at sites of compression and tension were difficult to explain. There was more resorption by volume in the heavy force group as compared with the light group and controls. Our data also suggested that the high-pressure zones might be more susceptible to resorption after 28 days of force application.
Publisher: AIP Publishing
Date: 11-02-2002
DOI: 10.1063/1.1448175
Abstract: The deformation behavior of bulk ZnO single crystals is studied by a combination of spherical nanoindentation and atomic force microscopy. Results show that ZnO exhibits plastic deformation for relatively low loads (≳4–13 mN with an ∼4.2 μm radius spherical indenter). Interestingly, the elastic–plastic deformation transition threshold depends on the loading rate, with faster loading resulting, on average, in larger threshold values. Multiple discontinuities (so called “pop-in” events) in force–displacement curves are observed during indentation loading. No discontinuities are observed on unloading. Slip is identified as the major mode of plastic deformation in ZnO, and pop-in events are attributed to the initiation of slip. An analysis of partial load–unload data reveals values of the hardness and Young’s modulus of 5.0±0.1 and 111.2±4.7 GPa, respectively, for a plastic penetration depth of 300 nm. Physical processes determining deformation behavior of ZnO are discussed.
Publisher: Wiley
Date: 10-07-2011
DOI: 10.1111/J.1834-7819.2011.01341.X
Abstract: The clinical use of all-ceramic crowns and fixed partial dentures has seen widespread adoption over the past few years due to their increasing durability and longevity. However, the application of inlays as an abutment design has not been as readily embraced because of their relatively high failure rates. With the use of an idealized inlay preparation design and prosthesis form which better distributes the tensile stresses, it is possible to utilize the inlay as support for an all-ceramic fixed partial denture. Utilizing a three-dimensional finite element analysis, a direct comparison of the inlay supported all-ceramic bridge against the traditional full crown supported all-ceramic bridge is made. The results demonstrate that peak stresses in the inlay bridge are around 20% higher than in the full crown supported bridge with von Mises peaking at about 730 MPa when subjected to theoretical average maximum bite force in the molar region of 700 N, which is similar to the ultimate tensile strengths of current zirconia based ceramics.
Publisher: SAGE Publications
Date: 06-2004
DOI: 10.1243/095440604774202222
Abstract: This paper studies the difference in the mechanical response of monocrystalline silicon to cyclic microindentations in air and in water. It shows that in air the indentations with a spherical indenter generated consequent phase transformations. In the first indentation cycle, the decomposition featured amorphous phase at low maximum indentation load, Pmax, that was converged to a crystalline compound in repeated indentations. A high Pmax generated crystalline R8/BC8 phases only. After a few cycles, the transformed material behaved linearly elastically, and its properties became stable. However, when the same indentations were conducted in water, the property stabilization process of the transformed material was significantly slowed down, featuring non-linear elasticity. It seemed that at a high Pmax a chemical effect took place in the central part of the transformation zone.
Publisher: Springer Science and Business Media LLC
Date: 1998
Publisher: Wiley
Date: 12-1992
Publisher: SPIE
Date: 25-02-2004
DOI: 10.1117/12.512968
Publisher: American Association for the Advancement of Science (AAAS)
Date: 02-09-2016
Abstract: Atomic-scale study of human dental enamel reveals an intergranular amorphous phase thought to be responsible for tooth decay.
Publisher: Elsevier BV
Date: 04-1979
Publisher: Trans Tech Publications, Ltd.
Date: 05-2014
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMM.553.327
Abstract: Besides the prevention strategies against early stage dental caries, restoration is a preferable way to prevent decayed tooth from further deterioration. This study aimed to compare the mechanical strengths of carious tooth, traditionally restored tooth, and novel conservatively restored teeth under occlusal loading. The two-dimensional (2D) finite element method (FEM) was applied to quantify and compare maximum tensile stresses thereby predicting the initiation of crack. Taking into consideration of peak tensile stresses, it was found that the conservative (minimal intervention) restorations exhibited better fracture resistance than traditional restoration.
Publisher: Elsevier BV
Date: 12-2019
Publisher: Trans Tech Publications, Ltd.
Date: 05-2014
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMM.553.322
Abstract: This study aims to analyze the functional contact pressure induced by Removable Partial Denture (RPD) by using a 3D finite element (FE) model constructed based on patient specific CT scans. This model was validated against the in vivo test results. The outcomes demonstrate that the finite element simulation has the capability of quantifying localized stress distribution in a complicated denture-mucosa contact problem, with a reasonable matching to clinical measurements of occlusal force and pressure distribution. The methodology is of considerable clinical implication to improve the long term outcomes of the denture treatment.
Publisher: Wiley
Date: 02-2001
DOI: 10.1046/J.1365-2842.2001.00642.X
Abstract: This study aimed to determine Young's modulus, shear modulus and Poisson's ratio of some metal alloys and dental porcelains used in fixed prosthodontics using the technique of impulse excitation of vibration. It also aimed to compare Young's modulus values of these materials with those obtained using the other two methods: the four-point flexural test and the indentation test using the ultra micro-indentation system (UMIS). Five types of metal alloys and four types of dental porcelains were tested. The s les were prepared to a rectangular shape of approximately 8 x 30 x 1.5 mm. Frequency of vibration in a s le was read when a singular elastic strike was made with an impulse tool. The elastic constants were calculated from the frequency of vibration, dimension and mass of each s le. Young's modulus values resulting from the impulse excitation of vibration are not significantly different (P<0.05) from those obtained using the flexural test and the UMIS test in most metal alloys but are different in titanium, titanium alloy and most of the dental porcelains. The technique of impulse excitation of vibration has proven to be an accurate method and is simple to operate. The elastic properties of these alloys and porcelains are essential for determining the other mechanical properties (fracture toughness) and are relevant in clinical application.
Publisher: Elsevier BV
Date: 05-1980
Publisher: Wiley
Date: 03-10-2016
DOI: 10.1111/JOOR.12356
Abstract: 18F-fluoride positron emission tomography (PET) can identify subtle functional variation prior to the major structural change detectable by X-ray. This study aims to investigate the mechanobiological bone reaction around the abutment tooth and in the residual ridge, induced by insertion of removable partial denture (RPD) within two different groups of patients: patients without denture experience (Group 1) and patients with denture experience before (Group 2), using 18F-fluoride PET imaging technique. 18F-fluoride PET/computerised tomography (CT) scan was performed to examine the bone metabolic change in mandible before and after the RPD treatment. Region of interests (ROIs) were placed in alveolar bone around abutment tooth and in residual bone beneath the RPD. Standardised uptake value (SUV), reflecting the accumulation of 18F-fluoride, was measured for each ROI. In all subjects of Group 1, SUVs after insertion were higher than before in both alveolar bone and residual bone, while there was less significant change in SUV in subjects of Group 2. This study demonstrated using longitudinal 18F-fluoride PET scans to effectively examine the bone metabolic change in mandible induced by occlusal loading after RPD insertion. Using this technique, within the six subjects in this study, it was shown that bone metabolism around abutment tooth and residual ridge increased after RPD insertion in case of first-time denture user, while there was no big change in the patient with experience of denture before. This study revealed the effectiveness of applying PET to evaluate bone metabolic activity as mechanobiological reaction.
Publisher: Informa UK Limited
Date: 07-2002
Publisher: Elsevier BV
Date: 1989
Publisher: Springer Science and Business Media LLC
Date: 22-12-2015
Publisher: Elsevier BV
Date: 05-1998
Publisher: Springer Science and Business Media LLC
Date: 10-1989
DOI: 10.1007/BF01730053
Publisher: Informa UK Limited
Date: 1997
Publisher: Elsevier BV
Date: 05-2004
Publisher: Elsevier BV
Date: 10-2006
DOI: 10.1016/J.PROSDENT.2006.07.005
Abstract: The purpose of this literature review was to identify the etiological factors of failure of soldered bars in bar attachment systems for removable implant overdentures. A search of MEDLINE using the key words "bar attachment systems" was performed of English language peer-reviewed journals published between 1975 and 2005. Clinical studies of implant overdentures with prosthodontic maintenance complications of bar attachment systems were identified to establish the perceived etiology of failure. A further search of MEDLINE using the key words "solder joint" was also performed of the fixed prosthodontic literature to identify specific factors affecting the strength, fatigue resistance, and quality of gold solder joints used for bar attachment systems. The first search on bar attachment systems produced evidence of low failure rates of interabutment bars, but higher failure rates of bars where distal cantilever extensions were used. There were no explanations or descriptions of the nature of those failures in the clinical studies reviewed. The second search on fixed prosthodontic literature identified multiple factors that could potentially relate to the failed solder joints with bar attachments. Two potential sites of failure in bar attachments with distal cantilevers were identified, and a simple estimate of the tensile stresses at the solder joints was performed. The values found are comparable to the fatigue failure stresses reported in the searched literature.
Publisher: Wiley
Date: 30-05-2006
Publisher: Elsevier BV
Date: 12-2016
DOI: 10.1016/J.DENTAL.2016.06.007
Abstract: The aim of this in vitro study was to evaluate the effect of core ceramic grinding on the fracture behaviour of bilayered zirconia under two loading schemes. Interfacial surfaces of sandblasted zirconia disks (A) were ground with 80 (B), 120 (C) and 220 (D) grit diamond discs, respectively. Surface roughness and topographic analysis were performed using a confocal scanning laser microscope (CSLM) and a scanning electron microscopy (SEM). Relative monoclinic content was evaluated using X-ray diffraction analysis (XRD) then reevaluated after simulated veneer firing. Biaxial fracture strength (σ) and Weibull modulus (m) were calculated either with core in compression (subgroup Ac-Dc) or in tension (subgroup At-Dt). Facture surfaces were examined by SEM and energy dispersive X-ray spectroscopy (EDS). Maximum tensile stress at fracture was estimated by finite element analysis. Statistical data analysis was performed using Kruskal-Wallis and one-way ANOVA at a significance level of 0.05. As grit size of the diamond disc increased, zirconia surface roughness decreased (p<0.001). Thermal veneering treatment reversed the transformation of monoclinic phase observed after initial grinding. No difference in initial (p=0.519 for subgroups Ac-Dc) and final fracture strength (p=0.699 for subgroups Ac-Dc p=0.328 for subgroups At-Dt) was found among the four groups for both loading schemes. While coarse grinding slightly increased final fracture strength reliability (m) for subgroups Ac-Dc. Two different modes of fracture were observed according to which material was on the bottom surface. Components of the liner porcelain remained on the zirconia surface after fracture for all groups. Technician grinding changed surface topography of zirconia ceramic material, but was not detrimental to the bilayered system strength after veneer application. Coarse grinding slightly improved the fracture strength reliability of the bilayered system tested with core in compression. It is recommended that veneering porcelain be applied directly after routine lab grinding of zirconia ceramic, and its application on rough zirconia cores may be preferred to enhance bond strength.
Publisher: Elsevier BV
Date: 2019
DOI: 10.1016/J.MSEC.2018.08.056
Abstract: To elucidate the bioactivity and bone regeneration of porous titanium surfaces treated using acid-alkali combination, and to define the optimal alkali reaction time. Ten groups of porous Ti with at least 3 per group undergoing different acid-alkali treated time were prepared. The surface was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), bicinchoninic acid method (BCA), optical contact angle measurement and Raman spectrometry. Compression testing was performed with a universal testing machine. The bioactivity and osteoinduction were evaluated by a series of biological tests using a simulated body fluid (SBF) test, cell proliferation test, vinculin, ALP and OCN expression, and cell mineralization. The acid-alkali treatment formed micro- and nano-scale structures on the s le surfaces. The alkali treatment for 12 h achieved the sharpest nano-scale surface relief and the most protein absorption. The treated porous surface was coated with a NaHTiO Acid-alkali treatment is an effective means of generating nano-scale relief on porous Ti surface, and is beneficial for bioactivity and bone regeneration. The 15 min acid and 12 h alkali etching is the optimal combination. The osteoinductive efficacy may be attributable to the surface physical chemistry and the formation of hydroxyapatite and perovskite layers, rather than direct cell adhesion and proliferation.
Publisher: Elsevier BV
Date: 03-2014
DOI: 10.1016/J.BIOMATERIALS.2013.12.088
Abstract: As information on osteoblast mechanosensitivity response to biomechanical cues in three-dimensional (3D) in vitro microenvironments is sparse, the present study compared morphogenesis of primary human alveolar bone osteoblasts (PHABO) under microchip-based 3D-static conditions, and 3D-fluid flow-mediated biomechanical stimulation in perfusion bioreactors. Discrimination of the respective microenvironment by differential morphogenesis was evident from fluid flow-induced PHABO reorganization into rotund bony microtissue, comprising more densely packed multicellular 3D-aggregates, while viability of microtissues was flow rate dependent. Time-lapse microscopy and simple modeling of biomechanical conditions revealed that physiologically relevant fluid flow-mediated PHABO stimulation was associated with formation of mulberry-like PHABO aggregates within the first 24 h. Differential extracellular matrix deposition patterns and gene expression modulation in PHABO aggregates at day 7 further indicates progressive osteoblast differentiation exclusively in perfusion culture-developed bony microtissues. The results of our study strongly suggest PHABO morphogenesis as discriminator of microenvironmental growth conditions, which in case of the microfluidic 3D microchip-bioreactor are substantiated by triggering in vitro bone microtissue formation concomitant with progressive osteoblastic differentiation. Such microtissue outcomes provide unique insight for mechanobiological studies in response to biomechanical fluid flow cues, and clinically appear promising for in vitro PHABO preconditioning, enabling innovative bone augmentation procedures.
Publisher: Wiley
Date: 1992
Publisher: Elsevier BV
Date: 07-2009
DOI: 10.1016/J.DENTAL.2009.01.006
Abstract: The metastability of the tetragonal phase of yttria tetragonal zirconia polycrystalline (Y-TZP) ceramics is a cause for concern in dental crown and bridge applications. One specific problematic area is the nature of the interface between the veneering porcelain and the Y-TZP framework and whether the associated preparation procedures and reactions result in a reduction of the stability of the zirconia. To investigate this aspect, high-resolution SEM observations were made of polished and etched (HF content gel) cross-sections of the interface area. Dry and moist veneering porcelain powders were built up on the zirconia base. In some instances the zirconia grains at the interface appear to show multiplicity of subgrain faceting whereas in other instances they do not. The latter indicate destabilisation of the tetragonal phase occurs and in addition that the porcelain veneering material wets and some dissolution of the Y-TZP occurs. These results and their relevance to the long-term stability of the interface adhesion to the veneering porcelain as well as possible tetragonal to monoclinic crystal transformations at the interface are discussed.
Publisher: Elsevier BV
Date: 08-2009
DOI: 10.1016/J.JMBBM.2008.09.002
Abstract: Load response of viscoelastic-plastic materials depends on the load magnitude and history, and can be described by rheological models consisting of springs and dashpots. The parameters in these models can be obtained by instrumented indentation. Time-dependent properties are determined best from the time course of indenter displacement under constant load, but one must consider also the initial loading history. For characterization of instantaneous elastic and plastic response, fast loading and unloading are necessary. The paper summarizes the formulae for indentation into elastic-plastic and viscoelastic-plastic materials, and proposes a procedure for testing and data evaluation. Its application is illustrated on the indentation of human enamel.
Publisher: Springer Science and Business Media LLC
Date: 1991
DOI: 10.1007/BF00769951
Publisher: Elsevier BV
Date: 12-2008
DOI: 10.1016/J.ARCHORALBIO.2008.06.013
Abstract: The quantification of biomechanical response of mandibular bone to mastication is an integral component for a key in understanding the biological consequence of masticatory functions. Understanding the response of mandibular bone to external loading may also well explain the mechanisms of bone turnover. In this study, three finite element (FE) models simulating the lower second premolar, first and second molars along with their supporting structures were developed to determine stress/strain levels and distribution under different occlusal loading. The changes in stress/strain values and profiles have been investigated in three scenarios: pre-extraction of the lower first molar, post-extraction and after full healing of the extracted socket. The mastication induced equivalent strains within the supporting mandibular bone at each of these three scenarios were quantified and compared against the Frost's mechanostat theory. The results of stress/strain profiles show considerably lower magnitudes in the post-extracted and healed scenarios compared with the pre-extraction case. Following the Frost's MES hypothesis, the initial equivalent strains are related to local bone remodelling. It is found that in the extracted case the bone near the tooth socket undergoes resorption from lingual respect whilst filling the cavity, whereas in the healed case bone turnover reaches equilibrium. The results provide important data for clinical assessment of constructing dentures or other restorative devices.
Publisher: Wiley
Date: 06-10-2010
DOI: 10.1111/J.1600-0501.2010.02019.X
Abstract: To introduce a new strain gauge approach to assess the fit of fixed implant frameworks. A partially edentulous epoxy resin mandible model received two Straumann implants in the area of the lower left second premolar and second molar. The model was used to fabricate four zirconia and four identical cobalt-chromium alloy frameworks using a laboratory computer-aided design/computer-aided manufacturing (CAD/CAM) system. A total of four linear strain gauges were then bonded around each implant on the peri-implant structure (mesial, distal, buccal, and lingual). The experimental part was composed of two phases: qualitative and quantitative. For the qualitative assessment, the model was verified by recording the response of each strain gauge while applying a near-constant force of known directions on each implant. For the quantitative phase, the frameworks were attached on the implants and the screws were torqued to 15 N cm. In the qualitative phase, the strain gauge response to every force direction was recorded. After attaching the frameworks, all frameworks produced measurable strains, but with different strain patterns. Upon correlating the two phases, the zirconia frameworks were found to be slightly smaller than the inter-implant distance, whereas the cobalt-chromium alloy frameworks tended to be slightly larger than the inter-implant distance. The proposed technique is not only valid for detecting implant framework misfit but also for determining the form of inaccuracies. Model verification is an essential informative step to aid the interpretation of the pattern of framework distortion.
Publisher: Springer Science and Business Media LLC
Date: 1978
DOI: 10.1007/BF00739290
Publisher: No publisher found
Date: 2002
Publisher: SAGE Publications
Date: 03-2008
DOI: 10.1177/154405910808700315
Abstract: Reconstitution of carious dentin has been recognized as difficult, because it progresses by loss of collagen polymerization and by demineralization under acidic conditions. Recently, colloidal alkaline nano-calcium phosphate, prepared by electrical discharge in a buffered physiological saline solution, has been shown to be effective in the formulation of a bone-like biocomposite by simply being mixed with acidic collagen solution. It was hypothesized that colloidal calcium phosphate was suitable for the reconstitution of carious dentin. Natural caries lesions in dentin from permanent teeth were exposed to colloidal hydroxyapatite and β-tricalcium phosphate for 10 days. The micromechanical properties of these tissues were evaluated by nano-indentation. The elastic modulus of human carious dentin improved after s les were immersed in colloidal β-tricalcium phosphate. The mineral density of carious dentin exposed to β-tricalcium phosphate increased more than that immersed in hydroxyapatite. However, since it was not directly proportional to micromechanical recovery, mineral density alone was not a sufficient indicator of mechanical behavior.
Publisher: Elsevier BV
Date: 04-1976
Publisher: Elsevier BV
Date: 08-2006
DOI: 10.1016/J.JDENT.2005.11.004
Abstract: The aim of this study was to measure the influence of water on the adhesion between titanium and porcelain by means of the strain energy release rate (G-value or interfacial toughness). Rectangular specimens of grade II titanium and a reference gold-palladium porcelain fused to metal (PFM) alloy were veneered with feldspathic porcelains. In the case of the titanium, two gold and one ceramic bonder systems were used to enhance the adhesion of the porcelain. The G-value was measured with a four-point bending configuration developed by Charalambides et al. (Journal of Applied Mechanics (Trans ASME). 1989 :77-82), at four different loading rates (from 0.1 to 15 N/s) in water and at one loading rate (1.5 N/s) in kerosine. There was a significant difference (ANOVA, p<0.01) in the interfacial toughness between the different bonding systems, with the two goldbonder systems exhibiting higher toughness in kerosine and water than the ceramic bonder. The two goldbonders achieved the best results across all loading rates. Their interfacial toughness, tested in kerosine, varied between 45.83+/-6.72 and 73.54+/-17.01 J/m(2) and tested in water from 40.86+/-2.23 to 69.17+/-12.33 J/m(2), respectively. The ceramic Ti bonder achieved the lowest G-values throughout (30.15+/-5.52 J/m(2) in kerosine to 11.08+/-2.18 J/m(2) in water). The gold-palladium PFM alloy showed more constant behaviour (33.48+/-2.24 J/m(2) to 23.07+/-0.53 J/m(2) in kerosine and water, respectively). Compared to the gold-palladium PFM alloy, the goldbonders achieved much higher G-values whereas the ceramic Ti bonder G-values were lower when tested in water and in kerosine.
Publisher: Elsevier BV
Date: 08-2019
Publisher: Wiley
Date: 22-02-2011
DOI: 10.1111/J.1600-0722.2011.00810.X
Abstract: Despite the advantages of glass-ionomer cement (GIC) restorative materials, they exhibit low mechanical properties and are susceptible to dissolution. The purpose of this study was to investigate the existence of self-reparability of a GIC material. Thirty Fuji IX discs were fabricated and subjected to desiccation. The discs were randomly separated into three groups: one group was kept in air, a second group was soaked in water, and a third group was placed in casein phosphoprotein-amorphous calcium phosphate-containing solution (Dentacal NSI, Hornsby, Australia). After 21 d of incubation, all specimens were subjected to biaxial flexure testing. One-way ANOVA revealed a statistical difference in the biaxial flexure strength between the groups. Weibull statistics revealed that the Dentacal group demonstrated a lower probability of failure than the other groups. The air group exhibited the highest probability of failure. The difference between the specimens was expected as a result of enhanced cross-linking between the polyalkenoate chains and the GIC particles, and the diffusion of ionic components to the set GIC. Therefore, perhaps a form of reparative mechanism exists for precrazed GIC when it is exposed to a remineralizing solution. In addition to the benefit on natural tooth structures, this study indicates that remineralizing solutions are also beneficial for maintaining the mechanical integrity of GIC restorations.
Publisher: Elsevier BV
Date: 1994
Publisher: Springer Science and Business Media LLC
Date: 06-06-2013
DOI: 10.1007/S00414-013-0874-Z
Abstract: To assess the usefulness of scanning electron microscopy and energy dispersive x-ray spectroscopy in matching bullet wipe to the bullet. Bullet wipe can be used to match a bullet type to a crime scene.
Publisher: Japan Prosthodontic Society
Date: 10-2017
DOI: 10.1016/J.JPOR.2016.12.010
Abstract: This study combines clinical investigation with finite element (FE) analysis to explore the effects of buccal bone thickness (BBT) on the morphological changes of buccal bone induced by the loaded implant. One specific patient who had undergone an implant treatment in the anterior maxilla and experienced the buccal bone resorption on the implant was studied. Morphological changes of the bone were measured through a series of cone-beam computed tomography (CT) scans. A three-dimensional heterogeneous nonlinear FE model was constructed based on the CT images of this patient, and the in-vivo BBT changes are correlated to the FE in-silico mechanobiological stimuli namely, von Mises equivalent stress, equivalent strain, and strain energy density. The anterior incisory bone region of this model was then varied systematically to simulate five different BBTs (0.5, 1.0, 1.5, 2.0, and 2.5mm), and the optimal BBT was inversely determined to minimize the risk of resorption. Significant changes in BBTs were observed clinically after 6 month loading on the implant. The pattern of bone resorption fell into a strong correlation with the distribution of mechanobiological stimuli onsite. The initial BBT appeared to play a critical role in distributing mechanobiological stimuli, thereby determining subsequent variation in BBT. A minimum initial thickness of 1.5mm might be suggested to reduce bone resorption. This study revealed that the initial BBT can significantly affect mechanobiological responses, which consequentially determines the bone remodeling process. A sufficient initial BBT is considered essential to assure a long-term stability of implant treatment.
Publisher: Wiley
Date: 25-07-2018
DOI: 10.1111/ADJ.12624
Abstract: The aim of this study was to develop and evaluate a method for synthesizing a stable suspension of hydroxyapatite nanoparticles and to test its efficacy for remineralizing carious enamel lesions. Hydroxyapatite (HA) particles were synthesized using wet chemistry. Synthesized particles were introduced into a high-pressure homogenizer (5-10 homogenization passes at 15 000 psi) in the presence of different stabilizers. Size and distribution of the resultant particles were determined using dynamic light scattering (DLS). The morphology and composition of the nanoparticles were determined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Subsequently, artificial lesions were treated with HA nanosuspension plus artificial saliva or a fluoride-containing artificial saliva only. Visual analysis and quantification of the lesion mineral density before and after remineralization were performed using microcomputed tomography. DLS and SEM results confirmed the formation of nonagglomerated HA nanoparticles (20-40 nm) following high-pressure homogenization treatment. Quantitative evaluation of the lesions showed that remineralization of the lesion with hydroxyapatite nanosuspension led to a significantly higher level of mineral gain compared to the control group (P < 0.05). High-pressure homogenization is an effective method for facile preparation of a stable suspension of hydroxyapatite nanoparticles. Treatment of artificial lesions with nonagglomerated spherical HA nanoparticles improves the remineralization of enamel lesion.
Publisher: Elsevier BV
Date: 07-2010
DOI: 10.1016/J.JDENT.2010.04.012
Abstract: The aim of the study was to compare the relative amounts and nature of the proteinous content of sound and molar-incisor hypomineralisation (MIH) enamel. TCA (20%) was used to dissolve the mineral phase and precipitate the proteins from enamel pieces sectioned from sound and MIH enamel. The protein content was estimated using a miniaturized version of the method of Lowry et al. S les of the solubilised protein were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), stained with Coomassie Blue R250 and tryptic fingerprint/mass spectrometry (MS/MS) of bands in excised gel pieces used for protein identification. Compared to sound enamel, brown enamel showed a 15-21-fold higher protein content, and yellow and chalky enamel showed about 8-fold higher protein content. Tryptic fingerprint/MS performed on excised 50-70kDa areas demonstrated serum albumin, type I collagen and antitrypsin to be common to all types of enamel. Yellow and brown enamel showed more abundant serum albumin and antitrypsin, and the presence of serum antithrombin. Albumin is reported to be an inhibitor of crystal growth, and antitrypsin and antithrombin inhibit kallikrein 4 proteolytic activity. The combination of the effects of serum proteins on developing enamel may result in elevated proteinous content and reduced mineral content as seen in MIH enamel.
Publisher: Wiley
Date: 11-2011
Publisher: The Royal Society
Date: 05-2018
DOI: 10.1098/RSOS.171699
Abstract: Mammalian tooth wear research reveals contrasting patterns seemingly linked to diet: irregularly pitted enamel surfaces, possibly from consuming hard seeds, versus roughly aligned linearly grooved surfaces, associated with eating tough leaves. These patterns are important for assigning diet to fossils, including hominins. However, experiments establishing conditions necessary for such damage challenge this paradigm. Lucas et al . (Lucas et al . 2013 J. R. Soc. Interface 10 , 20120923. ( doi:10.1098/rsif.2012.0923 )) slid natural objects against enamel, concluding anything less hard than enamel would rub, not abrade, its surface (producing no immediate wear). This category includes all organic plant matter. Particles harder than enamel, with sufficiently angular surfaces, could abrade it immediately, prerequisites that silica/silicate particles alone possess. Xia et al. (Xia, Zheng, Huang, Tian, Chen, Zhou, Ungar, Qian. 2015 Proc. Natl Acad. Sci. USA 112 , 10 669–10 672. ( doi:10.1073 nas.1509491112 )) countered with experiments using brass and aluminium balls. Their bulk hardness was lower than enamel, but the latter was abraded. We examined the ball exteriors to address this discrepancy. The aluminium was surfaced by a thin rough oxide layer harder than enamel. Brass surfaces were smoother, but work hardening during manufacture gave them comparable or higher hardness than enamel. We conclude that Xia et al .'s results are actually predicted by the mechanical model of Lucas et al . To explain wear patterns, we present a new model of textural formation, based on particle properties and presence/absence of silica(tes).
Publisher: Elsevier BV
Date: 08-2009
DOI: 10.1016/J.JDENT.2009.03.019
Abstract: The aim of this study is to illustrate the graded proper properties of enamel from the outer (near occlusal surface) to the inner region (near enamel-dentine junction) in a cross-sectioned surface and discuss how natural design achieve the graded functions. Nanoindentation, Raman spectroscopes, and SEM were employed to compare the inner and outer regions of the cross-sectioned enamel from different angles, namely mechanical properties such as elastic modulus and hardness, indentation energy absorption ability, indentation creep ability, indentation residual stress distribution pattern, compositional differences, and microstructural differences. Inner enamel has lower elastic modulus and hardness but higher creep and stress redistribution abilities than outer counterpart, which is related to the gradual compositional change through the enamel. Enamel can be regarded as a functionally graded natural biocomposite, which will require special attention using numerical analysis to fully appreciate the consequences of such a structure for the mechanical behaviour of teeth and restorations placed therein. Moreover, the smart design of nature can be a good model for us in functional graded materials/coatings design and development.
Publisher: Springer Science and Business Media LLC
Date: 06-1980
DOI: 10.1007/BF00752140
Publisher: Wiley
Date: 11-02-2005
DOI: 10.1111/J.1365-2842.2004.01408.X
Abstract: The present study examines the influence of a goldbonder and pre-heat treatment of the titanium on the adhesion of porcelain. Three groups of titanium substrates were given various heat treatments, namely none, 200 degrees and 600 degrees C, respectively before applying goldbonder. The surfaces of the titanium specimens following heat treatment were examined with an electron spectroscopy for chemical analysis (ESCA). The adhesion strength was measured by the strain energy release rate (G), which was proposed by Suansuwan N and Swain MV (Int J Prosthodont. 1999 :547). After bonding porcelain onto titanium substrates with the aid of the goldbonder, the porcelain side of specimens was notched to the interface with a thin diamond saw. Then the s les were subject to a four-point bending test. Following fracture testing, specimens were examined with a scanning electron microscope (SEM) and SEM with energy-dispersive spectroscopic analysis (EDS). The mean G-values were 38.87, 28.64 and 16.33 J m(-2), respectively. ESCA analysis showed the composition of aluminium of the surface of 600 degrees C pre-heat treatment became richer than that of the others. SEM images of the fracture surfaces showed that for the 600 degrees C pre-heat treatment fracture occurred within the oxidation layer on the titanium. High temperature pre-heat treatment prior to bonding significantly reduces porcelain bonded to titanium with the goldbonder. The Influence of Goldbonder and Pre-heat Treatment on the Adhesion of Titanium Alloy and Porcelain.
Publisher: Wiley
Date: 1982
Publisher: Elsevier BV
Date: 2003
Abstract: The relationship between the topographical variations in the structural, biochemical and dynamic biomechanical properties of articular cartilage (AC) before and 6 months after meniscectomy has not been previously reported but is clearly relevant to our understanding of the role of mechanical factors on the pathogenesis of osteoarthritis (OA). The objective of this study was to address this deficiency using an ovine model of OA induced by bilateral lateral meniscectomy. The dynamic effective shear modulus (G*) and phase lag were determined ex vivo at 26 in idual locations over the medial and lateral tibial plateaux of non-operated and meniscectomized ovine joints 6 months after surgery using a novel hand-held dynamic indentation probe. AC thickness was measured with a needle penetration probe. The AC from the same topographical locations as indented was then analysed for sulfated glycosaminoglycans (S-GAG) as a measure of proteoglycan (PG) levels, collagen and water content. Histological evaluation of the collagen organization using quantitative analysis of birefringence intensity was performed on stained tissue sections from the same topographical locations of each animal. It was demonstrated that the AC of the entire lateral tibial compartment of the meniscectomized joints underwent significant local degenerative and compensatory changes as indicated by a decreased G* and an increase in phase lag and water content. This was accompanied by a decrease in PG content of the AC of the middle and inner regions. While the AC of the outer region of the lateral meniscectomized compartment showed a marked increase in PG content and a more than two-fold increase in thickness, these tissues were also found to be structurally inferior, as indicated by a decreased G* and abnormal collagen birefringence intensity. The AC thickness was elevated at all locations of the lateral and medial tibial plateau of the meniscectomized joints. Strong and significant correlations between the biomechanical and biochemical data were established for a number of the parameters examined, especially between collagen content and G*, collagen content and AC thickness, and G* and AC thickness. An inverse correlation between S-GAG content and G* was only apparent in non-operated control tissues, whereas correlations between collagen and water content, water content and G*, and water content and thickness were evident for AC of the meniscectomized tibial plateaux. Less striking changes were noted in the medial compartment where the intact meniscus remained in place. However, elevated PG content, thicker AC together with slight changes in G* suggested an early hypertrophic response in these tissues. This study has highlighted the variable response of AC in different topographical regions of meniscectomized joints to the altered mechanical stresses introduced by this surgical procedure. The AC at the joint margins, while thicker and richer in PG, was found to be biomechanically softer (lower shear modulus) than normal AC, and because of this, would be expected to undergo degenerative changes with time leading to the onset of OA.
Publisher: Elsevier BV
Date: 12-2014
DOI: 10.1016/J.PROSDENT.2014.08.002
Abstract: The wear behavior of human enamel that opposes different prosthetic materials is still not clear. The purpose of this in vitro study was to investigate and compare the friction and wear behavior of human tooth enamel that opposes 2 indirect restorative materials: lithium disilicate glass ceramic and Type III gold. Friction-wear tests on human enamel (n=5) that opposes lithium disilicate glass ceramic (n=5) and Type III gold (n=5) were conducted in a ball-on-flat configuration with a reciprocating wear testing apparatus. The wear pairs were subjected to a normal load of 9.8 N, a reciprocating litude of approximately 200 μm, and a reciprocating frequency of approximately 1.6 Hz for up to 1100 cycles per test under distilled water lubrication. The frictional force of each cycle was recorded, and the corresponding friction coefficient for different wear pairs was calculated. After wear testing, the wear scars on the enamel specimens were examined under a scanning electron microscope. Type III gold had a significantly lower steady-state friction coefficient (P=.009) and caused less wear damage on enamel than lithium disilicate glass ceramic. Enamel that opposed lithium disilicate glass ceramic exhibited cracks, plow furrows, and surface loss, which indicated abrasive wear as the prominent wear mechanism. In comparison, the enamel wear scar that opposed Type III gold had small patches of gold smear adhered to the surface, which indicated a predominantly adhesive wear mechanism. A lower friction coefficient and better wear resistance were observed when human enamel was opposed by Type III gold than by lithium disilicate glass ceramic in vitro.
Publisher: No publisher found
Date: 1994
Publisher: Elsevier BV
Date: 11-2003
Publisher: Elsevier BV
Date: 2008
DOI: 10.1016/J.ACTBIO.2007.06.011
Abstract: Adhesive resin-based restorative materials have the potential to considerably strengthen teeth and offer more economically viable alternatives to traditional materials such as gold, amalgam or ceramics. Other advantages are direct and immediate placement and the elimination of the use of mercury. However, polymerization shrinkage during curing of an adhesive restoration and mismatch in mechanical properties can lead to the initiation and development of interfacial defects. These defects could have a detrimental effect on the longevity of the restored tooth. The current study is focused on some design issues of resin-based composites affecting the longevity of the tooth-restoration interface. The theoretical approach is based on self-consistent micromechanical modelling that takes into account the effect of the material properties, volume concentration of the dispersed particle phase as well as the shape of these particles on the overall thermomechanical properties of the composite. Results obtained for resin-based composites reinforced with spherical, disc and short fibre particles highlight the advantages of disc shaped and short fibre particles.
Publisher: Elsevier BV
Date: 09-2010
DOI: 10.1016/J.BIOMATERIALS.2010.05.077
Abstract: This paper aims to establish a relationship between the surface morphology induced micromechanics and bone remodeling responses to a solid bead coated porous implant and further to develop a multiobjective optimization framework for the coating design of biomaterials. Multiscale modeling and remodeling techniques were developed, where a macroscopic analysis was initially performed to generate a global response to enable a microscopic analysis. The bone remodeling responses of the microscopic models (with a specific surface morphology) were evaluated in terms of the average apparent density developed in the peri-implant region. To explore the proposed multiscale analysis and design methods, a typical dental implantation setting is exemplified in this study. The response surface method (RSM) was utilized to relate the major implant coating parameters to the bone responses. It is found that increasing the volume fraction of the coating beads articles results in a greater bone density, whereas increasing bead article size does not significantly affect the bone's responses. Several different multiobjective optimization schemes were adopted to optimize the coated bead size and volume fraction, which reveal that the optimal design parameters of particle diameter and volume fraction are 100 microm--35% and 38 microm--17.5% for the cortical and cancellous bones respectively, agreeing with clinical data. To maximize the implant/bone interfacial stability, specific surface coating designs for particular locations are recommended.
Publisher: S. Karger AG
Date: 2009
DOI: 10.1159/000226230
Abstract: Desktop microcomputed tomography (micro-CT) offers a non-invasive 3-dimensional analysis of structures and their physical properties. To date, the use of micro-CT has mostly involved qualitative observations, with the extent of quantitative analysis relying on automated internal calibration by the micro-CT control software. However, the value of such calibration is limited by machine drift. For an accurate quantitative use of micro-CT, it is recognized that external means of calibration are needed. A novel system of calibration standards, also known as ‘phantoms’, is presented. A range of low mineral concentration phantoms involving triethylene glycol dimethacrylate/glycerolate dimethacrylate resin mixed with commercial pure hydroxyapatite (HAP), from 0.07 to 1.05 g/cm sup /sup , was fabricated. Sintered HAP was impregnated with the same resin, producing phantoms with medium-level mineral concentrations up to 1.90 g/cm sup /sup . These phantoms were easy to create, proved accurate and stable with repeated use, and were found to mimic the composite nature of dental enamel and dentine structures under investigation.
Publisher: Elsevier BV
Date: 02-2015
DOI: 10.1016/J.DENTAL.2014.10.008
Abstract: To examine the effect of ultraviolet light (UV) treatment on the surface characteristics of two acid-etched zirconia-based dental implant materials. Discs of two zirconia-based materials (Zr1 and Zr2) with smooth (m) and roughened (r) surfaces were treated by UV light for 15min. The surface topography was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface elemental composition of all s les was determined by X-ray photoelectron spectroscopy (XPS), the crystalline property by X-ray diffraction (XRD) and the hydrophilic status by contact angle (CA) measurements of a water droplet. SEM and AFM revealed quantitative and qualitative differences between the roughened and smooth surfaces. UV treatment did not induce any topographic changes of the tested surfaces (p>0.05). All UV-treated s les showed a significant surface elemental content change with a decrease of carbon by 43-81%, an increase of oxygen by 19-45%, and an increase of zirconia by 9-41%. Upon UV treatment, a 19-25% increase of the crystalline monoclinic phase was observed on surfaces of material Zr1, whereas a slight increase on the smooth Zr2 surface (+3%) and a decrease on the roughened Zr2 surface by 20% was observed. For all s les, the hydrophilic status changed significantly from hydrophobic to hydrophilic by UV treatment (p<0.0001). The average contact angles were between 56.4° and 69° before and 2.5° and 14.1° after UV-light treatment. UV treatment altered the physicochemical properties of the two zirconia implant surfaces investigated. The mechanism by which such changes are induced requires further investigation.
Publisher: No publisher found
Date: 1991
Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.JMBBM.2018.08.034
Abstract: This study aimed to develop a simple and efficient numerical modeling approach for characterizing strain and total strain energy in bone scaffolds implanted in patient-specific anatomical sites. A simplified homogenization technique was developed to substitute a detailed scaffold model with the same size and equivalent orthotropic material properties. The effectiveness of the proposed modeling approach was compared with two other common homogenization methods based on periodic boundary conditions and the Hills-energy theorem. Moreover, experimental digital image correlation (DIC) measurements of full-field surface strain were conducted to validate the numerical results. The newly proposed simplified homogenization approach allowed for fairly accurate prediction of strain and total strain energy in tissue scaffolds implanted in a large femur mid-shaft bone defect subjected to a simulated in-vivo loading condition. The maximum discrepancy between the total strain energy obtained from the simplified homogenization approach and the one obtained from detailed porous scaffolds was 8.8%. Moreover, the proposed modeling technique could significantly reduce the computational cost (by about 300 times) required for simulating an in-vivo bone scaffolding scenario as the required degrees of freedom (DoF) was reduced from about 26 million for a detailed porous scaffold to only 90,000 for the homogenized solid counterpart in the analysis. The simplified homogenization approach has been validated by correlation with the experimental DIC measurements. It is fairly efficient and comparable with some other common homogenization techniques in terms of accuracy. The proposed method is implicating to different clinical applications, such as the optimal selection of patient-specific fixation plates and screw system.
Publisher: Springer Science and Business Media LLC
Date: 07-1997
Abstract: Ion implantation of polyethylene terephthalate (PET) and polystyrene (PS) with various high energy metallic ions at 70 kV and a dose of 3 × 10 16 ions/cm 2 has been made. Measurements of the mechanical properties of the polymers before and after implantation have been made with an ultra microindentation system using both pointed and a small (2 μm) radius spherical-tipped indenter. The surface regions were also investigated by atomic force microscopy (AFM) and Rutherford backscattering (RBS). Significant differences have been observed between the Ti–B dual-implanted surfaces and those of the Au and W implanted surfaces. For both the PET and PS, the resistance to indenter penetration at very low loads was much greater for the Ti–B dual-implanted surfaces. The estimated maximum hardness and modulus of the implanted materials were 0.3 and 8 GPa for the PET material and 1.4 and 16 GPa for the PS material. The results obtained with the spherical indenter show a gradual decline in effective modulus of the surface with penetration depth, whereas the hardness or contact pressure goes through a maximum before declining asymptotically to the bulk values. The values of hardness estimated for the spherical-tipped indenter are somewhat more conservative than the optimistic estimates with the Berkovich indenter. The improved increase in hardness for the Ti–B dual-implanted PET material scales with the RBS measured increased depth of implantation.
Publisher: Wiley
Date: 06-1988
Publisher: Elsevier BV
Date: 05-2007
DOI: 10.1016/J.JDENT.2006.12.002
Abstract: The aim of this study is to compare the mechanical responses of enamel with dental-used metals and to show that enamel has mechanical properties similar to metals rather than ceramics. Four dental-used metals: cast alloy, gold alloy, titanium and amalgam, were compared with enamel. Pure hydroxyapatite (HAP) was used as the ceramic analogue of enamel. A Berkovich and a spherical indenter were selected for nanoindentation tests. The stress-strain (H-a/R) curves and indentation creep behaviour were investigated and analyzed. Although the primary composition of enamel is hydroxyapatite, the indentation stress-strain curves and creep behaviour of enamel was totally different to HAP. Enamel had similar stress-strain response to that of cast alloy and gold alloy, all of which showed work-hardening effect. Titanium and amalgam had curves that showed lower stress at comparable strain than enamel and showed no work-hardening. Amalgam exhibited the greatest creep behaviour, followed by Titanium, enamel and gold alloy. Similar to HAP, the cast alloy had very limited creep response. Only enamel showed significant backcreep at minimum load. This may be a consequence of the memory behaviour of the minor protein component within enamel. The small remnant volume fraction of protein fragments have endowed enamel with metallic-like mechanical properties, which impart it with an ability to sustain repetitive cyclic contact loading over the life of the host. It may be better to choose metallic-like dental restorative materials to sustain the severe cyclic contact behaviour experienced and to protect the opposing teeth from excessive damages.
Publisher: Elsevier BV
Date: 2011
DOI: 10.1016/J.ACTBIO.2010.07.040
Abstract: The objective of this study was to calculate stresses produced by polymerization contraction in regions surrounding a dental resin composite restoration. Initial cracks were made with a Vickers indenter at various distances from the edge of a cylindrical hole in a soda-lime glass disk. Indentation crack lengths were measured parallel to tangents to the hole edge. Resin composites (three brands) were placed in the hole and polymerized (two light irradiation protocols) at equal radiation exposures. The crack lengths were re-measured at 2 and 10 min after irradiation. Radial tensile stresses due to polymerization contraction at the location of the cracks (σ(crack)) were calculated from the incremental crack lengths and the fracture toughness K(c) of the glass. Contraction stresses at the composite-glass bonded interface (σ(interface)) were calculated from σ(crack) on the basis of the simple mechanics of an internally pressurized thick-walled cylinder. The greater the distance or the shorter the time following polymerization, the smaller was σ(crack). Distance, material, irradiation protocol and time significantly affected σ(crack). Two-step irradiation resulted in a significant reduction in the magnitude of σ(interface) for all resin composites. The contraction stress in soda-lime glass propagated indentation cracks at various distances from the cavity, enabling calculation of the contraction stresses.
Publisher: Elsevier BV
Date: 03-2013
Publisher: Elsevier BV
Date: 08-2004
Publisher: Springer Science and Business Media LLC
Date: 11-07-2017
Abstract: Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.
Publisher: Elsevier BV
Date: 03-2003
DOI: 10.1016/S0300-5712(03)00025-3
Abstract: This study evaluates the fracture toughness and hardness of three pressable all-ceramic materials: IPS-Empress, Empress 2 and an experimental ceramic material. Fifteen discs and 15 bars per material were prepared. Fracture toughness was measured with two different techniques: indentation fracture and indentation strength. During the indentation fracture tests the hardness of each material was also measured. Statistical significance among groups of population was studied using one-way Anova and Tukey's multiple comparison tests. Fracture toughness results using the indentation strength technique (with three-point bending and biaxial flexure tests) were: IPS-Empress (1.39 (SD 0.3) and 1.32 (SD 0.3)) Empress 2 (3.14 (SD 0.5) and 2.50 (SD 0.3)) MPa x m(1/2) and the experimental ceramic (3.32 (SD 0.6) and 2.43 (SD 0.3)) MPa x m(1/2). The indentation fracture technique generated orthogonal cracks of different lengths for Empress 2 and the experimental ceramic, whether perpendicular or parallel to the lithium disilicate elongated crystals. Thus, two values were reported: Empress 2 (1.5 (SD 0.2) and 1.16 (SD 0.2)) MPa x am(1/2) and the experimental ceramic (1.67 (SD 0.3) and 1.15 (SD 0.15)) MPa x m(1/2). The IPS-Empress indentation fracture result was 1.26 (SD 0.1). The hardness results were: 6.6, 5.3 and 5.5 GPa for IPS-Empress, Empress 2 and the experimental ceramic, respectively. No significant differences in fracture toughness and hardness results were found between Empress 2 and the experimental ceramic (P>0.05 ANOVA). Both materials exhibited fracture toughness anisotropy following pressing. They demonstrated improved fracture toughness and reduced hardness compared with IPS-Empress P<0.05(ANOVA), which should be beneficial for clinical applications.
Publisher: Wiley
Date: 28-02-2012
DOI: 10.1111/J.1834-7819.2011.01638.X
Abstract: In a previous study, the authors used a finite element analysis (FEA) to evaluate the stresses developed during the loading of an all-ceramic, inlay supported fixed partial denture and compared it with the more traditional full crown supported prosthesis. To date there has been little research into correlating the responses of the numerical model against physical mechanical tests such validation analysis is crucial if the results from the FEA are to be confidently relied upon. This study reports on the experimental methods used to compare with the FEA and thereby to validate the predictive fracture behaviour of the numerical model. This study also outlines the methods for manufacture and testing of the ceramic structure along with observations of the fracture tests. In addition the procedure used for developing the FEA model for the test system is outlined.
Publisher: Springer Science and Business Media LLC
Date: 1987
DOI: 10.1007/BF01160553
Publisher: Elsevier BV
Date: 07-2005
DOI: 10.1016/J.JBIOMECH.2004.07.012
Abstract: A better appreciation of the properties of carious dentine would be of clinical advantage in carious assessment and management. The aim of this study is to understand the deterioration of the mechanical properties of carious dentine as a result of bacterial demineralising process as well as change in dentine structures observed under scanning electronic microscope. Eight primary molar teeth with untreated carious dentine were axially sectioned and fine polished for nano-indentation. On each specimen, six lines of indentation, evenly distributed through the lesion, were made from the pulp to lesion cavity floor parallel to tubule direction using nano-indentation (Ultra Micro Indentation System, UMIS-2000), while another two indentation lines were made on an adjacent region of sound dentine in the same manner. All tests were conducted on hydrated specimens. Hardness and elastic modulus decreased significantly and progressively toward the cavity floor varying from 0.56 to 0.001 GPa and 14.55 to 0.015 GPa, respectively. The change in mechanical properties was in a specific pattern as a function of lesion depth, in which the hardness could be fitted to an exponential function, while the variation of the elastic modulus across the entire lesion was fitted to a power law relationship. More critical evaluation of the elastic modulus data indicated that two distinct exponential functions provided an excellent fit to the results. These changes in elastic modulus also matched the structural changes seen across a lesion, which were associated with a change from primarily peritubular to intertubular dissolution.
Publisher: Springer Science and Business Media LLC
Date: 03-2008
Abstract: An amorphous polymer was contacted by a Berkovich indenter using the same loading history but with four different unloading rates following a wide range of load-hold time periods. The strain-rate sensitivity index of the creeping solid was determined at each load-hold period based on two readily determinable parameters, which are the effective contact stiffness and strain rate at the onset of unloading. The measured strain-rate sensitivity index was found to increase with decreasing load-hold period, suggesting that the elastic moduli of the amorphous polymers determined by nanoindentation (together with the true contact area) depends significantly on the selection of the load-hold period. The rheological condition of the creeping solid under constant load changes substantially with time to affect the subsequent unloading recovery process. It is therefore advisable to control not only the unloading strain rate but also the load-hold period when testing time-dependent materials.
Publisher: Elsevier BV
Date: 04-2012
Publisher: The Royal Society
Date: 26-10-2011
Abstract: Hard, biological materials are generally hierarchically structured from the nano- to the macro-scale in a somewhat self-similar manner consisting of mineral units surrounded by a soft protein shell. Considerable efforts are underway to mimic such materials because of their structurally optimized mechanical functionality of being hard and stiff as well as damage-tolerant. However, it is unclear how different hierarchical levels interact to achieve this performance. In this study, we consider dental enamel as a representative, biological hierarchical structure and determine its flexural strength and elastic modulus at three levels of hierarchy using focused ion beam (FIB) prepared cantilevers of micrometre size. The results are compared and analysed using a theoretical model proposed by Jäger and Fratzl and developed by Gao and co-workers. Both properties decrease with increasing hierarchical dimension along with a switch in mechanical behaviour from linear-elastic to elastic-inelastic. We found Gao's model matched the results very well.
Publisher: AIP Publishing
Date: 15-03-1998
DOI: 10.1063/1.367108
Abstract: The effects of 50 keV H+ and Ar+ ions on the mechanical properties and ultraviolet-visible absorption of the polymer CR39 were investigated. It was found that the H+ implantation produced a yellow–brown material with optical properties similar to amorphous hydrogenated carbon, whereas Ar+ implantation produced a material with optical properties more like evaporated amorphous carbon. The mechanical properties of the implanted material were measured using a nanoindentation technique and increases in both the elastic modulus and hardness (maximum sustainable contact pressure) were observed following irradiation with both ion species. Compared to Ar+ implantation, H+ implantation of CR39 was found to produce a more transparent material at an equivalent maximum sustainable contact pressure and therefore H+ ions were found to be more desirable than Ar+ ions for the treatment of CR39 optical components.
Publisher: Elsevier BV
Date: 12-2001
DOI: 10.1016/S0142-9612(01)00062-X
Abstract: Using the single-edge notched bending (SENB) test, two fracture toughness parameters of longitudinal and transverse bovine bone specimens were evaluated: the critical stress intensity factor, Kc, determined from the peak load to initiate fracture, and the energy or work of fracture, Wf, the energy required to extend a crack through a notched specimen. It was found that preservation of bone in alcohol resulted in a 25-45% higher Kc value compared to control specimens stored in physiological saline whereas the work of fracture, Wf, demonstrated the opposite behaviour, with the alcohol stored specimens having a 28-56% lower value than the saline control specimens. It was established that the effect of alcohol is reversible upon the bone being restored in saline. Consistent with previous studies, it was found that cracks oriented in the longitudinal direction resulted in both a significantly lower fracture toughness and lower work of fracture than those cracks directed transversely. The results are discussed in terms of the proposed deformation and fracture mechanisms known to occur in bone.
Publisher: Wiley
Date: 02-1994
Publisher: Elsevier BV
Date: 2005
DOI: 10.1016/J.JDENT.2004.07.001
Abstract: The aim of the investigation was to assess the influence of sandblasting, grinding, grinding orientation, polishing and heat treatment on the flexural strength of a yittria stabilized tetragonal zirconia polycrystals ceramic (Y-TPZ). The specimens (160 beams) were equally ided into four groups according to the surface treatment (sandblasted, polished, ground parallel to the tensile axis, ground perpendicular). Twenty specimens from each group underwent heat treatment under the firing conditions used to fire a layer of porcelain and glaze. After treatment, the three-point flexure test was used to calculate the flexural strength and X-ray diffraction analysis was used to estimate the relative amount of monoclinic phase. The reliability of strength was assessed through the Weibull distribution. Statistical analysis was conducted with multiple regression analysis, one-way ANOVA and Tukey's pairwise multiple comparisons. Treated and fractured surfaces were observed with SEM. The following values of strength and relative content of monoclinic phase of zirconia were measured for each group: sandblasted (1540MPa 9.5%) ground parallel (1330MPa 8.3%) ground perpendicular (1525MPa 8.3%) ground parallel and heated (1225MPa monoclinic content not detectable) ground perpendicular and heated (1185MPa monoclinic content not detectable) polished and heated (1165MPa monoclinic content not detectable) polished (1095MPa 0.8%) sandblasted and heated (955MPa 0.3%). The present study suggests that sandblasting and grinding may be recommended to increase the strength of dental Y-TZP, provided they are not followed by heat treatment. Fine polishing may remove the layer of compressive stresses and therefore, lower the mean flexural strength.
Publisher: Springer Science and Business Media LLC
Date: 09-1977
DOI: 10.1007/BF00566254
Publisher: IOP Publishing
Date: 03-09-2010
Publisher: Elsevier BV
Date: 2003
Publisher: Japanese Society for Dental Materials and Devices
Date: 2010
DOI: 10.4012/DMJ.2009-094
Abstract: The purpose of this study was to investigate the properties of a die hardener penetrated layer and evaluate its protective effects on the surface of die stone. A commercial die hardener (PDQ die hardener, Whipmix corp., USA) was tested on a die stone (GC Fujirock EP die stone, GC Europe, Belgium) and a dental plaster (Dental Stone, United States Gypsum Company, USA). Nanoindentation and micro-scratch tests were performed on both coated and uncoated specimens. The scratch damage was observed by SEM and the penetration depth of die hardener was detected by the affiliated EDX. Upon drying, the die hardener penetrated into the die stone to a depth of 3-5 microm, and deposited a thin film on the surface of die stone. Although the die hardener penetrated layer did not show improved mechanical properties, the die hardener film on the surface did protect the specimens from abrasion damage.
Publisher: Springer Science and Business Media LLC
Date: 30-06-2009
DOI: 10.1007/S00455-009-9223-2
Abstract: Bolus propulsion during the normal oral phase of swallowing is thought to be characterised by the sequential elevation of the front, middle, and posterior regions of the dorsum of the tongue. However, the coordinated orchestration of lingual movement is still poorly understood. This study examined how pressures generated by the tongue against the hard palate differed between three points along the midline of the tongue. Specifically, we tested three hypotheses: (1) that there are defined in idual patterns of pressure change within the mouth during liquid swallowing (2) that there are significant negative pressures generated at defined moments during normal swallowing and, (3) that liquid swallowing is governed by the interplay of pressures generated in an anteroposterior direction in the mouth. Using a metal appliance described previously, we measured absolute pressures during water swallows in six healthy volunteers (4 male, 2 female) with an age range of 25-35 years. Participants performed three 10-ml water swallows from a small cup on five separate days, thus providing data for a total of 15 separate water swallows. There was a distinct pattern to the each of the pressure signals, and this pattern was preserved in the mean obtained when the data were pooled. Furthermore, raw signals from the same subjects presented consistent patterns at each of the five testing sessions. In all subjects, pressure at the anterior and hind palate tended to be negative relative to the preswallow value at mid-palate, however, pressure changes were less consistent between in iduals. When the pressure differences between the sites were calculated, we found that during the swallow a net negative pressure difference developed between anterior and mid-palate and a net positive pressure difference developed between mid-palate and hind palate. Large, rapid fluctuations in pressure occurred at all sites and these varied several-fold between subjects. When the brief sharp reduction in pressure that occurred early in each swallow was used to determine the sequence of events, we found that activity occurred first at the anterior of the palate followed by the mid-palate and then the hind palate. There was a considerably longer and more variable delay between the start of activity at the front of the palate than at the rear of the palate. To obtain an index of the "effort" involved in generating the pressures at each site regardless of direction (positive or negative), we obtained the product of the root mean square (RMS) pressure change during each swallow (kPa) and its duration (s). Overall, the most effort appears to have occurred at the front of the palate and the least at mid-palate. Our results also showed that some participants exerted a small amount of midline pressure when swallowing, while others used a relatively large amount of tongue pressure. We conclude that while tongue behaviour during swallowing follows a classical sequence of rapid shape changes intended to contain and then propel the bolus from the oral cavity to the pharynx, there is a large range of in idual variability in how this process is accomplished.
Publisher: FSFEI HE Don State Technical University
Date: 25-12-2020
DOI: 10.23947/2687-1653-2020-20-4-350-359
Abstract: Introduction. When developing ocular prostheses, a number of problems arise, one of which is the construction of the connection between the hard optical part and the soft corneal tissue. Their Young's modules can differ by three orders of magnitude. In this case, the problem arises of creating an intermediate layer, possibly with gradient properties, whose purpose is to exclude injury to soft biological tissues. Two types of keratoprostheses are considered: the first type with a support plate and the second type with an intermediate functionally gradient layer. The stress-strain state of the prosthesis is calculated for the first type. For the second type, analytical and finite element modeling of the interaction of a cylindrical optical prosthesis, an intermediate inhomogeneous layer, and the cornea was carried out in the elastic media. Two versions are considered: discounting the curvature (circular plate or plate) and with account of the curvature (spherical dome or shell). The work objective is to study the stress-strain state of the keraprosthesis and cornea in the contact area. Materials and Methods. Mathematical models of the structures under consideration are the boundary value problems of the linear elasticity theory. The analytical solution is constructed for a simplified model in the form of a composite circular plate. Spatial three-dimensional problems and axisymmetric problems are solved by the finite element method. Finite element modeling of the considered structures was performed in the CAE package ANSYS and ACELAN. Results. CAD models of keratoprostheses with conditions of fixing and loading are constructed. The load acting on the keraprosthesis under the effect of intraocular pressure was determined. The stress-strain state of the keratoprosthesis and cornea elements was calculated. Special attention was paid to the area of its contact with the keratoprosthesis. Discussion and Conclusions. The results of calculating the axial displacements and mechanical stresses in the first type of keratoprosthesis show that the selected geometric parameters meet the kinematic and strength requirements. The proposed models of the deformed state of soft biological tissues provide assessing their injury when using a keratoprosthesis of the second type, as well as selecting the geometric parameters and gradient properties of the intermediate layer.
Publisher: Wiley
Date: 16-05-1970
Publisher: Wiley
Date: 12-2013
Publisher: Elsevier BV
Date: 09-1994
Publisher: Elsevier BV
Date: 12-1994
Publisher: Wiley
Date: 08-1989
Publisher: Springer Science and Business Media LLC
Date: 2002
Publisher: Elsevier BV
Date: 04-2013
DOI: 10.1016/J.JMBBM.2012.08.019
Abstract: Rapid and stable osseointegration signifies a major concern in design of implantable prostheses, which stimulates continuous development of new implant materials and structures. This study aims to develop a graded configuration of a bead article coated porous surface for implants by exploring how its micromechanical features determine osseointegration through multiscale modeling and remodeling techniques. A typical dental implantation setting was exemplified for investigation by using the remodeling parameters determined from a systematic review of bone-implant-contact (BIC) ratio published in literature. The global responses of a macroscale model were obtained through 48 month remodeling simulation, which forms the basis for the 27 microscopic models created with different particle gradients ranging from 30 to 70μm. The osseointegration responses are evaluated in terms of the BIC ratio and the averaged 10% peak Tresca shear stress (PTS). Within the s ling designs considered, the configuration with 50-30-30μm particle sizes provides the best outcome, counting 20% more BIC ratio and 0.17MPa less PTS compared with the worst case scenario, also outperforming the best uniform morphology of 70μm particles. Furthermore, the response surface method (RSM) was utilized to formulate the bone remodeling responses in terms of gradient parameters across three layers. Gradient 30.0-30.0-32.1 is found an optimal gradient for BIC ratio, and 70-45.4-40.8 the best for the minimum PTS. The multiobjective optimization was finally performed to simultaneously maximize BIC ratio and minimize PTS for achieving the best possible overall outcome. Due to strong competition between these two design objectives, a Pareto front is generated. To make a proper trade-off, the minimum distance selection criterion is considered and the gradient of 37.1-70.0-67.7 appears an optimal solution. This study provides a novel surface configuration and design methodology for in idual patient that allow optimizing topographical gradient for a desirable patient-specific biomechanical environment to promote osseointegration.
Publisher: Wiley
Date: 03-1986
Publisher: Elsevier BV
Date: 12-2007
DOI: 10.1016/J.DENTAL.2007.02.002
Abstract: It is still largely unknown as to what material parameter requirements would be most suitable to minimise the fracture and maximising the retention rate of the restoration of cervical non-carious lesions (NCCL). The present paper, as a first of its kind, proposes a radical approach to address the problems of material improvement, namely: numerical-based, fracture and damage mechanics materials optimisation engineering. It investigates the influence of the elastic modulus (E) on the failure of cervical restorative materials and aims to identify an E value that will minimise mechanical failure under clinically realistic loading conditions. The present work relies on the principle that a more flexible restorative material would partially buffer the local stress concentration. We employ a "most favourable" parametric analysis of the restorative's elastic modulus using a fracture mechanics model embedded into finite element method. The advanced numerical modelling adopts a Rankine and rotating crack material fracture model coupled to a non-linear analysis in an explicit finite element framework. The present study shows that the restorative materials currently used in non-carious cervical lesions are largely unsuitable in terms of resistance to fracture of the restoration and we suggest that the elastic modulus of such a material should be in the range of 1GPa. We anticipate that the presented methodology would provide more informative guidelines for the development of dental restorative materials, which could be tailored to specific clinical applications cognisant of the underlying mechanical environment.
Publisher: Elsevier BV
Date: 12-2007
DOI: 10.1016/J.DENTAL.2007.02.003
Abstract: As a typical non-carious cervical lesion, abfraction is a common clinical occurrence which requires restorative treatment in most patients. Nonetheless, the relatively poor clinical longevity of cervical dental used for restoring abfraction lesions has been a major concern of dentists and patients. The continuing loss of hard tissue and, in turn, the low retention of the restorative materials in situ motivates an in-depth exploration of the failure mechanism of the biomaterials involved. Despite considerable biomechanical relevance, conventional application of linear static finite element analysis (FEA) does not consider the fracture failure process, nor does it provide a quantitative predictive analysis for restorative design. This paper adopts a novel Rankine and rotating crack model to trace the fracture failure process of the cervical restorations. In contrast to the existing linear FEA, this study presents a nonlinear fracture analysis in an explicit finite element framework, which involves an automatic insertion of initial crack, mesh updating for crack propagation and self contact at the cracked interface. The results are in good agreement with published clinical data, in terms of the location of the fracture failure of the simulated restoration and the inadequacy of the dental restoratives for abfraction lesions. The success of the proposed model also demonstrates the potential for the monitoring and prediction of mechanical failure in other brittle biomaterials in a clinical situation.
Publisher: Elsevier BV
Date: 11-1976
Publisher: AIP Publishing
Date: 2008
DOI: 10.1063/1.2827987
Abstract: Recent observations have shown that enamel exhibits creep behavior during indentation. In this paper, we develop a viscous creep model for enamel that considers the basic shape of the apatite crystallites and treats the thin protein layer between the crystallites as a viscous fluid. The approach enables identification of the main flow planes in the anisotropic enamel structure and the influence of the volume fraction of the apatite crystals. Nanoindentation data showing creep are interpreted consistently and viscosities attributed to the protein layer are evaluated.
Publisher: Elsevier BV
Date: 12-1995
Publisher: Springer Science and Business Media LLC
Date: 03-01-2012
DOI: 10.1557/JMR.2011.409
Publisher: Elsevier BV
Date: 12-2016
DOI: 10.1016/J.DENTAL.2016.09.008
Abstract: The objective of the present study was to determine the hardness and adhesion strength at the porcelain to alloy interface. 15 bi-layer porcelain veneered Co-Cr specimens of each alloy group [cast, powder metallurgy (PM), CAD/CAM(CC)] were manufactured. 12 bi-layered specimens were tested using four-point bend strain energy release rate adhesion test. One before and after porcelain firing specimen of each alloy group were nano-indented at the bulk and metal-porcelain interface to determine the mechanical properties. Electron backscatter diffraction was used to determine the microstructure and phase of the indented areas. The results obtained from the four-point bend strain energy release rate test indicated highest adhesion energy of 92.15J/m The adhesion of the alloy to porcelain was found to be inversely related to the hardness of the interfacial layer at the alloy surface. Lower interfacial hardness was found to be accompanied with higher adhesion energy due to the additional plastic energy consumed during crack propagation along the more ductile interface region of the alloy.
Publisher: Springer Science and Business Media LLC
Date: 08-1977
DOI: 10.1007/BF00542808
Publisher: IOP Publishing
Date: 21-10-1978
Publisher: Springer Science and Business Media LLC
Date: 1989
DOI: 10.1007/BF00720242
Publisher: Elsevier BV
Date: 06-2012
DOI: 10.1016/J.DENTAL.2012.02.011
Abstract: To assess the influence of veneer application on fracture behavior, namely failure load and failure mode, of standardized lithium-disilicate-based crowns. Forty molar crowns (IPS e.max Press, IvoclarVivadent) were fabricated in full anatomic (without veneer, 1.5-2.0mm at occlusal surface) and bi-layer (the occlusal surface is 0.7 mm of veneer and 0.8-1.3mm core) contour representing two groups. Crown specimens were seated and adhered on composite resin dies. All specimens were loaded with a 6mm diameter steatite sphere over the central fissure to failure. Failure modes and fractographic patterns were analyzed by optical stereo and scanning electron microscopy (SEM). Fracture loads of the two groups were compared by the t-test, while the failure modes were analyzed by Pearson Chi-square test. There was a statistically significant difference in mean fracture load values (N±S.D.) between full anatomic [(2665.4±759.2)N] and veneered crowns [(1431.1±404.3)N] (p<0.001) and also in failure modes (χ(2)=6.465, p=0.011). Full anatomic crowns mainly showed bulk fracture, whereas veneered specimens predominately showed cohesive veneer and ceramic interface failure (75%) solely cohesive veneer failure (20%) and bulk fracture (5%). Within the limitations of this study, veneer application resulted in significant lower fracture load values compared to full anatomic crowns. Fracture initiated from occlusal fissures near the load application site. A combination of cohesive veneer and ceramic interface failure represents the main failure mode of lithium-disilicate-based bi-layered crowns, whereas full anatomic crowns failed mainly from ceramic bulk fracture at the occlusal fissures.
Publisher: Springer Science and Business Media LLC
Date: 2001
Abstract: The intrinsic benefits of low exotherm and bioactivity have generated interest in utilizing glass-ionomer cements (GIC) as a bone cement replacement in orthopaedic surgery. This paper is concerned with evaluating the mechanical properties of compressive strength, flexural strength, and fracture toughness for two traditional GICs, one resin-modified GIC (an experimental bone cement) and two polymethylmethacrylate (PMMA) cement systems. To determine the suitability of a GIC system for use in the clinical orthopaedic setting, the additional characteristics of setting exotherm and setting time have also been evaluated. The characterization of these two vastly different cement systems has raised some concern as to the applicability of using the current orthopaedic standards for the testing of GIC systems. In particular, issues relating to the strain rate dependence of PMMA cement and the exothermic basis for determining setting time are not applicable as these factors are not characteristic of GIC systems. Whilst the intrinsic benefits of current GIC systems are well understood and generally accepted, this study has shown their intrinsic mechanical properties to be inferior to current PMMA cements. Improvement in the mechanical properties of traditional GICs have been achieved with the addition of a resin component (HEMA).
Publisher: Elsevier BV
Date: 12-1994
Publisher: CSIRO Publishing
Date: 06-02-2023
DOI: 10.1071/PY22178
Abstract: Background The Australian population is aging, and the proportion of older Australians will continue to grow over the coming decades. However, there is a lack of research published on the specific roles and responsibilities of allied health professionals (AHPs) providing palliative care within an aged care context. Understanding the roles and needs of AHPs providing care during the last months of life in the community and aged care facilities could contribute to workforce planning, targeted information and improved care. Methods In total, 108 eSurveys were collected between November 2019 to May 2020 from three allied health professions working in government-funded aged care the majority of these being in residential aged care. Descriptive data are reported on the provision of care in key palliative care domains, care settings and practice activity. Results Nearly all respondents reported they had worked with older Australians who had palliative care needs. However, over one-third of respondents reported low levels of confidence in supporting clients or residents with palliative care needs. The majority indicated they would benefit from additional education and training and support in palliative care. Conclusions This study investigated the role of the allied health workforce in contributing to the care of older Australians at the end of life. It has also demonstrated that there are gaps in practice activity and work role that must be addressed to ensure this workforce can support older people with palliative care needs in receipt of aged care services.
Publisher: AIP Publishing
Date: 27-02-2006
DOI: 10.1063/1.2177364
Abstract: Nanoindentation tests in an 90°-ac-domain area of an {001} orientated barium titanate single crystal were performed using four different indenters (two with cube corner and two with spherical shape) with tip radii from 61nm to 1.9μm. Extensive calibrations of the tips on fused quartz and sapphire defined the penetration depth range for approximately spherical contact prior to indentation of barium titanate (BaTiO3). The measured elastic modulus is independent of the different indenters. The measurements showed plastic deformation after “pop-in”. The calculated mean pressure remained constant for each indenter, but clearly depends upon the indenter radius. The indenter radius dependence of the hardness support the concept of “geometrically necessary dislocations”, proposed by W. D. Nix and H. Gao [J. Mech. Phys. Sol., 46, 411 (1998)] and its extension to spherical tipped indenters [J. G. Swadener, E. P. George, G. M. Pharr, J. Mech. Phys. Solids, 50, 681 (2002)]. The results show this concept fits the data generated with indenter radii which are at least an order of magnitude lower than investigated by Swadener. Furthermore, the results agree with estimates of the statistically stored dislocation density determined for BaTiO3.
Publisher: Elsevier BV
Date: 07-2013
DOI: 10.1016/J.LEGALMED.2013.01.001
Abstract: Despite numerous studies on high impact fractures of ribs, little is known about compressive rib injuries. We studied rib fractures from a biomechanical and morphological perspective using 15, 5th ribs of domestic pigs Sus scrofa, ided into two groups, desiccated (representing post-mortem trauma) and fresh ribs with intact periosteum (representing peri-mortem trauma). Ribs were axially compressed and subjected to four-point bending in an Instron 3339 fitted with custom jigs. Morphoscopic analysis of resultant fractures consisted of standard optical methods, micro-CT (μCT) and scanning electron microscopy (SEM). During axial compression, fresh ribs had slightly higher strength because of energy absorption capabilities of their soft and fluidic components. In flexure tests, dry ribs showed typical elastic-brittle behaviour with long linear load-extension curves, followed by relatively short non-linear elastic (hyperelastic) behaviour and brittle fracture. Fresh ribs showed initial linear-elastic behaviour, followed by strain softening, visco-plastic responses. During the course of loading, dry bone showed minimal observable damage prior to the onset of unstable fracture. In contrast, fresh bone showed buckling-like damage features on the compressive surface and cracking parallel to the axis of the bone. Morphologically, all dry ribs fractured precipitously, whereas all but one of the fresh ribs showed incomplete fracture. The mode of fracture, however, was remarkably similar for both groups, with butterfly fractures predominating (7/15, 46.6% dry and wet). Our study highlights the fact that under controlled loading, despite seemingly similar butterfly fracture morphology, fresh ribs (representing perimortem trauma) show a non-catastrophic response. While extensive strain softening observed for the fresh bone does show some additional micro-cracking damage, it appears that the periosteum may play a key role in imparting the observed pseudo-ductility to the ribs. The presence of fibrous pull-out and grooving of the outer tensile surface associated with periosteal stretching suggests that the periosteum under tension is able to sustain very high strain and bridge the mouth of the extending butterfly crack, thereby contributing to the observed strain-softening behaviour.
Publisher: Springer Science and Business Media LLC
Date: 03-2009
Publisher: Elsevier BV
Date: 05-2004
DOI: 10.1016/J.BIOMATERIALS.2003.08.056
Abstract: The influence of processing-introduced flaws and heat treatment on the strength degradation of the dental core material has recently been observed. However, there are insufficient studies which investigate the role of grinding, grinding orientation, sandblasting, polishing and heat treatment on the strength of In-Ceram Alumina (IA), one of the most used glass-infiltrated alumina-reinforced dental core ceramics. To address these issues, the uniaxial flexural strength and reliability of eight groups of specimens (sandblasted, ground parallel to the tensile axis, ground perpendicular, and polished with and without heat treatment) were assessed. Statistical analyses indicate that heat treatment significantly improved the flexural strength of the material regardless of the surface treatment. Conversely, any surface treatment caused strength degradation, if it was not followed by heat treatment. Sandblasting caused the most marked strength degradation. Polishing alone (without heat treatment) did not strengthen the ceramic. The orientation of grinding in respect of the direction of the tensile stresses did not influence the ultimate tensile strength. The present study suggests that, in the case of IA, sandblasting, grinding and polishing should always be followed by heat treatment in order to avoid strength degradation of the material.
Publisher: Elsevier BV
Date: 05-2009
DOI: 10.1016/J.JBIOMECH.2009.02.004
Abstract: Tooth enamel is the stiffest tissue in the human body with a well-organized microstructure. Developmental diseases, such as enamel hypomineralisation, have been reported to cause marked reduction in the elastic modulus of enamel and consequently impair dental function. We produce evidence, using site-specific transmission electron microscopy (TEM), of difference in microstructure between sound and hypomineralised enamel. Built upon that, we develop a mechanical model to explore the relationship of the elastic modulus of the mineral-protein composite structure of enamel with the thickness of protein layers and the direction of mechanical loading. We conclude that when subject to complex mechanical loading conditions, sound enamel exhibits consistently high stiffness, which is essential for dental function. A marked decrease in stiffness of hypomineralised enamel is caused primarily by an increase in the thickness of protein layers between apatite crystals and to a lesser extent by an increase in the effective crystal orientation angle.
Publisher: Wiley
Date: 09-1981
Publisher: Elsevier BV
Date: 1991
Publisher: Japanese Society for Dental Materials and Devices
Date: 1994
DOI: 10.4012/DMJ.13.220
Abstract: A comparison was made on the mechanical properties of three glass-ionomer cements, one of which was of experimental fiber-reinforcing and auto-curing type. Two others were proprietary auto-curing and light-activating cements. Biaxial flexure test was conducted on disc s les. Three-point bending test was also carried out on bar s les to determine modulus of elasticity and strength. All s les were kept at 37 degrees C and 100% RH for 24 h before testing under ambient conditions. A prolonged fracture process was observed in the experimental cement, demonstrating the effect of fiber incorporation in stabilizing the fracture process. The proprietary cements failed in a brittle manner. Comparison of the mechanical properties identified three characteristics. These were a high Weibull modulus resulting from the stabilization in fracture process, a modulus of elasticity value comparable to that of dentin, and a high biaxial flexure strength close to that of a dental resin composite.
Publisher: Elsevier BV
Date: 09-2016
DOI: 10.1016/J.JMBBM.2016.05.025
Abstract: This study investigated the structural, biomechanical and fractographic features of rib fractures in a piglet model, to test the hypothesis that fist impact, apart from thoracic squeezing, may result in lateral costal fractures as observed in abused infants. A mechanical fist with an accelerometer was constructed and fixed to a custom jig. Twenty stillborn piglets in the supine position were impacted on the thoracic cage. The resultant force versus time curves from the accelerometer data showed a number of steps indicative of rib fracture. The correlation between impact force and number of fractures was statistically significant (Pearson׳s r=0.528). Of the fractures visualized, 15 completely pierced the parietal pleura of the thoracic wall, and 5 had butterfly fracture patterning. Scanning electron microscopy showed complete bone fractures, at the zone of impact, were normal to the axis of the ribs. Incomplete vertical fractures, with bifurcation, occurred on the periphery of the contact zone. This work suggests the mechanism of rib failure during a fist impact is typical of the transverse fracture pattern in the anterolateral region associated with cases of non-accidental rib injury. The impact events investigated have a velocity of ~2-3m/s, approximately 2×10(4) times faster than previous quasi-static axial and bending tests. While squeezing the infantile may induce buckle fractures in the anterior as well as posterior region of the highly flexible bones, a fist punch impact event may result in anterolateral transverse fractures. Hence, these findings suggest that the presence of anterolateral rib fractures may result from impact rather than manual compression.
Publisher: Springer Science and Business Media LLC
Date: 03-2009
Abstract: The aim of the investigation was to study the influence of indenter tip geometry on the conventionally obtained indentation modulus of enamel by nanoindentation. Indentation tests on bovine enamel using three different diamond pyramidal indenters with half face angles 65.27°, 45°, and 35.26° were conducted to evaluate the indentation modulus using the Oliver–Pharr method [W.C. Oliver and G.M. Pharr, J. Mater. Res. 7, 1564 (1992)]. In addition, three different dehydration conditions were studied: wet under Hank's balanced salt solution, laboratory dried, and vacuum dehydrated. For the Berkovich indenter (65.27°) and 45° pyramidal indenters, there was only a small difference between indentation modulus values, whereas for the cube-corner indenter (35.26°) a ratio of 2.4 between laboratory dry and wet s les was found. A detailed evaluation, including indentation creep and recovery as well as pileup, resulted in a reduction of this latter ratio to 1.7. This still large difference was rationalized on the basis of the different deformation mechanisms generated by indenters of different face angles.
Publisher: Elsevier BV
Date: 08-2006
DOI: 10.1016/J.BIOMATERIALS.2006.03.045
Abstract: Nano-indentation with a sharp (Berkovich) and two spherical indenters with nominal tip radii of 5 and 20 microm was used to determine the elastic modulus and stress-strain response of human enamel. Indentation tests were made over a wide range of peak loads from 1 to 450 mN in two orthogonal directions, i.e., parallel and perpendicular to enamel prisms. The elastic modulus and hardness (mean contact pressure) versus depth of penetration were determined for the three indenters. From the spherical indentation data, stress-strain curves (H-tantheta curve) of enamel were determined in the two orthogonal directions and were found to be different. The elastic modulus showed load dependence for both orientations of the enamel rod structure that depended on the indenter. However, these differences could be normalized upon considering the contact diameter. The indented s le was imaged with an SEM to investigate the near surface damage. In conclusion, prism-sheath structure played an important role in determining the mechanical properties as well as the localized fracture of enamel.
Publisher: ASME International
Date: 19-03-2007
DOI: 10.1115/1.2744027
Abstract: Four-point-bending V-notched specimens of lead zirconate titanate (PZT) poled parallel to the long axis are fractured under conditions of controlled crack growth in a custom-made device. In addition to the mechanical loading electric fields, up to 500V∕mm are applied parallel and anti-parallel to the poling direction, i.e., perpendicular to the crack surface. To determine the different contributions to the total energy release rate, the mechanical and the piezoelectric compliance, as well as the electrical capacitance of the s le, are recorded continuously using small signal modulation/demodulation techniques. This allows for the calculation of the mechanical, the piezoelectric, and the electrical part of the total energy release rate due to linear processes. The sum of these linear contributions during controlled crack growth is attributed to the intrinsic toughness of the material. The nonlinear part of the total energy release rate is mostly associated to domain switching leading to a switching zone around the crack tip. The measured force-displacement curve, together with the modulation technique, enables us to determine this mechanical nonlinear contribution to the overall toughness of PZT. The intrinsic material toughness is only slightly dependent on the applied electric field (10% effect), which can be explained by screening charges or electrical breakdown in the crack interior. The part of the toughness due to inelastic processes increases from negative to positive electric fields by up to 100%. For the corresponding nonlinear electric energy change during crack growth, only a rough estimate is performed.
Publisher: Wiley
Date: 08-02-2010
DOI: 10.1111/J.1708-8208.2008.00127.X
Abstract: Soldered or cast bars are used as a standard of care in attachment systems supporting maxillary and mandibular implant overdentures. When failures of these bars occur, currently there is a lack of evidence in relation to their specific etiology, location, or nature. To investigate the failure process of a case series of six failed soldered bars, four intact soldered bars, and one intact cast milled bar, which had been supporting implant overdentures. A total of 11 different overdenture bars were removed from patients with different configuration of opposing arches. A failed bar (FB) group (n = 6) had failed soldered overdenture bars, which were recovered from patients following up to 2 years of wear before requiring prosthodontic maintenance and repair. An intact bar (IB) group (n = 5) had both soldered bars and a single cast milled bar, which had been worn by patients for 2 to 5 years prior to receiving other aspects of prosthodontic maintenance. All bars were examined using scanning electron microscopy to establish the possible mode of failure (FB) or to identify evidence of potential failure in the future (IB). Evidence of a progressive failure mode of corrosion fatigue and creep were observed on all the FB and IB usually around the solder areas and nonoxidizing gold cylinder. Fatigue and creep were also observed in all the IB. Where the level of corrosion was substantial, there was no evidence of wear from the matrices of the attachment system. Evidence of an instantaneous failure mode, ductile and brittle overload, was observed on the fracture surfaces of all the FB, within the solder and the nonoxidizing gold cylinders, at the solder/cylinder interface. Corrosion, followed by corrosion fatigue, appears to be a key factor in the onset of the failure process for overdenture bars in this case series of both maxillary and mandibular overdentures. Limited s le size and lack of standardization identify trends only but prevent broad interpretation of the findings.
Publisher: Elsevier BV
Date: 02-2014
DOI: 10.1016/J.DENTAL.2013.11.001
Abstract: This in vitro study was designed to investigate the influence of the veneer and cyclic loading on the failure behavior of lithium disilicate glass-ceramic (LDG) crowns on maxillary first molar. Sixty-four LDG crowns were ided into 4 groups (n=16). Thirty-two monolithic crowns were fabricated from IPS e.max Press (M), and the remaining bilayered crowns using cut-back technique and conventional manual layering technique from IPS e.max Press/Ceram (B). Monolithic or bilayered crowns were subjected to single-load-to-fracture (SLF) testing using a universal testing machine, before (M1 and B1) and after exposure to sliding-contact fatigue (SCF) testing (M2 and B2), consisting of 1,200,000 mechanical cycles (Fmax=98 N). Data were statistically analyzed using two-by-two factorial design ANOVA. Fractographic analysis was performed to determine the fracture modes of the failed specimens. The mean fracture load values (N±S.D.) for M1, B1, M2 and B2 were 2686±628 N, 1443±327 N, 2133±578 N and 1464±419 N, respectively. Significant differences were found between the failure loads of all groups (P<0.001), except between groups B1 and B2. Bulk fracture initiating from the occlusal surface is the primary failure mode of monolithic and veneered LDG crowns. Cracking that initiated from core-veneer interfacial defects and ultimately resulted in bulk fracture is another major failure origin of veneered all-ceramic crowns. Veneer application resulted in significantly lower fracture load values compared to monolithic LDG crowns. Cyclic loading is an accelerating factor contributing to fracture for monolithic LDG crowns but not for bilayered ones.
Publisher: Wiley
Date: 20-12-2012
Publisher: Emerald
Date: 03-2004
DOI: 10.1108/00070700410528772
Abstract: From the 1970s onwards, studies of the dynamics involved in family food provisioning in Britain and the USA have provided consistent evidence of the centrality of husbands and male breadwinners to food decisions. Recent studies are beginning to show the significance of children or the “junior consumer” to household food decisions. This paper reports on focus groups conducted in Australia in the mid‐1990s that support the argument that children exert considerable influence over family diets. One obvious reason for this trend lies in the activities of food retailers and advertisers/marketers, who target their goods, services and messages to children. These marketplace actors are encouraging children to identify as consumers. A less obvious explanation, and the one explored in this paper, concerns changing parenting practices. Despite the double workload of many family food providers, children's demands are being responded to in unprecedented ways. Metaphorically, children are displacing male adults at the head of the table. The paper comments on the consequences of children's dominance over dietary practices.
Publisher: Quintessence Publishing
Date: 11-2016
DOI: 10.11607/IJP.4726
Abstract: The objective of this clinical study was to determine the relationship of mandibular morphology with residual ridge resorption (RRR) of implant-retained overdenture (IRO) patients. RRR was quantified as change in bone volume over 1- and 2-year periods using cone beam computed tomography and a medical imaging program. Features of the mandibular morphology, namely the gonial angle, ramus length, ramus width, corpus length, and corpus height, were measured on three-dimensional models and correlated to the RRR. A total of 25 participants were treated with mandibular IROs opposing maxillary complete dentures. By the 2-year follow-up, radiographic data for 18 patients were complete for analysis. Of these 18 participants, half fall into the low gonial angle category and the other half into the high angle. The extent of RRR was highly variable among participants and ranged from -2 to +2 mm in depth over the 2-year period. The mean decrease in bone volume after the first year was 3.8 ± 4.5%. This rate decreased to 3.2 ± 4.1% after the second year. RRR occurs either by translation of the entire thickness of cortical layer apically or by thinning of the outer cortical layer. RRR was significantly correlated to gonial angle (r = .471 P = .048) and predominantly occurred in the molar region in low-angle participants and more anteriorly in high-angle participants. There was no association between RRR and ramus length (r = -.341 P = .166), ramus width (r = -.183 P =.468), corpus length (r = .057 P = .821), and corpus height (r = .097 P = .702). Within the limitations of this study, it may be concluded that gonial angle is significantly related to RRR associated with IROs.
Publisher: Wiley
Date: 05-1979
Publisher: Elsevier BV
Date: 2021
Publisher: AIP Publishing
Date: 04-12-2000
DOI: 10.1063/1.1332110
Abstract: Spherical indentation of crystalline silicon has been studied using cross-sectional transmission electron microscopy (XTEM). Indentation loads were chosen below and above the yield point for silicon to investigate the modes of plastic deformation. Slip planes are visible in the XTEM micrographs in both indentation loads studied. A thin layer of polycrystalline material has been identified (indexed as Si-XII from diffraction patterns) on the low-load indentation. The higher-load indentation revealed a large region of amorphous silicon. The sequence of structural deformation by indentation in silicon has been observed with the initial deformation mechanism being slip until phase transformations can take place.
Publisher: Elsevier BV
Date: 05-2007
DOI: 10.1016/J.ARCHORALBIO.2006.10.020
Abstract: A common feature of studies of mandibular morphology is the assumption that there is some functional relation between the form of the lower jaw and masticatory stress. It was noted that the local variation in cortical bone thickness in the mandibular corpus appears to be stereotypical among anthropoids. This occurs at sections under the molars, where the lingual cortical plate is thinner than buccal one. In this study we investigate and contrast the strain pattern along buccal and lingual surfaces of the mandibular corpus during mastication using a numerical model of a human mandible. We show that strain distribution differs in alveolar and mid-corpus segments of the mandible and that the latter develops an alternate pattern between the buccal and lingual aspects of the working and balancing sides of the jaw. We then relate the magnitude of these strains to Frost's mechanostat. Our results suggest that the cortical asymmetry of the human mandible is in fact not related to strain patterns generated during mastication.
Publisher: Elsevier BV
Date: 03-2016
DOI: 10.1016/J.JMBBM.2015.10.018
Abstract: Attempts to understand the mechanical behavior of dentin and other mineralized tissues have been primarily focused on the role of their more abundant matrix components, such as collagen and hydroxyapatite. The structural mechanisms endowing these biological materials with outstanding load bearing properties, however, remain elusive to date. Furthermore, while their response to deformation has been extensively studied, mechanisms contributing to their recovery from induced deformation remain poorly described in the literature. Here, we offer novel insights into the participation of proteoglycans (PG) and glycosaminoglycans (GAG) in regulating the nanoindentation creep deformation and recovery of mineralized and demineralized dentin. Accordingly, after the enzymatic digestion of either PGs and associated GAGs or only GAGs, the nanoindentation creep deformation of dentin increased significantly, while the relative recovery of both the mineralized and demineralized dentin dropped by 40-70%. In summary, our results suggest that PGs and GAGs may participate in a nanoscale mechanism that contributes significantly to the outstanding durability of dentin and possibly other mineralized tissues of similar composition.
Publisher: Wiley
Date: 1969
Publisher: SAGE Publications
Date: 20-02-2015
Abstract: While nuclear medicine has been proven clinically effective for examination of the change in bone turnover as a result of stress injury, quantitative correlation between tracer uptake and mechanical stimulation in the human jawbone remains unclear. This study aimed to investigate the relationship between bone metabolism observed by 18F-fluoride positron emission tomography (PET) images and mechanical stimuli obtained by finite element analysis (FEA) in the residual ridge induced by the insertion of a removable partial denture (RPD). An 18F-fluoride PET/CT (computerized tomography) scan was performed to assess the change of bone metabolism in the residual ridge under the denture before and after RPD treatment. Corresponding patient-specific 3D finite element (FE) models were created from CT images. Boundary conditions were prescribed by the modeling of condylar contacts, and muscular forces were derived from the occlusal forces measured in vivo to generate mechanobiological reactions. Different mechanobiological stimuli, e.g., equivalent von Mises stress (VMS), equivalent strain (EQV), and strain energy density (SED), determined from nonlinear FEA, were quantified and compared with the standardized uptake values (SUVs) of PET. Application of increased occlusal force after RPD insertion induced higher mechanical stimuli in the residual bone. Accordingly, SUV increased in the region of residual ridge with higher mechanical stimuli. Thus, with SUV, a clear correlation was observed with VMS and SED in the cancellous bone, especially after RPD insertion (R 2 0.8, P 0.001). This study revealed a good correlation between bone metabolism and mechanical stimuli induced by RPD insertion. From this patient-specific study, it was shown that metabolic change detected by PET in the loaded bone, in a much shorter duration than conventional x-ray assessment, is associated with mechanical stimuli. The nondestructive nature of PET/CT scans and FEA could potentially provide a new method for clinical examination and monitoring of prosthetically driven bone remodeling.
Publisher: Wiley
Date: 23-08-2010
Publisher: Elsevier BV
Date: 1993
Publisher: Elsevier BV
Date: 09-2004
Publisher: Elsevier BV
Date: 11-1985
Publisher: Springer Science and Business Media LLC
Date: 10-1982
DOI: 10.1007/BF00724865
Publisher: Springer Science and Business Media LLC
Date: 04-1985
DOI: 10.1007/BF01026313
Publisher: Elsevier BV
Date: 05-2013
DOI: 10.1016/J.DENTAL.2013.03.012
Abstract: To test the hypothesis that the difference in the coefficient of thermal contraction of the veneering porcelain above (αliquid) and below (αsolid) its Tg plays an important role in stress development during a fast cooling protocol of Y-TZP crowns. Three-dimensional finite element models of veneered Y-TZP crowns were developed. Heat transfer analyses were conducted with two cooling protocols: slow (group A) and fast (groups B-F). Calculated temperatures as a function of time were used to determine the thermal stresses. Porcelain αsolid was kept constant while its αliquid was varied, creating different Δα/αsolid conditions: 0, 1, 1.5, 2 and 3 (groups B-F, respectively). Maximum (σ1) and minimum (σ3) residual principal stress distributions in the porcelain layer were compared. For the slowly cooled crown, positive σ1 were observed in the porcelain, orientated perpendicular to the core-veneer interface ("radial" orientation). Simultaneously, negative σ3 were observed within the porcelain, mostly in a hoop orientation ("hoop-arch"). For rapidly cooled crowns, stress patterns varied depending on Δα/αsolid ratios. For groups B and C, the patterns were similar to those found in group A for σ1 ("radial") and σ3 ("hoop-arch"). For groups D-F, stress distribution changed significantly, with σ1 forming a "hoop-arch" pattern while σ3 developed a "radial" pattern. Hoop tensile stresses generated in the veneering layer during fast cooling protocols due to porcelain high Δα/αsolid ratio will facilitate flaw propagation from the surface toward the core, which negatively affects the potential clinical longevity of a crown.
Publisher: AIP Publishing
Date: 15-06-2009
DOI: 10.1063/1.3151967
Abstract: There is considerable controversy over the deformation behavior of germanium (Ge) under nanoindentation using a sharp diamond tip, with a erse range of observations that suggest competing mechanisms. Here we show the deformation mechanism of Ge can be controlled by the rate of applied load. Loading rate is varied over three orders of magnitude using depth-sensing nanoindentation. At slow loading rates, shear-induced plasticity is observed. At rapid loading rates (& mN s−1), pressure-induced phase transformations are detected by ex situ micro-Raman spectroscopy and transmission electron microscopy. This switch in the deformation mechanism is due to the differing rate sensitivities of the respective deformation modes, shear-induced plasticity or pressure-induced phase transformation.
Publisher: Public Library of Science (PLoS)
Date: 10-07-2015
Publisher: AIP Publishing
Date: 02-05-2005
DOI: 10.1063/1.1920410
Abstract: Nanoindentation tests in an aa-in-plane domain area of an {001} oriented barium titanate single crystal were performed using a conical indenter with a tip radius of 800 nm. The topography and the polarization vectors of the area after indentation were imaged afterwards by both atomic force and piezoresponse force microscopy (PFM), respectively. Two perpendicular oriented cracks in the {110} planes were identified in the topographic image. An unexpected considerable uplift occurs inside the residual impression, which was correlated with a sharp pop-out-like behavior observed in the force-displacement curve just prior to unloading. Furthermore, PFM revealed an almost a twofold symmetric arrangement of the domains around the indent, which can be explained by residual circumferential tensile stresses around a residual impression and was unambiguously correlated to the crystal orientation.
Publisher: IOP Publishing
Date: 30-09-2008
Publisher: Elsevier BV
Date: 09-2014
DOI: 10.1016/J.PROSDENT.2013.11.012
Abstract: A validated universal method requiring no human input is needed to capture and evaluate preparation geometries in a manner that can be used to see the correlation of different parameters. The purpose of this study was to present a method of capturing and evaluating crown preparation geometry. One manually machined acrylic resin block and 9 randomly selected preparations for ceramic complete crowns prepared by general dentists were selected and prepared. The specimens were scanned (3D scanner Nobel Biocare), and buccolingual and mesiodistal cross section images were collected. The images were imported into digitizing software (Engauge Digitizer 4.1) to convert the outlines into x and y coordinates. Six points were chosen by using a set of algorithms, and the resulting parameters were calculated. The acrylic resin block was milled with a 12 degree total occlusal convergence (TOC) instrument producing a 12.83 degree TOC. For the other specimens, average TOC values ranged from 18 degrees to 52 degrees. The mean average margin width was 0.70 mm, and the mean average base dimension was 6.23 mm. The surface area/volume ratio, resistance length, and limiting taper were also calculated. The method described provides a basis for accurately evaluating preparation geometry without human input.
Publisher: Elsevier BV
Date: 05-2014
DOI: 10.1016/J.JBIOMECH.2014.02.030
Abstract: While orthodontic tooth movement (OTM) gains considerable popularity and clinical success, the roles played by relevant tissues involved, particularly periodontal ligament (PDL), remain an open question in biomechanics. This paper develops a soft-tissue induced external (surface) remodeling procedure in a form of power law formulation by correlating time-dependent simulation in silico with clinical data in vivo (p<0.05), thereby providing a systematic approach for further understanding and prediction of OTM. The biomechanical stimuli, namely hydrostatic stress and displacement vectors experienced in PDL, are proposed to drive tooth movement through an iterative hyperelastic finite element analysis (FEA) procedure. This algorithm was found rather indicative and effective to simulate OTM under different loading conditions, which is of considerable potential to predict therapeutical outcomes and develop a surgical plan for sophisticated orthodontic treatment.
Publisher: Wiley
Date: 04-1985
Publisher: Japan Society of Mechanical Engineers
Date: 2010
DOI: 10.1299/JBSE.5.2
Publisher: AIP Publishing
Date: 23-04-2007
DOI: 10.1063/1.2450649
Abstract: Teeth survive millions of contact cycles with relatively limited damage and wear, despite high local contact stresses. In this letter, the authors investigated the influence of enamel microstructure and specifically the role of the minor protein component on contact induced deformation. They assume that protein is responsible for the nonlinear contact stress-strain relationship. The extremely low contact stresses to induce inelastic contact deformation result in high contact induced energy loss which is indenter geometry dependent. A simple model shows that shear strain in protein layer is 16 times higher than the contact strain, and is where most deformation is dissipated.
Publisher: Elsevier BV
Date: 10-2009
Publisher: Elsevier BV
Date: 2012
DOI: 10.1016/J.JDENT.2011.10.003
Abstract: Comparative studies of bone remodelling and mechanical stresses between inlay and onlay fixed partial dentures (FPD) are rather limited. The purpose of this paper was to evaluate the biological consequence in posterior mandibular bone and the mechanical responses in these two different prosthetic configurations. Three-dimensional (3D) finite element analysis (FEA) models are created to explore the mechanical responses for the inlay and onlay preparations within the same oral environment. Strain induced bone remodelling was simulated under mastication. The remodelling adopted herein relates the strain in the bone to the change of Hounsfield Unit (HU) value in proportion to the surface area density (SAD) of bony morphology, which allows directly correlating to clinical computerised tomography (CT) data. The results show that both FPD designs exhibit a similar resultant change in bone mineral density (BMD) though the onlay configuration leads to a more uniform distribution of bone density. The inlay design results in higher mechanical stresses whilst allowing preservation of healthy tooth structure. This study provides an effective means to further clinical assessment and investigation into biomechanical responses and long-term restorative outcome with different FPD designs. Quantifying in vivo stress distributions associated with inlay/onlay FPDs can further supplement clinical investigations into prosthetic durability, FPD preparation techniques (i.e., taper angles, material development), consequent stress distributions and the ongoing biomechanical responses of mandibular bone.
Publisher: Wiley
Date: 17-03-2006
DOI: 10.1111/J.1600-9657.2006.00427.X
Abstract: The manufacture of laminated-type mouthguards requires skill in fusing sheets of mouthguard materials together. Adequate adhesive strength is required to use mouthguards in a stable condition for a long time. Therefore, in this study, the exfoliation test was applied and some treating techniques and conditions that improve the adhesive strength on a laminated surface were examined. S les were laminated with two pieces of mouthguard material (3 mm thickness) having an adhesive area of 5 x 5 mm2, and whose other end was the holding part. The experimental factors used were as follows: heating time, use of solvent, elimination and direct heating of the laminate surface, colour of materials and water sorption. The result was measured at the time of breakage of the maximum load (N) and the form of destruction was examined. At 165 s of heating time, material failure was shown at under a load exceeding 5.0 N when compared to an untreated condition. Material failure was measured when a solvent was used and during the elimination of the laminated surface at a heating time of 150 s, which is 15 s lesser than in an untreated condition. Material failure was also measured by direct heating on the bonding surface of a second sheet of material at a heating time of 135 s, which is 30 s lesser than in an untreated condition. The differences in colour of the materials influence adhesion. Clear and light coloured materials showed higher adhesion ability. One-way analysis of variance confirmed a statistically significant difference in heating time differences, usage of solvent, elimination, direct heating on bonding surface and colour (P < 0.05). The decrease of adhesive strength by water sorption at 23 degrees and 37 degrees C was not observed significantly. Maximal laminated bond strength can be obtained by minimal heating time and proper treatment with the use of solvent, elimination and direct heating on bonding surface. The differences in the colour of the materials influenced adhesion. Clear and light coloured materials showed higher adhesive ability. Water sorption did not affect the adhesive strength. Therefore, if laminated-type mouthguards were manufactured properly, it can be used for a longer time and in a good condition.
Publisher: Elsevier BV
Date: 11-2007
DOI: 10.1016/J.ACTBIO.2007.05.007
Abstract: Developmental defects in dental enamel pose significant clinical challenges which have highlighted our limited understanding of the structure and properties of this tissue. In this study, we first investigated the contact-size dependence of the physical properties of sound and hypomineralized enamel, and then examined the microstructure to establish a structural basis for their differing properties. Depth-sensing indentation tests were carried out over a wide range of peak loads in a direction perpendicular to the enamel prisms. Hypomineralized enamel demonstrated stronger penetration dependence for measured hardness and elastic modulus than sound enamel. The microstructure of sound and hypomineralized enamel was observed using field emission scanning electron microscopy and transmission electron microscopy with support of a focused ion beam milling system. Images of sound enamel showed barely distinguishable sheath regions with minimal organic presence. In contrast, hypomineralized enamel showed thicker sheath structures surrounding the prisms and higher levels of organic content within both the prisms and the sheath regions. It is argued that the higher organic content within prism structure was responsible for an initial lower hardness and elastic modulus of hypomineralized enamel under low-load indentation. As the indentation depth increased, the thicker organic-rich sheath regions played a more important role in reducing the mechanical properties of the hypomineralized enamel. On the basis of Spears finite element model [Spears IR. A three-dimensional finite element model of prismatic enamel: a re-appraisal of the data on the Young's modulus of enamel. J Dental Res 1997 76(10):1690-97], elastic moduli of sound and hypomineralized enamel were predicted, which matched experimental results.
Publisher: Springer Science and Business Media LLC
Date: 06-1995
Abstract: In the determination of mechanical properties by ultra-microindentation, various errors can appear. This paper analyzes various sources of errors in estimation of elastic modulus and hardness. These errors arise from uncertainties of the indenter geometry and properties, as well as measuring instrument limitations and errors, such as the minimum detectable load, compliance, and noise of the system. Other sources of errors are thermal drift, shape of the impression, and scatter of properties of the tested material. Characteristic features and the magnitude of in idual kinds of errors are discussed, together with formulas and recommended methods for their reduction.
Publisher: Elsevier BV
Date: 09-2004
Publisher: Elsevier BV
Date: 07-2018
DOI: 10.1016/J.ACTBIO.2018.04.049
Abstract: Adhesion plays a major role in the bonding of dental materials. In this study the adhesion of two glass-ceramic systems (IPS e.max and VITABLOCS) to a zirconia sintered substrate using a glass (for IPS e.max) and resin (VITABLOCS) before and after exposure to ageing for 14 days in distilled water at 37 °C are compared using two interfacial fracture mechanics tests, the 3 point bend Schwickerath (Kosyfaki and Swain, 2014 Schneider and Swain, 2015) and 4 point bend (Charalambides et al., 1989) approaches. Both tests result in stable crack extension from which the strain energy release rate (G, N/m or J/m The present study uses a novel approach to investigate the role of ageing or environmental degradation on the adhesive bonding of two dental ceramics to zirconia. This continues to be a major clinical problem but current approaches, till now, have relied upon a myriad of strength based tests to quantify the extent of environmental degradation with time. In this paper we use two fracture mechanics approaches, based upon simple 3 and 4 point bend testing procedures that enable stable debonding crack extension to occur. The paper provides a more critical approach to evaluate the role of environmental degradation of adhesion for dental materials.
Publisher: Hindawi Limited
Date: 04-05-2021
DOI: 10.1155/2021/6688521
Abstract: Purpose. To investigate the effect of minidental implant location on strain distributions transmitted to tooth abutments and dental minidental implants under mandibular distal extension removable partial denture. Materials and Methods. A mandibular Kennedy Class I distal extension model missing teeth 35–37 and 45–47 was constructed. Six dental mini-implants were placed at positions A, B, and C, where position A was 6.5 mm distal to the abutment teeth with 5 mm between each position. Fourteen uniaxial strain gauges were bonded on the model at the region of dental mini-implant and abutment (first premolar). Four groups were designated according to the location of the mini-implants. A load of 150 N and 200 N was applied using an Instron testing machine. Loadings consisted of bilateral and unilateral loading. Comparisons of the mean microstrains among all strain gauges in all situations were analyzed. Results. Variation in mini-implant locations induced local strains in different areas. Strains at the tooth abutment were significantly decreased in the group in which implants were placed mesially. Strains around the mini-implants showed different patterns when loaded with different loading conditions. The group in which implants were placed distally showed the lowest strains compared to other groups. Conclusion. Mesially placed mini-implants showed the lowest strain around abutment teeth, while a distally-placed mini-implants presented the lowest strain around mini-implants themselves. Under favorable biting force, mini-implant is an option to assist mandibular distal extension removable partial denture. Mesially placed mini-implants are recommended when the abutment has periodontally compromised conditions and a distally placed mini-implant when periodontal conditions are stable.
Publisher: Elsevier BV
Date: 1995
Publisher: British Institute of Radiology
Date: 03-2016
Publisher: Wiley
Date: 23-05-2005
DOI: 10.1002/JBM.B.30233
Abstract: An automated 3D finite element (FE) modeling procedure for direct fiber reinforced dental bridge is established on the basis of computer tomography (CT) scan data. The model presented herein represents a two-unit anterior cantilever bridge that includes a maxillary right incisor as an abutment and a maxillary left incisor as a cantilever pontic bonded by adhesive and reinforced fibers. The study aims at gathering fundamental knowledge for design optimization of this type of innovative composite dental bridges. To promote the automatic level of numerical analysis and computational design of new dental biomaterials, this report pays particular attention to the mathematical modeling, mesh generation, and validation of numerical models. To assess the numerical accuracy and to validate the model established, a convergence test and experimental verification are also presented.
Publisher: Elsevier BV
Date: 02-2015
DOI: 10.1016/J.JBIOMECH.2014.11.043
Abstract: Although implant-retained overdenture allows edentulous patients to take higher occlusal forces than the conventional complete dentures, the biomechanical influences have not been explored yet. Clinically, there is limited knowledge and means for predicting localized bone remodelling after denture treatment with and without implant support. By using finite element (FE) analysis, this article provides an in-silico approach to exploring the treatment effects on the oral mucosa and potential resorption of residual ridge under three different denture configurations in a patient-specific manner. Based on cone beam computerized tomography (CBCT) scans, a 3D heterogeneous FE model was created and the supportive tissue, mucosa, was characterized as a hyperelastic material. A measured occlusal load (63N) was applied onto three virtual models, namely complete denture, two and four implant-retained overdentures. Clinically, the bone resorption was measured after one year in the two implant-retained overdenture treatment. Despite the improved stability and enhanced masticatory function, the implant-retained overdentures demonstrated higher hydrostatic stress in mucosa (43.6kPa and 39.9kPa for two and four implants) at the posterior ends of the mandible due to the cantilever effect, than the complete denture (33.4kPa). Hydrostatic pressure in the mucosa signifies a critical indicator and can be correlated with clinically measured bone resorption, pointing to severer mandibular ridge resorption posteriorly with implant-retained overdentures. This study provides a biomechanical basis for denture treatment planning to improve long-term outcomes with minimal residual ridge resorption.
Publisher: Springer Science and Business Media LLC
Date: 10-02-2010
DOI: 10.1007/S10856-010-3988-6
Abstract: The abrasion response of cross sectional areas of enamel was studied by sliding a rounded diamond conical nano-indenter tip across the surface. The nano-indenter tip (radius approximately 1,200 nm) was scanned over a specific squared area with a load of 400 microN. Two different environments were chosen: Hank's balanced salt solution (HBSS) and atmospheric laboratory condition. SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy) were used to characterize the final abraded areas. In addition, single scratches with linear incremented load were performed. The normal load and displacement data were utilized in a complementary manner to support the proposed deformation mechanisms. Greater orientation dependence for the case of the single scratches in relation to the abrasion tests was found. The latter results are discussed in terms of plastic deformation effects. The abrasion mechanisms were found to be the same for both wet and dry measurements and similar to that described in a previous study (Guidoni et al., Wear 266:60-68, 2009 Guidoni, Nano-scale mechanical and tribological properties of mineralized tissues. PhD. Montan University Leoben, Leoben, Austria, 2008). However, scratch deformation under fluid measurements shows greater recovery effects and abrasion resistance.
Publisher: Trans Tech Publications Ltd.
Date: 09-02-2008
Publisher: Elsevier BV
Date: 05-2011
Publisher: Elsevier BV
Date: 09-2013
DOI: 10.1016/J.ACTBIO.2013.05.009
Abstract: Effective and reliable clinical uses of dental ceramics necessitate an insightful analysis of the fracture behaviour under critical conditions. To better understand failure characteristics of porcelain veneered to zirconia core ceramic structures, thermally induced cracking during the cooling phase of fabrication is studied here by using the extended finite element method (XFEM). In this study, a transient thermal analysis of cooling is conducted first to determine the temperature distributions. The time-dependent temperature field is then imported to the XFEM model for viscoelastic thermomechanical analysis, which predicts thermally induced damage and cracking at different time steps. Temperature-dependent material properties are used in both transient thermal and thermomechanical analyses. Three typical ceramic structures are considered in this paper, namely bi-layered spheres, squat cylinders and dental crowns with thickness ratios of either 1:2 or 1:1. The XFEM fracture patterns exhibit good agreement with clinical observation and the in vitro experimental results obtained from scanning electron microscopy characterization. The study reveals that fast cooling can lead to thermal fracture of these different bi-layered ceramic structures, and cooling rate (in terms of heat transfer coefficient) plays a critical role in crack initiation and propagation. By exploring different cooling rates, the heat transfer coefficient thresholds of fracture are determined for different structures, which are of clear clinical implication.
Publisher: Elsevier BV
Date: 08-2000
DOI: 10.1016/S0300-5712(00)00006-3
Abstract: The fracture of bonded ceramic to metal restorations remains a problem in clinical dental practice. The use of resin based composites to repair such fractures is generally unsatisfactory. Tribochemical technology creates a surface layer of small silica particles fused to the surface substrate. Such a layer potentially improves adhesion of resin to both alloy and porcelain. Adhesion between two substrates is traditionally studied using shear or tensile bond strength tests. However, the highest stress at bond failure may not represent the real bonding characteristics correctly. An alternative method is to describe the bonding characteristics by determining the strain energy release rate for a given interface. This study compares the bonding characteristics of a resin to gold orcelain interface using a tribochemical coating process with those of a control group using simple gritblasting. Pre-cracked specimens were subjected to load-unload cycles using a simple four point bending test and the resultant strain energy release rates were calculated. Tribochemically pretreating the porcelain resulted in a significant increase in the resultant strain energy release rate from 42.72+/-3.65J/m(2) for the controls to 61.35+/-6.26J/m(2). Likewise there was a significant improvement in the strain energy release rate for the gold/composite interface from 27.31+/-3.00J/m(2) to 42.13+/-4.83J/m(2). Tribochemical technology offers significant potential advantages for clinical dental practice.
Publisher: Springer Science and Business Media LLC
Date: 13-05-2015
DOI: 10.1007/S00216-015-8742-Y
Abstract: Raman spectroscopy was used to investigate how the effect of pre-treatment protocols, with combinations of hydrochloric acid (HCl), sodium hypochlorite (NaOCl) and hydrogen peroxide (H2O2), for molar-incisor hypo-mineralisation (MIH) altered the penetration depth of polymer infiltrants (ICON, DMG, Hamburg, Germany). Furthermore, the effect on the structure of the MIH portions of the teeth with treatment is examined using multivariate analysis of spectra. It was found that pre-treatment protocols improved penetration depths. The structure of the MIH portion post-treatment appeared much closer to that of normal enamel suggesting a diminution of protein in the MIH region with treatment.
Publisher: Wiley
Date: 08-1990
Publisher: Springer Science and Business Media LLC
Date: 04-2002
Abstract: The mechanical properties of a range of tribological mitigating and biocompatible films deposited on a titanium alloy substrate have been investigated using nanoindentation. For a range of carbon films investigated, the ratio of hardness to modulus was almost constant at around 0.1. The onset of film–substrate interactions of a coated system upon progressive loading could be determined as the depth of penetration at which the slope of the force versus depth curve deviated from that of an analytically derived “bulk film” system that incorporated the indenter tip effect on the contact area. For the carbon-coated systems investigated, the corresponding force, or the critical load-carrying capacity of a localized contact event by a sharp indenter, appears to scale with the elastic modulus mismatch between film and substrate.
Publisher: Elsevier BV
Date: 03-2020
DOI: 10.1016/J.ACTBIO.2019.12.040
Abstract: In this study a high resolution structural analysis revealed that enamel prisms are surrounded by an interface that is discontinuous with frequent mineral to mineral contact separated by gaps. This contact manifests either by crystallites bridging the boundary between prismatic and interprismatic enamel or continuous crystallites curving and bridging the interprismatic enamel to the prisms. The geometrical resolution of this TEM investigation of the interfaces is ≤2 nm as a basis for micromechanical models. Within this resolution, contrary to existing structural descriptions of dental enamel structure in materials science literature, here the crystallites themselves are shown to be either in direct contact with each other, sometimes even fusing together, or are separated by gaps. Image analysis revealed that on average only 57 ± 15% of the interface consists of points of no contact between crystallites. This work reveals structural features of dental enamel that contribute important understanding to both the architecture and mechanical properties of this biological material. A new structural model is proposed and the implications for the mechanical properties of dental enamel are discussed. STATEMENT OF SIGNIFICANCE: In this study a high resolution structural analysis, employing focused ion beam and transmission electron microscopy revealed that enamel prisms are surrounded by interfaces that are discontinuous with frequent mineral to mineral contact separated by gaps. Although the interfaces in enamel have been investigated previously, existing studies are lacking in detail considering the geometry and morphology of the interfaces. We think that this result is of great importance when it comes to the understanding of the mechanical properties. In our opinion the concept of soft sheaths is no longer feasible. The resulting observations are included in a new structural model which provides new qualitative insights into the mechanical behavior. Existing analytical models were applied to simulate the new geometrical structure.
Publisher: Oxford University Press (OUP)
Date: 13-03-2007
DOI: 10.1093/NAR/GKM079
Publisher: Elsevier BV
Date: 05-2003
DOI: 10.1016/S0300-5712(03)00045-9
Abstract: Understanding the mechanical properties of dentine is of importance as adhesive restorative materials mainly achieve their bonding to the tooth structure through dentine. The current study measures the hardness and modulus of elasticity of primary molar dentine using an Ultra-Micro-Indentation System (UMIS), which allows the dentine to remain hydrated and thus is assumed to be closer to the in vivo conditions. Eight sound primary molar teeth were axially sectioned, embedded in resin and fine polished. Two linear arrays of indentations were done on coronal dentine, from the pulp wall to dentino-enamel junction (DEJ) parallel to the tubule direction under a force load of 25mN. The mean hardness and elastic modulus of the dentine nearest the pulp wall was 0.52+/-0.24 and 11.59+/-3.95GPa, respectively, which was significantly lower than those of dentine in the middle area, which was 0.85+/-0.19 and 17.06+/-3.09GPa, respectively, and the dentine nearest DEJ, which was 0.91+/-0.15 and 16.33+/-3.83GPa, respectively. There is a statistically significant linear correlation between the hardness and modulus of elasticity. The hardness and modulus of elasticity of dentine decreases with decreasing distance from the pulp. This is of importance to clinicians because an extension of cavity preparation towards the pulp may lead to less mechanical support for a restoration.
Publisher: Trans Tech Publications, Ltd.
Date: 03-2014
DOI: 10.4028/WWW.SCIENTIFIC.NET/KEM.606.121
Abstract: Hydrogels are very compliant materials suitable for tissue engineering in various areas of biological and clinical research. Appropriate and effective application of hydrogels for specific cellular regeneration often requires precise knowledge of their mechanical properties. The present work focuses on measurements of mechanical deformation and creep properties of polyacrylamide hydrogels using a novel indentation system. Four concentrations of polyacrylamide gel were tested under four different loading rates to study the mechanical response of the material to various loading rates. A spherical indenter with large radius was used in the experiments and all indentations were done with the s le completely immersed in water. The results show that higher acrylamide concentration in the gel leads to higher elastic modulus and decrease of creep. Similarly, faster loading rates lead to higher elastic modulus and larger creep during the hold period. The data were analyzed using both Hertzian fit to the loading part and Oliver-Pharr approach to the unloading part. The discrepancy between these two approaches and significant creep behavior are related to the viscoelasticity of the tested materials. This work contributes to understanding the results of instrumented indentation of extremely compliant materials with respect to their viscoelastic properties.
Publisher: Elsevier BV
Date: 09-2004
Publisher: Wiley
Date: 21-10-2011
Publisher: Elsevier BV
Date: 09-2004
Publisher: Informa UK Limited
Date: 06-1979
Publisher: Elsevier BV
Date: 03-2004
Publisher: Hindawi Limited
Date: 2013
DOI: 10.1155/2013/351279
Abstract: Purpose . This in vitro study investigates how unilateral and bilateral occlusal loads are transferred to an implant assisted removable partial denture (IARPD). Materials and Methods . A duplicate model of a Kennedy class I edentulous mandibular arch was made and then a conventional removable partial denture (RPD) fabricated. Two Straumann implants were placed in the second molar region, and the prosthesis was modified to accommodate implant retained ball attachments. Strain gages were incorporated into the fitting surface of both the framework and acrylic to measure microstrain ( μ Strain). The IARPD was loaded to 120Ns unilaterally and bilaterally in three different loading positions. Statistical analysis was carried out using SPSS version 18.0 (SPSS, Inc., Chicago, IL, USA) with an alpha level of 0.05 to compare the maximum μ Strain values of the different loading conditions. Results . During unilateral and bilateral loading the maximum μ Strain was predominantly observed in a buccal direction. As the load was moved anteriorly the μ Strain increased in the mesial area. Unilateral loading resulted in a twisting of the structure and generated a strain mismatch between the metal and acrylic surfaces. Conclusions . Unilateral loading created lateral and vertical displacement of the IARPD. The curvature of the dental arch resulted in a twisting action which intensified as the unilateral load was moved anteriorly.
Publisher: Wiley
Date: 10-10-2013
DOI: 10.1111/CLR.12272
Abstract: The objective of this study was to assess 1-year clinical success of one-piece zirconia implants compared with similar-design titanium implants, in the context of a novel protocol for implant distribution. Twenty-four edentulous participants were randomly allocated to one-piece titanium or zirconia implant group. Each participant received four implants in the maxilla (mid-palatal and three anterior crestal implants) and three implants in the mandible (mid-symphyseal and two bilateral distal implants). Conventional loading protocol was followed. Marginal bone remodeling and clinical success of implants were evaluated. The data were statistically analyzed, and risk predictors for implant failures were evaluated. There was no significant difference in the survival rate between the two groups. In the mandible, the survival rate of titanium implants was 95.8% vs. 90.9% for the zirconia implants. The corresponding values in the maxilla were 71.9% and 55%, respectively. Three implants in the zirconia group fractured. Statistically significant less marginal bone loss was observed around titanium implants (0.18 mm) compared with the zirconia group (0.42 mm). The prediction model revealed a higher risk for implant failures in the maxilla (P < 0.0001). The outcome of this study indicates caution before recommendation can be made for the use of single-piece zirconia implants for overdenture support. Their use should be limited to cases with proven allergy to titanium. This is mainly due to the increased bone loss and higher fracture rate observed for zirconia implants. Future biomaterial research should focus on producing surface characteristics on zirconia implants with outcomes similar to those established for the optimum osseointegration of titanium implants.
Publisher: Elsevier BV
Date: 09-2006
Publisher: Elsevier BV
Date: 06-2016
DOI: 10.1016/J.ARCHORALBIO.2016.02.012
Abstract: This paper aimed to precisely locate centres of resistance (CRe) of maxillary teeth and investigate optimal orthodontic force by identifying the effective zones of orthodontic tooth movement (OTM) from hydrostatic stress thresholds in the periodontal ligament (PDL). We applied distally-directed tipping and bodily forces ranging from 0.075 N to 3 N (7.5 g to 300 g) onto human maxillary teeth. The hydrostatic stress was quantified from nonlinear finite element analysis (FEA) and compared with normal capillary and systolic blood pressure for driving the tissue remodelling. Two biomechanical stimuli featuring localised and volume-averaged hydrostatic stresses were introduced to describe OTM. Locations of CRe were determined through iterative FEA simulation. Accurate locations of CRes of teeth and ranges of optimal orthodontic forces were obtained. By comparing with clinical results in literature, the volume average of hydrostatic stress in PDL was proved to describe the process of OTM more indicatively. The optimal orthodontic forces obtained from the in-silico modelling study echoed with the clinical results in vivo. A universal moment to force (M/F) ratio is not recommended due to the variation in patients and loading points. Accurate computational determination of CRe location can be applied in practice to facilitate orthodontic treatment. Global measurement of hydrostatic pressure in the PDL better characterised OTM, implying that OTM occurs only when the majority of PDL volume is critically stressed. The FEA results provide new insights into relevant orthodontic biomechanics and help establish optimal orthodontic force for a specific patient.
Publisher: BMJ
Date: 03-06-2013
DOI: 10.1136/JRAMC-2013-000075
Abstract: Indirect ballistic fractures occur when a projectile passes close to, but not contacting, the bone. The mechanism of how these fractures occur is not yet proven, but recently the acoustic shockwave has been excluded as a cause. The objective of this study is to determine whether the expanding temporary cavity, the collapse of this cavity or its oscillation causes these fractures. In addition, we describe the fracture morphology and biomechanical causes of this injury. 40 fresh deer femora were strain gauged and embedded in ballistic gelatin before being shot with four different projectiles with varying distances off the bone. Pressure recordings, chronographs and radar allowed assessment of local pressures and energy transfer. High-speed video allowed the temporal relationship between the temporary cavity and fracture formation to be analysed, while s le dissection allowed the fracture morphology to be described. The fractures produced were consistently wedge-shaped and caused by the expansion of the temporary cavity, flexing the bone beyond its yield point, causing tension failure on the cortex opposite the expanding temporary cavity and a compression wedge on the side of the cavity. Local pressure was not predictive of fracture formation but the energy transfer to the gelatin block was predictive. Indirect fractures are caused by the expansion of the temporary cavity and relate to the proximity of this cavity to the bone. Fractures occur from flexion of the bone and classically display wedge-shaped fracture patterns with the apex of the wedge pointing away from the expanding cavity.
Publisher: Springer Science and Business Media LLC
Date: 08-1973
DOI: 10.1007/BF00632767
Publisher: Trans Tech Publications, Ltd.
Date: 05-2014
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMM.553.384
Abstract: Implant-retained overdenture has been widely applied as a solution to edentulous ageing however, a major concern for the denture wearers is bone resorption induced by the prosthetic interaction with soft tissue and bone. Early studies have revealed that the bone resorption is associated with the disturbance to the mucosa blood flow. This study aimed to investigate the contact pressure induced by an implant-retained overdenture, compared to a conventional complete denture without implants, which implies the potential bone resorption for clinical investigation. A three-dimensional finite element model of a full jaw, including mandible bone, mucosa, and denture, was created through a reverse engineering method based on CBCT images, in which the hyperelastic behaviour of mucosa was determined by curve-fitting to the clinical measurement, for a more realistic response. It is found that the location of the bone loss differed between the implant retained and non-implant complete dentures. With the implants, the denture displaced more at posterior ends towards the mucosa bearing area, leading to higher contact pressure accounted for more severe local bone loss.
Publisher: Elsevier BV
Date: 05-2005
DOI: 10.1016/J.DENTAL.2004.07.010
Abstract: The purpose of this study was to investigate the influence of sandblasting, grinding, grinding orientation and polishing before and after heat treatment, on the flexural strength of a glass-infiltrated alumina/zirconia-reinforced dental ceramic (In-Ceram Zirconia). The uniaxial flexural strength was calculated on 160 bar-shaped specimens (20 x 4 x 1.2mm) ided equally into eight groups as follows: sandblasted sandblasted heated polished polished heated ground parallel to the tensile axis ground parallel heated ground perpendicular and ground perpendicular heated. Data were analyzed with multiple regression analysis, one-way ANOVA and Tukey's pairwise multiple comparisons and Weibull analysis. The treated and fractured surfaces were observed with SEM. The relative content of the monoclinic phase was quantified with an X-ray diffraction analysis. A thin layer of glass was present on the surface of the specimens after heat treatment and contributed to an improvement of the flexural strength. Surface treatment (not followed by heat treatment) generated phase transformation which, however, was not sufficient to avoid strength degradation caused by the flaws introduced with the surface treatments. Sandblasting caused the most marked strength degradation. Polishing alone increased the reliability, but did not improve the strength. The orientation of grinding in respect of the direction of the tensile stresses did not influence the ultimate tensile strength. The present study suggests that any surface treatment performed on In-Ceram Zirconia should always be followed by heat treatment to avoid strength degradation.
Publisher: Elsevier BV
Date: 06-2004
Publisher: Elsevier BV
Date: 06-2004
Publisher: Springer Science and Business Media LLC
Date: 1995
Abstract: The stress/strain behavior of bulk material is usually investigated in uniaxial tension or compression however, these methods are not generally available for very small volumes of material. Submicrometer indentation using a spherical indenter has the potential for filling this gap with, possibly, access to hardness and elastic modulus profiles, representative stress/strain curves, and the strain hardening index. The proposed techniques are based on principles well established in hardness testing using spherical indenters, but not previously applied to depth-sensing instruments capable of measurements on a submicrometer scale. These approaches are now adapted to the analysis of data obtained by stepwise indentation with partial unloading, a technique that facilitates separation of the elastic and plastic components of indentation at each step and is able to take account of the usually ignored phenomena of “piling up” and “sinking in”.
Publisher: Quintessence Publishing
Date: 05-2015
DOI: 10.11607/JOMI.3844
Abstract: This study aimed to investigate and compare the residual ridge resorption (RRR) induced by an implant-retained overdenture (IRO) and associative biomechanics and by a conventional complete denture (CD) without implants. Cone beam computed tomography was used to quantify RRR in a three-dimensional (3D) manner before and after 1 year of treatment with either IROs or CDs. Twenty patients were treated with IROs, and nine patients were treated with CDs in the mandible. Their maximum bite forces were recorded. The same sets of high-resolution scan images were used to create patient-specific 3D finite element analysis models. The hydrostatic stresses, contact surface deformation, and strain energy absorption in soft tissue mucosa were correlated with the changes in RRR for patients with and without implants. With the IROs, contact surface deformation on the mucosa was two times greater than with CDs (0.32 ± 0.23 mm vs 0.16 ± 0.06 mm) and was in agreement with the amount of RRR measured, which was also two times higher for the IRO than the CD (-3.8% ± 4.5% vs -1.9% ± 0.4%). Taking into account the differences in bite forces with and without implants, which again were twice as high with IROs, the hydrostatic stress within the mucosa was found to correlate well to the RRR map measured over the 1-year interval of treatment. IROs resulted in at least twice the RRR as CDs. This could be caused by the higher hydrostatic stress and less effective energy absorption capabilities of the mucosa underneath the IRO. While implants associated with the IRO provide stronger bite force, they could potentially concentrate hydrostatic stress and cause greater RRR compared to a conventional CD.
Publisher: Japanese Society for Dental Materials and Devices
Date: 2001
DOI: 10.4012/DMJ.20.227
Abstract: A nano-indentation test was applied to determine elastic modulus (E) and hardness (H) of dentin. Three spherical indenters with nominal radii of 20, 5 and 1 microns were used and load artial-unload cycles were repeated. Each cycle provided E and contact pressure or Meyer's hardness. The plot of contact pressure versus penetration depth was converted into a normalized indentation stress-strain relationship, which was used to select the optimum maximum indentation force for each indenter. The results were compared with those determined by the conventional triangular pyramidal (Berkovich) indenter technique. The comparable E value, irrespective of radius, was 19.5-20.9 GPa and the 1 micron indenter was able to provide E values of peritubular (28.0 GPa) and intertubular dentin (14.9 GPa). The H values generated with the Berkovich indentation technique were comparable to those determined by the spherical indenter technique at indentation strains of 0.9 and 0.5 for the 1 and 5 microns indenters.
Publisher: Elsevier BV
Date: 03-2014
DOI: 10.1016/J.DENTAL.2013.11.011
Abstract: The aim of this study was to investigate the influence of increasing veneering porcelain thickness in clinically representative zirconia molar crowns on the residual stresses under fast and slow cooling protocols. Six veneered zirconia copings (Procera, Nobel Biocare AB, Gothenburg, Sweden) based on a mandibular molar form, were ided into 3 groups with flattened cusp heights that were 1mm, 2mm, or 3mm. Half the s les were fast cooled during final glazing the other half were slow cooled. Vickers indentation technique was used to determine surface residual stresses. Normality distribution within each s le was done using Kolmogorov-Smirnov & Shapiro-Wilk tests, and one-way ANOVA tests used to test for significance between various cusp heights within each group. Independent t-tests used to evaluate significance between each cusp height group with regards to cooling. Compressive stresses were recorded with fast cooling, while tensile stresses with slow cooling. The highest residual compressive stresses were recorded on the fast cooled 1mm cusps which was significantly higher than the 2 and 3mm fast cooled crowns (P<0.05). There was a significant linear trend for residual stress to decrease as veneering porcelain thickness increased in the fast cooled group (P<0.05). No significant differences were found between the various cusp heights during slow cooling (P≥0.05). Cooling rate and geometric influences in a crown anatomy have substantially different effects on residual stress profiles with increasing veneering porcelain thickness compared to the basic flat plate model.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4NR03180F
Abstract: A novel mechanism of highly mineralized bone durability almost independent of viscoelastic behaviour along with a series of nanoindentation experiments is reported.
Publisher: AIP Publishing
Date: 08-01-2001
DOI: 10.1063/1.1335552
Abstract: The deformation behavior of wurtzite GaN films modified by ion bombardment is studied by nanoindentation with a spherical indenter. Results show that implantation disorder significantly changes the mechanical properties of GaN. In particular, GaN amorphized by ion bombardment exhibits plastic deformation even for very low loads with dramatically reduced values of hardness and Young’s modulus compared to the values of as-grown GaN. Implantation-produced defects in crystalline GaN suppress the plastic component of deformation and significantly change the values of hardness and Young’s modulus. In addition, implantation disorder in crystalline GaN suppresses both “pop-in” events during loading and the appearance of slip traces on the s le surface as a result of indentation. This strongly suggests that slip nucleation (rather than a phase transformation) is the physical mechanism responsible for the pop-in events observed during loading of as-grown crystalline GaN.
Publisher: SPIE-Intl Soc Optical Eng
Date: 2009
DOI: 10.1117/1.3253396
Abstract: Laser ultrasonic nondestructive evaluation (NDE) methods have been proposed to replace conventional in vivo dental clinical diagnosis tools that are either destructive or incapable of quantifying the elasticity of human dental enamel. In this work, a laser NDE system that can perform remote measurements on s les of small dimensions is presented. A focused laser line source is used to generate broadband surface acoustic wave impulses that are detected with a simplified optical fiber interferometer. The measured surface wave velocity dispersion spectrum is in turn used to characterize the elasticity of the specimen. The NDE system and the analysis technique are validated with measurements of different metal structures and then applied to evaluate human dental enamel. Artificial lesions are prepared on the s les to simulate different states of enamel elasticity. Measurement results for both sound and lesioned regions, as well as lesions of different severity, are clearly distinguishable from each other and fit well with physical expectations and theoretical value. This is the first time, to the best of our knowledge, that a laser-based surface wave velocity dispersion technique is successfully applied on human dental enamel, demonstrating the potential for noncontact, nondestructive in vivo detection of the development of carious lesions.
Publisher: Elsevier BV
Date: 02-2017
DOI: 10.1016/J.JOEN.2017.10.009
Abstract: Spontaneously catastrophic fracture of intact unrestored molar teeth is not common. Nevertheless, cracks do occur that progress apically, resulting in the complete splitting of the tooth and root. This report describes a catastrophic fracture that occurred in an unrestored mandibular second molar resulting in a previously unreported combination of a longitudinal and horizontal root fracture, appearing radiographically as a single horizontal root fracture. Tooth fragments were examined clinically, stereoscopically, and by scanning electron microscopy. Fractographic analysis was used to investigate the dynamics involved in fracture initiation, structural resistances encountered during progression of the fracture, and reasons for direction changes culminating in the unusual radiographic appearance. The uniqueness of this report is that it describes fractographic evidence of factors contributing to the initiation and progression of an in vivo crack. It shows fracture markings that are evidence of the energy dissipation mechanisms. The topographic location of these markings confirmed that cracks occur in vivo in stages with different rates of progression. This analysis helps to explain why split teeth are uncommon and highlights some of the multitude of factors that have to coincide for a tooth to catastrophically fracture. The report describes the mechanism of fracture and should stimulate clinicians and researchers to investigate cracking of teeth by undertaking fractographic analysis of extracted cracked teeth.
Publisher: Elsevier BV
Date: 2001
DOI: 10.1016/S8756-3282(00)00414-2
Abstract: Osteoporotic fractures commonly occur in the elderly. Although current therapies are aimed at the prevention and treatment of osteoporotic fractures, studies examing the fracture healing process in osteoporotic bone are limited. We produced an osteoporotic rat model by ovariectomy (ovx) and maintained a low calcium diet (LCD) in order to evaluate the influence of osteoporosis on fracture healing. Callus formation and strength was monitored over a 3 week period by histological and biomechanical assessment. Data collected simultaneously on a group of rats undergoing sham surgery (sx) were used for comparison. A 40% reduction in fracture callus cross-sectional area and a 23% reduction in bone mineral density in the healing femur of the ovx rats was observed on day 21 following fracture as compared with the sx group (p < 0.01). Biomechanical data from the healing femur of the ovx rats revealed a fivefold decrease in the energy required to break the fracture callus, a threefold decrease in peak failure load, a twofold decrease in stiffness and a threefold decrease in stress as compared with the sx group (p < 0.01, respectively). Histomorphological analysis revealed a delay in fracture callus healing with poor development of mature bone in the ovx rats. This study provides physical evidence of altered fracture healing in osteoporotic bone, which may have important implications in evaluating the effects of new treatments for osteoporosis on fracture healing.
Publisher: Wiley
Date: 17-03-2011
DOI: 10.1111/J.1708-8208.2010.00334.X
Abstract: Computer numeric controlled (CNC) milling was proven to be predictable method to fabricate accurately fitting implant titanium frameworks. However, no data are available regarding the fit of CNC-milled implant zirconia frameworks. To compare the precision of fit of implant frameworks milled from titanium and zirconia and relate it to peri-implant strain development after framework fixation. A partially edentulous epoxy resin models received two Branemark implants in the areas of the lower left second premolar and second molar. From this model, 10 identical frameworks were fabricated by mean of CNC milling. Half of them were made from titanium and the other half from zirconia. Strain gauges were mounted close to the implants to qualitatively and quantitatively assess strain development as a result of framework fitting. In addition, the fit of the framework implant interface was measured using an optical microscope, when only one screw was tightened (passive fit) and when all screws were tightened (vertical fit). The data was statistically analyzed using the Mann-Whitney test. All frameworks produced measurable amounts of peri-implant strain. The zirconia frameworks produced significantly less strain than titanium. Combining the qualitative and quantitative information indicates that the implants were under vertical displacement rather than horizontal. The vertical fit was similar for zirconia (3.7 µm) and titanium (3.6 µm) frameworks however, the zirconia frameworks exhibited a significantly finer passive fit (5.5 µm) than titanium frameworks (13.6 µm). CNC milling produced zirconia and titanium frameworks with high accuracy. The difference between the two materials in terms of fit is expected to be of minimal clinical significance. The strain developed around the implants was more related to the framework fit rather than framework material.
Publisher: Wiley
Date: 04-2013
DOI: 10.1111/JOPR.12031
Abstract: This study analyzes the effects of loading a Kennedy class I implant-assisted removable partial denture (IARPD) using finite element analysis (FEA). Standard RPDs are not originally designed to accommodate a posterior implant load point. The null hypothesis is that the introduction of posteriorly placed implants into an RPD has no effect on the load distribution. A Faro Arm scan was used to extract the geometrical data of a human partially edentulous mandible. A standard plus regular neck (4.8 × 12 mm) Straumann® implant and titanium matrix, tooth roots, and periodontal ligaments were modeled using a combination of reverse engineering in Rapidform XOR2 and solid modeling in Solidworks 2008 FEA program. The model incorporated an RPD and was loaded with a bilateral force of 120 N. ANSYS Workbench 11.0 was used to analyze deformation in the IARPD and elastic strain in the metal framework. FEA identified that the metal framework developed high strain patterns on the major and minor connectors, and the acrylic was subjected to deformation, which could lead to acrylic fractures. The ideal position of the neutral axis was calculated to be 0.75 mm above the ridge. A potentially destructive mismatch of strain distribution was identified between the acrylic and metal framework, which could be a factor in the failure of the acrylic. The metal framework showed high strain patterns on the major and minor connectors around the teeth, while the implant components transferred the load directly to the acrylic.
Publisher: Elsevier BV
Date: 1994
Publisher: Trans Tech Publications, Ltd.
Date: 03-2014
DOI: 10.4028/WWW.SCIENTIFIC.NET/KEM.606.117
Abstract: The corneoscleral rim of the eye represents a region with unique anatomical properties due to its location between the cornea and sclera / conjunctiva. It further has unique functional properties due to the location of adult corneal epithelial stem cells in the rim structure (limbus) itself. These stem cells are essential for the regeneration of the corneal epithelium and for preventing the conjunctival epithelium from growing onto the corneal surface, which could result in blindness. Survival and self-renewal properties of stem cells are known to depend on specific biological and biomechanical properties of its niche environment. We therefore aimed to measure the local mechanical properties of the human corneoscleral rim using a novel nanoindentation device (Bioindenter CSM Instruments, Neuchâtel, Switzerland) developed for soft tissues evaluation. Nanoindentation was performed using a spherical indenter of 0,5mm radius, a maximal load ranging between 20 μN to 30 μN and a penetration depth of several μm to 60μm. The hold period at maximum load was 180 seconds. Youngs modulus ( E ) was calculated using a Hertzian fit to the loading data. E of the central cornea was in the range of 19 kPa, while in the scleral region we found 17 kPa and the limbal rim region 10 kPa. Considerable creep relaxation occurred during the hold period at maximum load, which scaled with the elastic modulus of the different structures. These results reveal biomechanical properties of the corneoscleral rim with distinct mechanical properties for the three anatomical regions.
Publisher: Springer Science and Business Media LLC
Date: 2000
Abstract: Measurement of the elastic modulus (E) of investment materials has been difficult because of their low strength. However, these values are essential for engineering simulation and there are many methods available to assess the elasticity of materials. The present study compared two different methods with one of the methods being non-destructive in nature and can be used for specimens prepared for other tests. Two different types of investment materials were selected, gypsum-and phosphate-bonded. Method 1 is a traditional three-point bending test. Twelve rectangular bars with dimension of (70 x 9 x 3 mm) were prepared and placed on supports 56.8 mm apart. The test was conducted at a cross-head speed of 1 mm/min by use of a universal testing machine. The load applied to the test specimen and the corresponding deflection were measured until the specimen fractured. The E value was calculated from a linear part of the stress-strain plot. Method 2 is an ultra micro-indentation system to determine near surface properties of materials with nanometer resolution. The measurement procedure was programmed such that the specimens were indented with an initial contact force of 5 mN then followed by a maximum force of 500 mN. Measurement consisted of 10 indentations conducted with a spherical stainless steel indenter (R = 250 microm) that were equally spaced (500 microm). The E value rose asymptotically with depth of penetration and would approach the three-point bending test value at approximately four time's maximum contact depth for both materials. Both methods are practical ways of measuring the E of investment materials.
Publisher: Elsevier BV
Date: 09-2007
DOI: 10.1016/J.JDENT.2007.06.001
Abstract: The aim of this study was to characterise the mineral density (MD) of natural enamel white spot lesions (WSLs) using X-ray micro-tomography calibrated with different density hydroxyapatite phantoms. Seven natural WSLs from four extracted non-carious premolar teeth were scanned at a voxel size of 7.6 microm using a desktop X-ray micro-tomography system. Five hydroxyapatite phantoms (sintered pellets of hydroxyapatite powder) with densities ranging from 1.52 to 3.14 g/cm(3) were used as calibration standards for each scan. Three-dimensional image reconstruction enabled MD gradients throughout the lesion to be quantified using an MD calibration equation derived from hydroxyapatite phantoms. Background noise generated during the measurement of MD was reduced using a Gaussian filter. Gaussian filter reduced the signal-to-noise ratio (standard deviation) significantly while the basic MD information (average value) remained intact. The mineral gradients through the WSLs examined were compared and are discussed in terms of existing literature. The MD of sound enamel, apparent intact surface layer of WSL, and lowest level of WSL was found to be 2.65-2.89 g/cm(3), 2.23-2.58 g/cm(3) and 1.48-2.03 g/cm(3), respectively. Our MD results are comparable with other studies. X-ray micro-tomography is a sensitive in vitro technique capable of characterising and quantifying MD of small non-cavitated WSLs. This method has a promising potential for future carious and quantitative remineralisation studies.
Publisher: S. Karger AG
Date: 2010
DOI: 10.1159/000286214
Abstract: The aim of this paper was to characterise the mechanical properties (MPs) and microstructural features of natural enamel white spot lesions (WSLs) using nano-indentation. Five natural WSLs from 4 extracted sound premolar teeth were cross-sectioned. Elastic modulus and hardness were measured systematically across the WSLs at intervals of 25 and 50 µm. The WSLs showed a large reduction in MPs compared to sound counterpart: elastic modulus was up to 83% lower (77.0 ± 2.2 to 13.4 ± 2.1 GPa) and hardness up to 91% lower (3.39 ± 0.41 to 0.29 ± 0.07 GPa). The intact surface layer above WSLs had less than 34% reduction in MPs. Detailed MP measurements were mapped as two-dimensional contour plots. Typically, WSLs displayed steep MP gradients at the lesion boundary and more uniform MPs with isolated variations in the lesion body. Despite the large reduction in MPs, the microstructure of WSLs remained intact. We postulate that loss of mineral and change of the hierarchical microstructure at the crystallite level contributed to the overall MPs of WSLs.
Publisher: Oxford University Press (OUP)
Date: 08-06-2006
DOI: 10.1093/EJO/CJL007
Abstract: This clinical trial evaluated, over a 12-month period, the performance of brackets bonded to teeth etched and primed with Transbond Plus Self-Etching Primer (SEP) when compared with a conventional separate two-step etch and primer system. Thirty-nine randomly selected patients requiring fixed appliance therapy were entered into the study. Random allocation of each etching system, along with a 'split-mouth cross-quadrant' design was used. A total of 661 brackets were placed by two operators. The failure and survival rates of the brackets were determined for age and gender of the patients, each etching system, operator, mode of failure, tooth position in the dental arch, and number of manipulations prior to curing the adhesive. Statistical analysis showed that SEP had a significantly higher bond failure rate (11.2 per cent) than the conventional etch and primer system (3.9 per cent) at the P = 0.001 level. Cox's proportional hazards regression showed the conventional etch and primer system to have a 60 per cent reduced chance of bracket failure over a 12-month observation period, while males had a 2.4 times increased risk compared with females. The predominant mode of failure was at the composite enamel interface for the SEP, while for the conventional etch and primer system, it was within the composite adhesive. No statistically significant differences were found for the failure rate with respect to the age of the patient, operator, tooth location, or the number of manipulations of the bracket. This in vivo study showed that brackets bonded using SEP had an increased clinical bond failure rate compared with the conventional, separate, etch and prime system.
Publisher: Trans Tech Publications, Ltd.
Date: 08-2009
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.79-82.2167
Abstract: This paper aims at providing a preliminary understanding in biomechanics with respect to the effect of FPC dental implants on bone remodelling. 2D multi-scale finite element models are created for a typical dental implantation setting. Under a certain mastication force ( N), a global response from a macro-scale model (without considering coated surface morphology details) is first obtained and then it is transferred to the micro-scale models (with coated surface morphology details and various particle sizes) for micro-scale analysis. A strain energy density (SED) obtained from 2D micro-scale Finite Element Analysis (FEA) is used as a mechanical stimulus to determine the bone remodeling in term of the change in apparent bone densities for cancellous and cortical bones. The change in bone densities is examined as a result of bone remodelling activities over a period of 48 months.
Publisher: Wiley
Date: 08-1989
Publisher: Wiley
Date: 11-1991
Publisher: Quintessence Publishing
Date: 2013
DOI: 10.11607/JOMI.2303
Abstract: To evaluate the biomechanics of a novel implant placement distribution and compare it with that of conventional maxillary overdenture support using three-dimensional finite element analysis (FEA). The application of zirconia implants in the context of this novel design was also evaluated. Detailed FEA models were created to analyze the loading responses of two different distributions of implants to support maxillary overdentures. The two implant distributions were as follows: the conventional design (D1) included four unsplinted implants in the premolar regions, whereas the novel design (D2) included one midpalatal implant, bilateral canine remolar implants, and one anterior off-center crestal implant. Anatomical models were created with computed tomographic data and static loads were applied axially and obliquely. Von Mises stresses and equivalent strains generated in peri-implant bone and first principal stresses in the implants were calculated, including any denture displacement. Comparable stress and strain values were seen in the peri-implant bone for both designs. A significant decrease in the first principal stresses of D2 implants was observed with oblique loads. The maximum equivalent strain produced in the peri-implant region was mostly within the range for bone augmentation. D2 displayed lower maximum displacement values than D1. Maximum tensile stresses in the zirconia implants for either design were well below their fracture strength. A novel four-implant distribution involving midpalatal and crestal implants may be an alternative to the conventional design used for maxillary overdentures. This is particularly relevant when anatomical considerations prevent the placement of four anterior crestal implants. Zirconia implants may also be a valid option for a selected group of patients or for those requesting metal-free restorations. Prospective clinical studies are required to confirm these in vitro results.
Publisher: Elsevier BV
Date: 06-2012
DOI: 10.1016/J.DENTAL.2012.02.008
Abstract: To verify the hypothesis that crack analysis and a mechanical test would rank a series of composites in a similar order with respect to polymerization stress. Also, both tests would show similar relationships between stress and composite elastic modulus and/or shrinkage. Soda-lime glass discs (2-mm thick) with a central perforation (3.5-mm diameter) received four Vickers indentations 500 μm from the cavity margin. The indent cracks were measured (500×) prior and 10 min after the cavity was restored with one of six materials (Kalore/KL, Gradia/GR, Ice/IC, Wave/WV, Majesty Flow/MF, and Majesty Posterior/MP). Stresses at the indent site were calculated based on glass fracture toughness and increase in crack length. Stress at the bonded interface was calculated using the equation for an internally pressurized cylinder. The mechanical test used a universal testing machine and glass rods (5-mm diameter) as substrate. An extensometer monitored specimen height (2mm). Nominal stress was calculated iding the maximum shrinkage force by the specimen cross-sectional area. Composite elastic modulus was determined by nanoindentation and post-gel shrinkage was measured using strain gages. Data were subjected to one-way ANOVA/Tukey or Kruskal-Wallis/Mann-Whitney tests (alpha: 5%). Both tests grouped the composites in three statistical subsets, with small differences in overlapping between the intermediate subset (MF, WV) and the highest (MP, IC) or the lowest stress materials (KL, GR). Higher stresses were developed by composites with high modulus and/or high shrinkage. Crack analysis demonstrated to be as effective as the mechanical test to rank composites regarding polymerization stress.
Publisher: Elsevier BV
Date: 11-2008
DOI: 10.1016/J.JDENT.2008.07.012
Abstract: To study the relation between the mechanical properties of hypomineralised enamel, and its laser fluorescence (LF). Five extracted teeth with molar-incisor hypomineralisation (MIH) were sectioned longitudinally through the defects and polished to prepare the hypomineralised enamel for testing. Hardness (H) and elastic modulus (E) of enamel were measured using nanoindentation. Measurement recording started from the cervicoenamel junction and proceeded occlusally in increments of 200 microm. Laser fluorescence readings were taken along the same line and at the same sites using a DIAGNOdent pen. H, E, and LF readings from cervical enamel were within the expected range for normal sound enamel. After log transformation of the H and E measurements to allow for linear correlation analysis, there was a significant and moderately strong inverse correlation between LF and H or E s les (r (between specimens)=0.59, r (between specimens)=0.39, respectively p<0.001). This study shows that, in the absence of dental caries, increased DIAGNOdent readings can indicate enamel hypomineralisation. While the increased LF readings in carious enamel are thought to be related to the presence of caries bacterial metabolites, the increased readings in hypomineralised enamel may be related to proteins in the hypomineralised enamel and/or light scattering by the inhomogeneous enamel.
Publisher: Springer Science and Business Media LLC
Date: 04-2007
Abstract: Poly(methyl methacrylate) was contacted by a Berkovich indenter at a range of constant loading strain rates. This particular loading scheme was used to maintain the strain-rate-dependent elastic modulus and indentation hardness of the creeping solid constant throughout loading. A loading curve analysis method identical to that of Malzbender and de With but based on the elastic-perfectly plastic contact model of Hochstetter et al. [ Tribol. Int. 36, 973–985, 2003] was used to process the load-displacement curves. Using the analysis method together with the strain-rate-dependent elastic modulus of the creeping solid known a priori, the strain-rate-dependent hardness could then be predicted. The predicted hardness versus strain-rate relationship was compared with that evaluated from the observed topographic images of the residual impressions due to heavier indentations at three constant loading strain rates. Based on this comparison, the elastic-perfectly plastic contact model was shown to be applicable to the creeping solid only when deformation takes place at a quasi-static strain rate.
Publisher: Wiley
Date: 04-06-2023
Abstract: Providing optimal support for carers of people with advanced cancer is critical to facilitating discharge home from hospital. Carer Support Needs Assessment Tool–Intervention (CSNAT‐I) has shown promise in supporting carers' needs in this context. This study aimed to explore patient and carers experiences with and views on the acceptability of the CSNAT‐I delivered by occupational therapists in an acute oncology setting. People with advanced cancer and their carers who had previously received the CSNAT‐I as part of usual care while admitted to an Australian specialist cancer centre or acute hospital were invited to participate in interviews exploring their perceptions of the intervention. Data were analysed thematically. Two patients and 10 carers participated in semi‐structured interviews. Three themes were constructed from the data: Carers viewed the CSNAT‐I as comprehensive process that (1) ‘covered everything’ related to discharge planning (2) generated an ‘increased awareness of needs’ for themselves, patients, and clinicians and (3) triggered an emotional response of feeling ‘wrapped up in care’ that was maintained as they moved from hospital to home. This study has demonstrated that the CSNAT‐I was highly acceptable to carers as part of existing discharge processes supporting them through the transition from hospital to home and can be delivered by occupational therapists and other clinicians with a natural synergy to discharge planning. These findings will inform further development and testing of the delivery model of the CSNAT‐I in future trials.
Publisher: Springer Science and Business Media LLC
Date: 05-11-1999
Publisher: No publisher found
Date: 2008
DOI: 10.1007/S10439-007-9424-5
Abstract: The force imparted by removable thermoplastic appliances (RTA) onto teeth has not been investigated in the past. This investigation was designed to explore a novel methodology to measure the magnitude and identify the pattern of this force. Eight patients with moderate malocclusion were selected. In each patient, the palatally mal-positioned upper first premolar was corrected by wearing a series of four ClearSmile RTA over a duration of 8 weeks. When constructing RTA, the ClearSmile Company was advised that the amount of movement to be programmed into each appliance was 0.5 mm. The Pressurex film was used to measure the pressure generated by ClearSmile RTA against the palatal surface of the upper first premolar for buccal tipping movement. Three measurements were conducted respectively upon the issue and retrieval of each appliance (after 2 weeks of wear), resulting in 24 pressure measurements for each patient. Digital imaging and spectrophotometry analysis were employed to quantify the stain intensity mounted by the pressure on the films. The irrelevant forces were subtracted out to allow an assessment of the force purely acting to buccally repositioning the tooth. The results revealed that (1) the mean force magnitude over 2 weeks of RTA wear was 1.12 N (SE = 0.72 N) (2) the higher force magnitude of 5.12 N (SE = 0.80 N) seen at the issue of the appliance declined drastically to -2.67 N at the time of retrieval. These findings suggest that ClearSmile RTA exerts a high level of force against the tooth to be moved at the initial stage followed by a rapid force diminish.
Publisher: Elsevier BV
Date: 2014
DOI: 10.1016/J.JSB.2013.11.006
Abstract: Dolphins show increased tooth number and simplified tooth shape compared to most mammals, together with a simpler ultrastructural organization and less demanding biomechanical function. However, it is unknown if these factors are also reflected in the chemical composition of their teeth. Here, the bulk chemical composition and elemental distribution in enamel and dentine of extant dolphins were characterized and interpreted using X-ray and spectroscopy techniques. Teeth of 10 species of Delphinida were analyzed by WDX, EDX and Raman spectroscopy. For most of the species s led, the mineral content was higher in enamel than in dentine, increasing from inner towards outer enamel. The transition from dentine to enamel was marked by an increase in concentration of the major components Ca and P, but also in Na and Cl. Mg decreased from dentine to enamel. Concentrations of Sr and F were often low and below detection limits, but F peaked at the outer enamel region for some species. Raman spectroscopy analyzes showed characteristics similar to carbonated hydroxyapatite, with the strongest peak for the phosphate PO4(3-) stretching mode at 960-961cm(-1). Dentine s les revealed a higher ersity of peaks representative of organic components and proteins than enamel. The similar distribution pattern and small variation in average concentration of major and minor elements in dentine and enamel of dolphins suggest that they are subject to strong physiological control. A clear trend of the elemental variations for all dolphin species s led suggests that the general pattern of tooth chemistry is conserved among the Mammalia.
Publisher: Wiley
Date: 08-1991
Publisher: Springer Science and Business Media LLC
Date: 14-05-2008
DOI: 10.1007/S12024-008-9042-Z
Abstract: Despite a long history of gross and microscopic descriptions of blunt and sharp force injury to the dermal tissues, few have addressed the mechanisms underlying such trauma. The need to develop an understanding of how non-ballistic injury occurs calls for an ability to biomechanically model the process. We recently introduced a basic skin and subcutaneous model, which we used to investigate wounding from a spherical object. Here we employ the same model to examine wounding caused by a sharp wedge shaped object and a blunt rectangular object. Macroscopic examination and SEM views of the surface and cross sections of blunt and sharp force tears show that while in the former there is a clean cut through the skin into the underlying sponge, in the latter there is a tissue plug confined to the skin that is smaller than the impacting rectangle. Fracture initiation in the subdermal tissue occurs at the angles of the impacting object. In sharp force trauma, there is localized breaching of the skin layer coupled with the wedging action of the impacting object. Because the subdermal tissue, in this case the underlying hydrated foam, is attached to the base of the skin, it will contribute to further tearing of the foam beneath the line of contact.
Publisher: Elsevier BV
Date: 1998
Publisher: Elsevier BV
Date: 03-2007
DOI: 10.1016/J.BIOMATERIALS.2006.10.035
Abstract: One of the most frequent causes of degradation and failure of quasi-brittle biomaterials is fracture. Mechanical breakdown, even when not catastrophic, is of particular importance in the area of biomaterials, as there are many clinical situations where it opens the path for biologically mediated failures. Over the past few decades the materials/biomaterials community has developed a number of numerical models, but only with limited incorporation of brittle failure phenomena. This article investigates the ability of a non-linear elastic fracture mechanics (NLEFM) model to reliably predict failure of biomaterials with a specific focus on the clinical settings of restorative dentistry. The approach enables one to predict fracture initiation and propagation in a complex biomechanical status based on the intrinsic material properties of the components. In this paper, we consider five ex les illustrating the versatility of the present approach, which range from the failure of natural biomaterials, namely dentine and enamel, to a restored tooth, a three unit all ceramic bridge structure and contact-induced damage in the restorative layered materials systems. It is anticipated that this approach will have ramifications not only to model fracture events but also for the design and optimisation of the mechanical properties of biomaterials for specific clinically determined requirements.
Publisher: Elsevier BV
Date: 2007
DOI: 10.1016/J.JDENT.2006.04.003
Abstract: The aim of this paper was to investigate the influence of lesion shape and depth as well as the direction of occlusal loading on the mechanical response of cervical GIC restorations. A finite element model of a lower first premolar was created. Both wedged and rounded lesions were then modelled with incremental depth after which the tooth was loaded at different angles. First principal stress (tension) was employed as an indicator of material failure, by contrasting our calculated stresses with the ultimate tensile strength of the GIC and known values of bond strength between material and tooth substrate. Obliquely loaded teeth exhibited significantly higher tensile stress in the cervical region of the restoration. For forces inclined at angles of 30 degrees and higher to the vertical tooth axis, the tensile stresses in the cervical margin of the restoration exceeded the ultimate material and bond strength. In contrast, lesion shape and depth have only a minor influence on tensile stress development. Lesion depth and shape are not of primary concern from a mechanical perspective for a restorative treatment decision. By contrast, occlusal diagnosis and subsequent re-adjustments of tooth contacts do form a critical part of the treatment of non-carious cervical lesions (NCCLs).
Publisher: Elsevier BV
Date: 02-2004
DOI: 10.1016/J.ARCHORALBIO.2003.08.006
Abstract: Backscattered electron-scanning electron microscope (BSE-SEM) imaging has been recommended as a reliable tool to quantify the mineralisation state of calcified tissues and is commonly used in bone studies. The aim of this study is to investigate the use of BSE imaging to quantitatively analyse the mineral content of sound and carious dentine. Eight primary molars with untreated carious dentine were embedded in resin, axially sectioned and fine polished for this study. The BSE images were from a solid-state detector in an SEM operating at 1.5Torr gas pressure. BSE images of a number of different elements and compounds with atomic number ranged from 4 to 26 were analysed prior to the test to calibrate the experimental conditions and an enamel-carbon block. The mineral analysis was based on the change in BSE intensity (measured in graylevels). The results showed that variation in graylevels accurately represented difference in the atomic number and BSE coefficient of the test materials. The mineral content of sound primary dentine in the most regions was 59.3+/-5.5 wt.%, but it decreased gradually to be just 41.82+/-6.74 wt.% adjacent to the pulp. The carious dentine showed a marked reduction in mineral content which proceeded progressively toward the cavity floor, in which the minimum value of less than 10 wt.% was normally found in the outer layer of the lesion. The results show that BSE imaging is a simple and reliable technique that can be used to quantify the mineral content of sound and carious dentine. More importantly the variable pressure SEM offers an approach to minimize the impact of dehydration on carious dentine specimens.
Publisher: SAGE Publications
Date: 21-09-2011
Abstract: Accurate assessment of mineral density (MD) provides information critical to the understanding of mineralization processes of calcified tissues, including bones and teeth. High-resolution three-dimensional assessment of the MD of teeth has been demonstrated by relatively inaccessible synchrotron radiation microcomputed tomography (SRµCT). While conventional desktop µCT (CµCT) technology is widely available, polychromatic source and cone-shaped beam geometry confound MD assessment. Recently, considerable attention has been given to optimizing quantitative data from CµCT systems with polychromatic x-ray sources. In this review, we focus on the approaches that minimize inaccuracies arising from beam hardening, in particular, beam filtration during the scan, beam-hardening correction during reconstruction, and mineral density calibration. Filtration along with lowest possible source voltage results in a narrow and near-single-peak spectrum, favoring high contrast and minimal beam-hardening artifacts. More effective beam monochromatization approaches are described. We also examine the significance of beam-hardening correction in determining the accuracy of mineral density estimation. In addition, standards for the calibration of reconstructed grey-scale attenuation values against MD, including K 2 PHO 4 liquid phantom, and polymer-hydroxyapatite (HA) and solid hydroxyapatite (HA) phantoms, are discussed.
Publisher: Elsevier BV
Date: 02-2004
DOI: 10.1016/J.JDENT.2003.08.006
Abstract: During laboratory fabrication procedures and/or clinical adjustments, pressable materials: IPS Empress and Empress 2, may be ground, polished or sandblasted. These treatments may affect their strength by introducing microscopic flaws and defects. This study investigates the effect of these procedures on the mean flexural strength of these materials. One hundred and forty disc specimens (14mmx1 mm) of IPS Empress and Empress 2 were prepared, and ided into seven groups of 20 specimens for each material. Groups were untreated, polished, polished and glazed, ground, ground and glazed, sandblasted, sandblasted and glazed. Surface roughness, mean biaxial flexural strength and Weibull modulus were appraised, and a scanning electron microscope was used to describe surface features. Statistical significance among groups of population was analysed using one-way Anova and Tukey's multiple comparison tests. Untreated and sandblasted groups showed significantly the highest roughness values, and polished the lowest for each material (p<0.05). Ground groups showed significantly lower roughness values than the sandblasted groups, and significantly higher roughness than the polished groups for each material (p<0.05). Polished groups for each material demonstrated significantly the highest mean flexural strength values (p 0.05). Heat treatment had no effect on roughness or strength values of all treated groups of both materials. The Weibull modulus values for both materials varied with different treatments. They showed higher values for polished and untreated groups, and lower values for ground and sandblasted groups. Surface roughness may not be the only feature that determines strength. Other issues such as porosity, microstructural residual stresses, surface and bulk defects may also be pertinent.
Publisher: Elsevier BV
Date: 06-2009
DOI: 10.1016/J.ACTBIO.2008.12.016
Abstract: The central argument of this study is that residual stresses developed during the preparation of all-ceramic crowns and fixed partial dentures coupled with contact-induced cracking are the origin of the excessive chipping observed in clinical applications. The aim of this paper is to provide a simple basic analysis of the causes of residual stress development in ceramics and identify the key thermo-mechanical parameters responsible for these stresses and the resultant contact-induced failure. For simplicity, a bilayer planar geometry is considered. The key outcomes are the critical role of thermo-elastic properties and the thickness of the structures. The approach is then used to evaluate the propensity for unstable cracking of a range of crown structures, including substructures of a range of ceramics, and to show that two specific combinations are most prone to this behaviour, namely porcelain fused to glass ceramics and zirconia substrates. In addition, a simple approach for the minimization of the likelihood for such behaviour and chipping is proposed.
Publisher: Elsevier BV
Date: 08-2011
Publisher: IOP Publishing
Date: 1991
Publisher: Wiley
Date: 03-11-2009
DOI: 10.1002/JBM.A.32223
Abstract: In this study, the indentation creep behavior of human enamel was investigated with a nanoindentation system and a Berkovich indenter at a force of 250 mN with one-step loading and unloading method. A constant hold period of 900 s was incorporated into each test at the maximum load as well at 5 mN minimum load during unloading. The indentation creep at the maximum load and creep recovery at the minimum load was described with a double exponential function and compared with other classic viscoelastic models (Debye/Maxwell and Kohlrausch-Williams-Watts). Indentation creep rate sensitivity, m, of human enamel was measured for the first time with a value of approximately 0.012. Enamel displayed both viscoelastic and viscoplastic behavior similar to that of bone. These results indicate that, associated with entrapment of particulates between teeth under functional loading and sliding wear conditions, the enamel may inelastically deform but recover upon its release. This behavior may be important in explaining the excellent wear resistance, antifatigue, and crack resistant abilities of natural tooth structure.
Publisher: American Physical Society (APS)
Date: 22-09-2009
Publisher: Elsevier BV
Date: 08-2012
DOI: 10.1016/J.ARCHORALBIO.2012.05.001
Abstract: To explore the possible role of functional stress in driving continuous post-eruptive emergence of teeth. A two dimensional finite element analysis model was established with a single mandibular premolar subjected to sagittal bending. Equivalent strain was charted for the inner and outer surfaces of the lamina dura, because bone deposition and resorption of this structure is confined to surface osteoblasts and osteoclasts. Bone disuse resorption was assumed to take place at equivalent strain values below 0.0008, while deposition was above 0.002. Strain in the periodontal ligament and principal stress throughout the model were also characterized. Strain analysis indicated bone maintenance for the lamina dura throughout most of the root length, but in both the apical and upper root regions, resorption was predicted for the outer surface, and bone deposition was predicted for the inner surface of the lamina dura. Strain in the periodontal ligament varied little with the exception of a marked increase close to the crown. Principal stress analysis revealed compression of the lower model border, with areas of increasing tension towards the upper model border. Strain from functional forces may continuously drive post-eruptive emergence of teeth through bony remodelling of the lamina dura, lifting teeth by both raising the apical lamina dura, and narrowing the upper root space to accommodate tapering root form. Such strain-driven bone turnover may contribute to pre-eruptive movement of teeth.
Publisher: Japanese Society for Dental Materials and Devices
Date: 2011
DOI: 10.4012/DMJ.2010-115
Abstract: The objective of this study was to assess the influence of the ceramic marginal angle on the length and nature of indentation cracks in ceramics near the ceramic/resin bonded interface. Disks of a leucite-reinforced ceramic or a diopside-based glass-ceramic bonded to a resin composite were sectioned so that the ceramic marginal angles were 45, 60, and 90°. Vickers indentations were placed in the ceramic at various distances from the bonded interface. The lengths of the indentation cracks running near parallel to the interface were measured and the orientation of crack propagation was characterized. The crack length and orientation were significantly affected by the distance from the interface and by the marginal angle, respectively. The crack length extended as the distance from the interface was shortened. Smaller marginal angles resulted in more oblique cracks. The toughness of the ceramic affected the indentation crack length, shape, and direction.
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.ACTBIO.2014.07.028
Abstract: Two approaches to measure the fracture energy to delaminate four different porcelains from zirconia substrates are compared using Schwickerath adhesion strength test specimens. In all instances it was possible to stably extend the crack along or adjacent to the porcelain-zirconia interface. The fracture energy expended to delaminate the porcelain was found by determining the work of fracture upon loading to 12 N and then unloading. Additional tests were undertaken on specimens notched along the interface, which enabled the compliance of the cracked Schwickerath specimens to be calibrated. The strain energy and deflection of the Schwickerath specimen as a function of crack length were derived. On this basis a simple expression was determined for the strain energy release rate or interfacial fracture toughness from the minima in the force-displacement curves. Consequently two measures of the adhesion energy were determined, the work of fracture and the strain energy release rate. It was found that the ranking for the four porcelains bonded to zirconia differed depending upon the approach. The work of fracture was substantially different from the strain energy release rate for three of the porcelain-zirconia systems and appears to be directly related to the residual stresses present in the bonded structures. The relative merits of the strain energy release rate, work of fracture vs. the stress to initiate cracking in the case of the Schwickerath adhesion test, are discussed. The advantage of this test is that it enables three estimates of the adhesion for porcelain veneers bonded to zirconia.
Publisher: Iron and Steel Institute of Japan
Date: 1989
Publisher: Wiley
Date: 04-1996
Publisher: AIP Publishing
Date: 21-01-2002
DOI: 10.1063/1.1436280
Abstract: The mechanical deformation of wurtzite GaN epilayers grown on sapphire substrates is studied by spherical indentation, cross-sectional transmission electron microscopy (XTEM), and scanning cathodoluminescence (CL) monochromatic imaging. CL imaging of indents which exhibit plastic deformation (based on indentation data) shows an observable “footprint” of deformation-produced defects that result in a strong reduction in the intensity of CL emission. Multiple discontinuities are observed during loading when the maximum load is above the elastic-plastic threshold, and such a behavior can be correlated with multiple slip bands revealed by XTEM. No evidence of pressure-induced phase transformations is found from within the mechanically damaged regions using selected-area diffraction patterns. The main deformation mechanism appears to be the nucleation of slip on the basal planes, with dislocations being nucleated on additional planes on further loading. XTEM reveals no cracking or delamination in any of the s les studied for loads of up to 250 mN.
Publisher: Elsevier BV
Date: 1996
Publisher: Elsevier BV
Date: 12-1995
Publisher: Springer Science and Business Media LLC
Date: 02-1993
Abstract: A simple model is described with which the entire force versus penetration behavior of indentation with a sphere, during loading and unloading, may be simulated from knowledge of the four test material parameters, Young's modulus, Poisson's ratio, flow stress at the onset of full plastic flow and strain hardening index, and the elastic properties of the indenter. The underlying mechanisms are discussed and the predictions of the model are compared with data produced by an ultra low load, penetration measuring instrument.
Publisher: Elsevier BV
Date: 1996
Publisher: Wiley
Date: 12-2005
DOI: 10.1111/J.1834-7819.2005.TB00368.X
Abstract: This study aimed to evaluate microhardness and chemical analysis of carious and caries-affected dentine. The hypothesis tested was that calcium:phosphorous (Ca:P) ratios correlate with microhardness values. Four carious human third molars were sectioned through the caries lesion in the mesiodistal longitudinal plane. One half of each lesion underwent carious dentine removal using Carisolv gel. The cut surfaces were polished, microhardness tested using an Ultra-Micro-Indentation System (UMIS) and elemental analysis performed using energy dispersive analysis of x-rays (EDAX). The microhardness of carious dentine decreased gradually towards the cavity floor, but that for caries-affected dentine showed more variation with depth, having a mean hardness of (0.63 +/- 0.18) GPa. Ca:P ratios of carious dentine varied among the four specimens. The mean Ca:P ratio of caries-affected dentine was 1:2.03 +/- 0.08. The hypothesis was accepted for active lesions. The use of Carisolv to excavate carious tissue can be as effective as rotary instrumentation.
Publisher: Wiley
Date: 22-11-2003
DOI: 10.1002/JBM.A.10361
Abstract: Over the past decade, orthopedic surgery has embraced an increase in the depth of cement penetration into the adjacent cancellous bone structure. The resultant interdigitation transforms this zone into a thick layer of continuous interpenetrating composite material. The failure behavior of the composite formed with a number of potential bone cements with different bonding ability was investigated. The cancellous bone-cement composites exhibit considerable resistance to crack extension, and in situ optical observation indicates that the contribution of the cancellous bone is analogous to that of a typical fiber bridging process. The critical stress intensity factor and the work of fracture have been used to quantify the failure characteristics of the cancellous bone-cement composites. The nature of the crack propagation through these cement-bone composites was also captured via optical microscopy, and scanning electron microscopic images were taken of the failure surfaces. The R-curve behavior, or crack extension characteristic, of the cancellous bone-cement composite was also determined. The interesting outcome is that the cancellous bone-PMMA (poly-methylmethacrylate) composite, despite the absence of chemical bonding with bone, required the highest energy to fracture. In addition, the dimensional stability of the cement has a great effect on the interface.
Publisher: Springer Science and Business Media LLC
Date: 2002
Abstract: The mechanical properties of glass-ionomer cements (GICs) have been satisfactory for dental applications and have shown their potential in orthopedic surgery. Because the physiological environment in orthopedics is different from dentistry by unavoidable contamination with blood and other fluids such as normal saline used during an operation, the determination of GICs for orthopedic applications should be performed in an appropriate environment. The properties of a novel resin-modified GIC, S430, for orthopedic applications were evaluated in simulated orthopedic conditions by an early exposure to and long-term storage in normal saline. An early exposure to normal saline caused 20-60% reduction of its compressive and flexural properties, whereas long-term storage in normal saline showed slight changes of its mechanical properties. The effects were probably due to the disturbance of the cross-linking formation in the acid-base reaction and also the reduction of electrostatic interactions of the cross-linking polymeric chain of hydroxyethyl methacrylate (HEMA) in resin-modified GIC.
Publisher: Wiley
Date: 09-1975
DOI: 10.1111/J.1151-2916.1975.TB19001.X
Abstract: Studies were continued on the effects of surface‐active environments on the hardness and the rates of drilling and abrasive wear of mono‐ and polycrystalline Al 2 O 3 . Changes in hardness induced by n ‐alcohols and various aqueous environments were correlated with changes in ζ‐potential, hardness being maximum at the point of zero charge (pzc). Diamond‐core drilling rates exhibited a similar relation. Studies of the environment‐sensitive abrasive wear of both mono‐ and polycrystalline Al 2 O 3 on a diamond‐impregnated metallographic wheel revealed more complicated behavior. The wear rate of Al 2 O 3 under n ‐alcohols is markedly dependent on the viscosity of the environment, with little or no correlation with ζ‐potential being evident. Studies using methanol‐water mixtures indicated, on the other hand, a slight viscosity dependence and the converse correlation with ζ‐potential to that observed in diamond‐core drilling, i.e. the rate of material removal was lowest at the pzc. Tests in aqueous solutions revealed no dependence on viscosity, but a strong inverse dependence on ζ‐potential, wear rate again being lowest at the pzc. These and other results are interpreted in terms of the various influences of adsorbed species on the near‐surface flow and fracture behavior of Al 2 O 3 .
Publisher: Quintessence Publishing
Date: 2013
DOI: 10.11607/JOMI.3019
Abstract: The purpose of this study was to compare the stress and strain occurring in peri-implant bone and implants used to support maxillary overdentures. Three-dimensional finite element analysis (3D FEA) was used to compare one-piece zirconia and titanium implants. Two types of implants were simulated using a 3D FEA model: one-piece zirconia and titanium implants (diameter, 3.8 × 11.5 mm) with 2.25-mm diameter ball abutments. In each simulation four implants were placed bilaterally in the canine remolar region of an edentulous maxillary model. Static loads were applied axially and 20 degrees buccolingually on the buccal slope of the lingual cusps of posterior teeth of the first quadrant. Von Mises stresses and equivalent strains generated in peri-implant bone and first principal stresses in the implants were calculated. Comparable stress and strain values were shown in the peri-implant bone for both types of implants. The maximum equivalent strain produced in the peri-implant region was mostly within the range for bone augmentation. Under oblique loading, maximum von Mises stresses and equivalent strain were more evident at the neck of the most distal implant on the loaded side. Under axial load, the stress and strain were transferred to the peri-implant bone around the apex of the implant. Maximum tensile stresses that developed for either material were well below their fracture strength. The highest stresses were mainly located at the distobuccal region of the neck for the two implant materials under both loading conditions. From a biomechanical point of view, ceramic implants made from yttrium-stabilized tetragonal polycrystalline zirconia may be a potential alternative to conventional titanium implants for the support of overdentures. This is particularly relevant for a select group of patients with a proven allergy to titanium. Prospective clinical studies are still required to confirm these in vitro results. Different simulations presenting various cortical bone thicknesses and implant designs are required to provide a better understanding of the biomechanics of zirconia implants.
Publisher: Elsevier BV
Date: 11-2018
DOI: 10.1016/J.DENTAL.2018.08.294
Abstract: To provide insight of the setting reactions of Biodentine™, a hydraulic calcium silicate cement, based upon observations using Fourier Transform Infra-Red (FTIR) spectroscopy. FTIR spectra of components before and during the setting reaction were taken using the attenuated total reflectance (ATR) technique. Measurements over wavelengths 600-4000cm FTIR spectrum of Biodentine™ powder revealed a number of peaks from 650 to 1100cm FTIR can be used to follow the chemical reactions in dental cements and provides insight into the relatively slow setting reactions of hydraulic calcium silicate cements.
Publisher: Elsevier BV
Date: 04-2009
DOI: 10.1016/J.DENTAL.2008.10.008
Abstract: Polymerization contraction of dental composite produces a stress field in the bonded surrounding substrate that may be capable of propagating cracks from pre-existing flaws. The objectives of this study were to assess the extent of crack propagation from flaws in the surrounding ceramic substrate caused by composite contraction stresses, and to propose a method to calculate the contraction stress in the ceramic using indentation fracture. Initial cracks were introduced with a Vickers indenter near a cylindrical hole drilled into a glass-ceramic simulating enamel. Lengths of the radial indentation cracks were measured. Three composites having different contraction stresses were cured within the hole using one- or two-step light-activation methods and the crack lengths were measured. The contraction stress in the ceramic was calculated from the crack length and the fracture toughness of the glass-ceramic. Interfacial gaps between the composite and the ceramic were expressed as the ratio of the gap length to the hole perimeter, as well as the maximum gap width. All groups revealed crack propagation and the formation of contraction gaps. The calculated contraction stresses ranged from 4.2 MPa to 7.0 MPa. There was no correlation between the stress values and the contraction gaps. This method for calculating the stresses produced by composites is a relatively simple technique requiring a conventional hardness tester. The method can investigate two clinical phenomena that may occur during the placement of composite restorations, i.e. simulated enamel cracking near the margins and the formation of contraction gaps.
Publisher: AIP Publishing
Date: 10-04-2002
DOI: 10.1063/1.1469660
Abstract: The deformation mechanisms of crystalline (100) Ge were studied using nanoindentation, cross sectional transmission electron microscopy (XTEM) and Raman microspectroscopy. For a wide range of indentation conditions using both spherical and pointed indenters, multiple discontinuities were found in the force–displacement curves on loading, but no discontinuities were found on unloading. Raman microspectroscopy, measured from s les which had plastically deformed on loading, showed a spectrum shift from that in pristine Ge, suggesting only residual strain. No evidence (such as extra Raman bands) was found to suggest that any pressure-induced phase transformations had occurred, despite the fact that the material had undergone severe plastic deformation. Selected area diffraction pattern studies of the mechanically damaged regions also confirmed the absence of additional phases. Moreover, XTEM showed that, at low loads, plastic deformation occurs by twinning and dislocation motion. This indicates that the hardness of Ge measured by indentation is not primarily dominated by phase transformation, rather by the nucleation and propagation of twin bands and/or dislocations.
Publisher: Elsevier
Date: 2008
Publisher: Wiley
Date: 30-08-2016
DOI: 10.1111/ADJ.12376
Abstract: Collagen type I, proteoglycans (PG) and non-collagenous proteins represent important building blocks of the dentine matrix. While different PGs have been identified in dentine, changes in the distribution of these macromolecules with the progression of caries have been poorly characterized. The aim of this study was to compare the immunolocalization of three small collagen-binding PGs (biglycan, fibromodulin and lumican) as well as collagen (types I and VI) in healthy versus carious dentine. Longitudinal demineralized sections of extracted teeth were stained with antibodies recognizing specific PG core proteins and collagens, as well as glycosaminoglycans (GAGs) with toluidine blue. In healthy dentine, PGs appeared to be more abundant near the tubule walls and directly under the cusps. Conversely, in carious dentine, specific locations appeared to be more prone to PG degradation than others. These degradation patterns were well correlated with the progression of caries into the tissue, and also appeared to trigger interesting morphological changes in the tissue structure, such as the deformation of dentine tubules near highly infected areas and the lower concentration of PG in tertiary dentine. This study presents new insights into the involvement of PGs in the progression of caries.
Publisher: Elsevier BV
Date: 1997
Publisher: Elsevier BV
Date: 07-2007
DOI: 10.1016/J.DENTAL.2006.06.022
Abstract: To determine the adhesion at the titanium-porcelain interface using a fracture mechanics approach, and to investigate the bonding mechanism using SEM. Specimens of five different titanium-porcelain and one base metal-porcelain bonding systems were prepared for a four-point bending interfacial delaminating test on a universal testing machine. The pre-cracked specimen was subjected to load and the strain energy release rate (G, J/m(2)) was calculated from the critical load to induce stable crack extension in each system. The interface for the various materials was investigated in an SEM and compared. The titanium-porcelain with Gold Bonder showed the highest G-value (72.39+/-13.21J/m(2)) among the groups whilst titanium-porcelain with cross-cut-bur preparation showed the lowest (5.78+/-1.39J/m(2)). The former was significantly higher than that of Wiron 99 (base-metal, BEGO, Germany) porcelain (40.01+/-6.67J/m(2)), a clinically accepted bonding system for many years. The G-values of porcelain fused to titanium-Rocatec, titanium-sandblasted and/or titanium-GC-Bonder were 10.81+/-1.49, 12.64+/-3.01 and 35.74+/-5.20J/m(2), respectively. SEM images of the interface fracture crack path for the different bonders enabled the mechanisms responsible for the differences in strain energy release rates to be appreciated. The strain energy release rate (G) of titanium-porcelain with a Gold Bonder interface layer was highest among the five different systems.
Publisher: Elsevier BV
Date: 2016
DOI: 10.1016/J.DENTAL.2015.09.009
Abstract: This paper investigates the structure and some properties of resin infiltrated ceramic network structure materials suitable for CAD/CAM dental restorative applications. Initially the basis of interpenetrating network materials is defined along with placing them into a materials science perspective. This involves identifying potential advantages of such structures beyond that of the in idual materials or simple mixing of the components. Observations from a number of recently published papers on this class of materials are summarized. These include the strength, fracture toughness, hardness and damage tolerance, namely to pointed and blunt (spherical) indentation as well as to burr adjustment. In addition a summary of recent results of crowns subjected to simulated clinical conditions using a chewing simulator are presented. These results are rationalized on the basis of existing theoretical considerations. The currently available ceramic-resin IPN material for clinical application is softer, exhibits comparable strength and fracture toughness but with substantial R-curve behavior, has lower E modulus and is more damage tolerant than existing glass-ceramic materials. Chewing simulation observations with crowns of this material indicate that it appears to be more resistant to sliding/impact induced cracking although its overall contact induced breakage load is modest.
Publisher: IOP Publishing
Date: 08-12-2004
DOI: 10.1088/0967-3334/25/1/009
Abstract: A novel instrument has been devised for the in vivo examination of the dynamic biomechanical properties of skin. These properties include stiffness and viscoelasticity. The advantage of the device is its ability to examine the skin dynamically, thereby eliminating preconditioning effects. Furthermore, it is portable, hand-held and easy to operate in the clinical environment. The objective of this study was to determine the accuracy and reliability of the dynamic biomechanical skin measurement (DBSM) probe. The accuracy was determined by examining a series of silicone elastomer specimens. A comparison of the shear modulus (G*), obtained from a static indentation system, with stiffness, obtained from the DBSM probe, was performed. The reliability was determined by examining both silicone elastomers and forearm volar skin in vivo. In both cases assessment was by six different operators (inter-reliability) and also by an in idual operator (intra-reliability). Statistical analysis was performed using Levene's test of homogeneity and analysis of variance to ascertain if there were significant differences between operators (inter-reliability) and with one in idual operator (intra-reliability). It can be concluded, from this study, that the DBSM probe is accurate (R2 = 0.96, p = 0.01). It is also inter- and intra-reliable when assessing elastomer stiffness and skin stiffness. However, phase lag was not found to be a useful indicator of device reliability. It is anticipated that this device will be used to examine dermatological conditions and the benefits, or otherwise, of treatment. The DBSM probe promises to contribute to the objective measurement of physical properties of the skin in future investigative studies.
Publisher: Wiley
Date: 26-01-2013
DOI: 10.1111/J.1600-0501.2011.02411.X
Abstract: Two fractured one-piece experimental (commercially unavailable) zirconia implants were analyzed using scanning electron microscope (SEM) analysis to identify failure origins and aid in understanding the failure mechanisms. Modifications to the zirconia implant design are suggested to minimize such fracture incidences. Two zirconia implants fractured during the final torquing in the maxillary ridge using the prescribed hand torque wrench. The implants were subsequently retrieved and prepared for optical and SEM evaluation. Critical attention was given to the fractography (crack morphology) of the fractured implants to identify the fracture origin. Events related to initiation and propagation of the crack front could be detected from the morphology of the fractured surfaces. Unfavorable torque and bending forces applied on the implant during surgical placement and the inherent flaws in the material may have resulted in crack initiation and implant failure. Caution must be exercised when placing zirconia implants in dense bone sites. Modification of surgical protocols for the intended implant site may be necessary. Improvement in design features specific to zirconia implants, and strict quality control during manufacture is essential to minimize the likelihood of fracture.
Publisher: Elsevier BV
Date: 07-2017
DOI: 10.1016/J.JBIOMECH.2017.06.012
Abstract: The aim of this study is to investigate the biomechanics for orthodontic tooth movement (OTM) subjected to concurrent single-tooth vibration (50Hz) with conventional orthodontic force application, via a clinical study and computational simulation. Thirteen patients were recruited in the clinical study, which involved distal retraction of maxillary canines with 1.5N (150g) force for 12weeks. In a split mouth study, vibration and non-vibration sides were randomly assigned to each subject. Vibration of 50Hz, of approximately 0.2N (20g) of magnitude, was applied on the buccal surface of maxillary canine for the vibration group. A mode-based steady-state dynamic finite element analysis (FEA) was conducted based on an anatomically detailed model, complying with the clinical protocol. Both the amounts of space closure and canine distalization of the vibration group were significantly higher than those of the control group, as measured intra-orally or on models (p<0.05). Therefore it is indicated that a 50Hz and 20g single-tooth vibration can accelerate maxillary canine retraction. The volume-average hydrostatic stress (VHS) in the periodontal ligament (PDL) was computationally calculated to be higher with vibration compared with the control group for maxillary teeth and for both linguo-buccal and mesial-distal directions. An increase in vibratory frequency further lified the PDL response before reaching a local natural frequency. An lification of PDL response was also shown to be induced by vibration based on computational simulation. The vibration-enhanced OTM can be described by mild, vigorous and diminishing zones among which the mild zone is considered to be clinically beneficial.
Publisher: Springer Science and Business Media LLC
Date: 03-1988
DOI: 10.1007/BF01154016
Publisher: Elsevier BV
Date: 2006
Publisher: Springer Science and Business Media LLC
Date: 13-11-2007
DOI: 10.1007/S00455-007-9126-Z
Abstract: This article introduces a new way of recording intraoral pressures from a range of locations within the oral cavity. To measure pressure flow dynamics during swallowing, we fitted eight miniature pressure transducers capable of measuring absolute pressures to a chrome-cobalt palatal appliance with a labial bow. Unlike previous devices, our design provides a rigid, custom-fitted platform for the simultaneous recording of pressures at eight locations within the oral cavity during function. We placed an anterior pair of gauges to measure lingual and labial contact against the left central incisor tooth, and two pairs of gauges to measure pressure contributions of the lateral tongue margin and cheeks on the canine and first molar teeth. Finally, lingual pressure on the midline of the palate was measured by two gauges, one at the position of the premolars and one on the posterior boundary of the hard palate. We then recorded intraoral pressures in five adult volunteers seated in an upright position and asked to swallow 10 ml of water. Labial pressures on the canine rose rapidly from a resting level of 10 kPa to 33 kPa, while pressure profiles from the labial aspects of the incisor and first molar teeth followed a negative pattern, peaking at -12 kPa for the incisor and -15 kPa for the molar sensor. Pressure profiles recorded from the palatal aspects of the first molar and the canine appeared to be similar, but the former fell to -13 kPa before rising to 9 kPa, and the canine pressure rapidly increased to 22 kPa before returning to its resting level of 4 kPa. The pressure profile of the palatal aspect of the central incisor was strikingly different at the start of the swallow, pressure dropped precipitously to -20 kPa, before slowly rising to 10 kPa. It then followed the general pattern of the other two sensors, before peaking again at 10 kPa and then returning to a resting level of 4 kPa. We also showed that there were significant negative pressures in the mouth during function, and that pressure profiles varied markedly between in iduals.
Publisher: Informa UK Limited
Date: 14-02-2010
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.DENTAL.2015.10.010
Abstract: The objective of this study was to identify the different microstructures produced by CC, PM and as-cast techniques for Co-Cr alloys and their phase stability following porcelain firings. Three bi-layer porcelain veneered Co-Cr specimens and one monolithic Co-Cr specimen of each alloy group [cast, powder metallurgy (PM), CAD/CAM (CC)] were manufactured and analyzed using electron backscatter diffraction (EBSD), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Specimens were treated to incremental numbers of porcelain firings (control 0, 5, 15) with crystallographic data, grain size and chemical composition subsequently obtained and analyzed. EBSD datasets of the cast alloy indicated large grains >200 μm whereas PM and CC alloy consisted of mean arithmetic grain sizes of 29.6 μm and 19.2 μm respectively. XRD and EBSD results both indicated the highest increase in hcp content (>13vol%) for cast Co-Cr alloy after treatment with porcelain firing while PM and CC indicated .05) was observed in CC. EDS line scans indicated an increase in Cr content at the alloy surface after porcelain firing treatment for all three alloys. PM and CC produced alloy had superior fcc phase stability after porcelain firings compared to a traditional cast alloy. It is recommended that PM and CC alloys be used for porcelain-fused-to-metal restorations.
Publisher: Springer Science and Business Media LLC
Date: 1997
Publisher: Elsevier BV
Date: 06-2014
DOI: 10.1016/J.JMBBM.2014.02.002
Abstract: To determine the contact response and damage tolerance or strength degradation of a range of dental CAD/CAM ceramic materials including novel polymer-infiltrated-ceramic-network (PICN) materials by means of spherical indentations at various loads and indenter radii. The seven tested materials included Mark II, PICN test materials 1 and 2, In-Ceram Alumina, VM 9, In-Ceram YZ (Vita Zahnfabrik, Bad Saeckingen, Germany) and IPS e.max CAD, (Ivoclar Vivadent, Schaan, Liechtenstein). To evaluate the damage tolerance and role of indenter size, indentations with tungsten carbide spheres (0.5mm and 1.25mm radius) were placed on bending bars with varying loads (1.96-1000N). The indented bending bars were subsequently loaded to fracture in three-point bending. The contact induced damage was analyzed by light microscopy (LM) and SEM. The spherical contact response was measured on polished surfaces. The initial strengths for the in idual materials were found to reduce above specific indentation loads, which were a function of the indenter radius. Employing a 0.5mm radius sphere resulted in the following strength degrading loads and ordering of materials: VM9 (98N)<MarkII-PICN1 (147N)<ICAlumina-e.maxCAD (300N)<PICN2-YTZP (500N). For the materials indented with the 1.25mm sphere, higher loads were required for the onset of strength degradation: VM9 (190N)<MarkII (300N)<PICN1 (400N)<e.maxCAD (500N)<ICAlumina (700N)<PICN2 (1000N)<YTZP (above 1000N). Two different damage modes were observed by SEM and LM - brittle cone cracking and plastic deformation. The PICN materials exhibited elastic-plastic behavior with creep. In contrast YTZP showed entirely elastic behavior upon loading with both spheres. This study aims to emulate the likely clinical behavior of contact loading by opposing cusps to dental restorative ceramic materials by utilizing spherical indentations at various loads and sphere diameters.
Publisher: Elsevier BV
Date: 09-1996
Publisher: Elsevier BV
Date: 05-2013
Publisher: Springer Science and Business Media LLC
Date: 12-2009
DOI: 10.4248/IJOS09031
Publisher: Elsevier BV
Date: 07-2007
DOI: 10.1016/J.DENTAL.2006.06.017
Abstract: The aim of the study is to investigate the stress-strain response of different dental materials, especially dental brittle materials, and compare them with enamel. A nano-based indentation system (Ultra Micro-Indentation System, UMIS-2000, CSIRO, Australia) was used to determine the indentation stress-strain response of two kinds of dental ceramics (Cerec 2 Mark II and Vita VM9), one kind of dental alloy (Wiron 99) and healthy enamel. A spherical indenter was used to test the materials with nanometer and micro-Newton displacement and force resolution. Assuming the elastic modulus remained constant, a plot of contact pressure versus contact strain, H-a/R, of each material was obtained. By comparing the H-a/R curve of the different materials with enamel, it can be concluded that only the metallic alloy, has similar stress-strain response as enamel. Dental ceramics showed much higher yield stress response than enamel. VM9, a porcelain veneer component of crown/bridge structure, is slightly softer than its core, Mark II. The yield point for Mark II and VM9 are nearly 10 and 7GPa, respectively, and approximately 2GPa for Wiron alloy and enamel. H-a/R curves provide a new method to compare the mechanical properties of different dental materials. From the standpoint of structural reliability, strong and tough materials with primarily elastic response, such as toughened ceramics are required to enable dental crown/bridges to have long term reliability. On the other hand, materials with too high hardness or yield response may damage opposing teeth during occlusal contact. Future studies may establish a relationship between stress and strain property and abrasive wear of dental material.
Publisher: Elsevier BV
Date: 02-2009
DOI: 10.1016/J.AJODO.2007.03.032
Abstract: The initial mechanical response to orthodontic loading comprises biologic reactions that remain unclear, despite their clinical significance. We used a 3-dimensional finite element analysis to investigate the stress-strain responses of teeth to orthodontic loading. The model was derived from computed tomography data, with adequate boundary conditions and tissue characterization, with orthodontic hardware to provide a more accurate reflection of events during orthodontic therapy. This study also incorporated the adjacent dentition. Two cases were analyzed: a single-tooth system with a mandibular canine, and a multi-tooth system consisting of the mandibular incisor, the canine, and the first premolar, subjected to orthodontic tipping forces. The systems experienced elevated distortion strain energies in the alveolar crest, whereas the tensile and compressive stresses coincided with the apical sites clinically associated with root resorption. Stress levels were considerably greater in the multi-tooth system than in the single-tooth system. The results for the single-tooth model agree with those previously reported. The numeric studies show how orthodontic tooth movement develops different stress fields and how root resorption might occur as a result of hydrostatic compressive stress-induced tissue necrosis.
Publisher: IOP Publishing
Date: 2011
Publisher: Elsevier BV
Date: 07-2013
DOI: 10.1016/J.ARCHORALBIO.2012.12.003
Abstract: (1) Mammalian teeth play a major role in food acquisition and processing. While most mammals are heterodont and masticate their food, dolphins are homodont with simplified tooth morphology and negligible mastication. Understanding mechanical properties of dental tissues in dolphins is fundamental to elucidate the functional morphology and biomechanics of their feeding apparatus. This paper aims to study the hardness and elastic modulus of enamel and dentine in dolphins. (2) Teeth of 10 extant species (Inioidea and Delphinoidea) were longitudinally sectioned, polished and mounted in a UMIS nanoindenter. Indentations were performed from dentine to outer enamel. Hardness and elastic modulus were calculated using the Oliver-Pharr method. (3) Mean values of hardness and elastic modulus were similar on buccal and lingual surfaces. While dentine hardness was statistically similar among species, enamel hardness varied from 3.86GPa (±0.4) in Steno bredanensis (rough-toothed dolphin) to 2.36GPa (±0.38) in Pontoporia blainvillei (franciscana). For most species, there was a gradational increase in hardness values from inner to outer enamel. Enamel and dentine elastic modulus values clearly differed among species. In enamel, it ranged from 69.32GPa (±4.08) in the rough-toothed dolphin to 13.51GPa (±2.80) in Stenella coeruleoalba (striped dolphin). For most species, elastic modulus values were highest at inner and outer enamel. (4) Differences in mechanical properties between species, and within the enamel of each species, suggest functional implications and influence of ultrastructural arrangement and chemical composition.
Publisher: Elsevier BV
Date: 02-2012
DOI: 10.1016/J.MICRON.2011.08.003
Abstract: Dentin is a mineralized dental tissue underlying the outer enamel that has a peculiar micro morphology. It is composed of micrometer sized tubules that are surrounded by a highly mineralized structure, called peritubular dentin (PTD), and embedded in a collagen-rich matrix, named intertubular dentin. The PTD has been thought to be composed of a highly mineralized collagen-free organic matrix with unknown composition. Here we tested the hypothesis that proteoglycans and glycosaminoglycans, two important organic structural features found in dentin, are key participants in the microstructure and composition of the PTD. To test this hypothesis dentin blocks were demineralized with 10 vol% citric acid for 2 min and either digested with 1mg/ml TPCK-treated trypsin with 0.2 ammonium bicarbonate at pH 7.9 (TRY) or 0.1 U/mL C-ABC with 50mM Tris, 60mM sodium acetate and 0.02% bovine serum albumin at pH 8.0 (C-ABC). TRY is known to cleave the protein core of dentin proteoglycans, whereas C-ABC is expected to selectively remove glycosaminoglycans. All specimens were digested for 48 h in 37°C, dehydrated in ascending grades of acetone, immersed in HMDS, platinum coated and imaged using an FE-SEM. Images of demineralized dentin revealed a meshwork of noncollagenous fibrils protruding towards the tubule lumen following removal of the peritubular mineral and confirmed the lack of collagen in the peritubular matrix. Further, images revealed that the peritubular organic network originates from a sheet-like membrane covering the entire visible length of tubule, called lamina limitans. Confirming our initial hypothesis, after the digestion with C-ABC the organic network appeared to vanish, while the lamina limitans was preserved. This suggests that glycosaminoglycans are the main component of the PTD organic network. Following digestion with TRY, both the organic network and the lamina limitans disappeared, thus suggesting that the lamina limitans may be primarily composed of proteoglycan protein cores. In summary, our results provide novel evidence that (1) PTD lacks collagen fibrils, (2) PTD contains an organic scaffold embedded with mineral and (3) the PTD organic matrix is manly composed of glycosaminoglycans, whereas the lamina limitans is primarily made of proteoglycans protein cores.
Publisher: Informa UK Limited
Date: 2001
DOI: 10.1080/10255840008907999
Abstract: Several pre-existing anterior and posterior dental bridge models using Finite elements and the new ceramic material In-Ceram have been developed. The mechanical behaviour of these models has been compared with optimised profiles obtained from a newly developed evolutionary algorithm known as Evolutionary Structural Optimisation (ESO). The results show that the mechanical behaviour of the bridges was mainly restricted by the properties of the porcelain veneer and the design of the bridges themselves. For the case of the anterior bridge, it was found that there existed a specific thickness of veneer that minimised the maximum principal stress. This was related to peak stresses that occurred at the bridge surface. Peak stresses also occurred in the material interface between the In-Ceram and the veneer. These extreme stresses were attributed to the notch size and shape. For the case of the posterior bridge, it was concluded that the shape of the bottom of the Pontic tooth is crucial in reducing the magnitude of the maximum principal tensile stress. The ESO process produced bridge designs which have uniformly stressed bridge surfaces, and which also have significantly lower maximum principal tensile stresses compared to the pre-existing designs (up to 44%).
Publisher: The Royal Society
Date: 06-06-2016
Abstract: A mammalian tooth is abraded when a sliding contact between a particle and the tooth surface leads to an immediate loss of tooth tissue. Over time, these contacts can lead to wear serious enough to impair the oral processing of food. Both anatomical and physiological mechanisms have evolved in mammals to try to prevent wear, indicating its evolutionary importance, but it is still an established survival threat. Here we consider that many wear marks result from a cutting action whereby the contacting tip(s) of such wear particles acts akin to a tool tip. Recent theoretical developments show that it is possible to estimate the toughness of abraded materials via cutting tests. Here, we report experiments intended to establish the wear resistance of enamel in terms of its toughness and how friction varies. Imaging via atomic force microscopy (AFM) was used to assess the damage involved. Damage ranged from pure plastic deformation to fracture with and without lateral microcracks. Grooves cut with a Berkovich diamond were the most consistent, suggesting that the toughness of enamel in cutting is 244 J m −2 , which is very high. Friction was higher in the presence of a polyphenolic compound, indicating that this could increase wear potential.
Publisher: Springer Science and Business Media LLC
Date: 12-1991
DOI: 10.1007/BF02402675
Publisher: Springer Science and Business Media LLC
Date: 29-04-2014
DOI: 10.1007/S10856-014-5217-1
Abstract: The role of surface preparation, hydrothermal ageing exposure and subsequent cyclic fatigue testing on the biaxial strength of a dental Y-TZP material are investigated. The initial strength and survival rate of a dental Y-TZP ceramic material to fatigue testing was found to be highly dependent upon surface preparation more so than exposure to various hydrothermal exposure conditions. The results suggest that the monoclinic phase generated by either surface damage (especially sandblasting) and to a lesser extent hydrothermal exposure does appear to mitigate strength and fatigue degradation. The results are discussed in terms of the size of defects generated following various surface treatments and the role of cyclic fatigue induced crack growth. A critical ratio is established between the monotonic strength and fatigue stress survival. From the specimens that failed and exhibited reduced strength after cycling a plot of averaged crack growth rate versus max cyclic stress intensity factor was established which closely matched existing results for Y-TZP ceramics.
Publisher: Elsevier BV
Date: 06-2011
DOI: 10.1016/J.DENTAL.2011.02.002
Abstract: To evaluate the mechanical behavior of a prototype porous ceramic interpenetrating polymer-ceramic material containing 15-20% polymer. After s le preparation, elastic modulus, hardness, stress-strain relationship and indentation creep response were measured by a nanoindentation system. Fracture toughness was measured by the single-edge-notched beam (SENB) method. SEM was employed to observe the fractured surface and analyze the fracture mechanisms. The polymer infiltrated ceramic material has elastic modulus, hardness, and fracture toughness values of 30.14GPa, 2.59GPa, and 1.72 MPam(1/2), respectively. The material illustrates a significant indentation size effect for elastic modulus and hardness, and has similar indentation creep behavior to human enamel. Manufacturing procedures such as the density of pre-infiltrated porous ceramic and processing pressure influence the final properties of the material. This polymer infiltrated ceramic material is anticipated to become a new member of the dental CAD/CAM family.
Publisher: Springer Science and Business Media LLC
Date: 15-09-2017
DOI: 10.1007/S10237-016-0826-X
Abstract: This paper aimed to develop a clinically validated bone remodeling algorithm by integrating bone's dynamic properties in a multi-stage fashion based on a four-year clinical follow-up of implant treatment. The configurational effects of fixed partial dentures (FPDs) were explored using a multi-stage remodeling rule. Three-dimensional real-time occlusal loads during maximum voluntary clenching were measured with a piezoelectric force transducer and were incorporated into a computerized tomography-based finite element mandibular model. Virtual X-ray images were generated based on simulation and statistically correlated with clinical data using linear regressions. The strain energy density-driven remodeling parameters were regulated over the time frame considered. A linear single-stage bone remodeling algorithm, with a single set of constant remodeling parameters, was found to poorly fit with clinical data through linear regression (low [Formula: see text] and R), whereas a time-dependent multi-stage algorithm better simulated the remodeling process (high [Formula: see text] and R) against the clinical results. The three-implant-supported and distally cantilevered FPDs presented noticeable and continuous bone apposition, mainly adjacent to the cervical and apical regions. The bridged and mesially cantilevered FPDs showed bone resorption or no visible bone formation in some areas. Time-dependent variation of bone remodeling parameters is recommended to better correlate remodeling simulation with clinical follow-up. The position of FPD pontics plays a critical role in mechanobiological functionality and bone remodeling. Caution should be exercised when selecting the cantilever FPD due to the risk of overloading bone resorption.
Publisher: Wiley
Date: 16-09-2012
DOI: 10.1111/J.1365-2842.2011.02257.X
Abstract: Tooth wear has been recognised as a major problem in dentistry. Epidemiological studies have reported an increasing prevalence of tooth wear and general dental practitioners see a greater number of patients seeking treatment with worn dentition. Although the dental literature contains numerous publications related to management and rehabilitation of tooth wear of varying aetiologies, our understanding of the aetiology and pathogenesis of tooth wear is still limited. The wear behaviour of dental biomaterials has also been extensively researched to improve our understanding of the underlying mechanisms and for the development of restorative materials with good wear resistance. The complex nature of tooth wear indicates challenges for conducting in vitro and in vivo wear investigations and a clear correlation between in vitro and in vivo data has not been established. The objective was to critically review the peer reviewed English-language literature pertaining to prevalence and aetiology of tooth wear and wear investigations in dentistry identified through a Medline search engine combined with hand-searching of the relevant literature, covering the period between 1960 and 2011.
Publisher: Springer Science and Business Media LLC
Date: 2002
Abstract: In vivo biocompatibility of glass ionomer cements (GICs) was evaluated for use in orthopaedic surgery using a rat model and compared with conventional bone cement, Polymethyl methacrylate, PMMA. The unset GICs and PMMA were inserted into the marrow cavities of rat femora and retained in situ for various periods of time. The PMMA bone cement showed complete biocompatibility with no interference with reparative bone. The conventional GIC with smaller glass particles and lower powder/liquid ratio showed an initial minor toxic effect on rat bone tissue with later disturbance of adjacent bone formation. The conventional GIC with larger-size glass particles and higher powder/liquid ratio and resin-modified GIC showed more severe toxic effect on rat tissue with the resin-modified GIC affecting the rat bone tissue later. The causes of toxicity associated with the conventional GIC with larger glass particles and higher powder/liquid ration and the resin-modified GIC are thought to be related with the unreacted acid component of both materials and longer ongoing metallic ion release.
Publisher: Mary Ann Liebert Inc
Date: 02-2023
Publisher: Elsevier BV
Date: 12-2012
DOI: 10.1016/J.MICRON.2012.03.021
Abstract: In this study we sought to gain insights of the structural and mechanical heterogeneity of dentin at different length scales. We compared four distinct demineralization protocols with respect to their ability to expose the periodic pattern of dentin collagen. Additionally, we analyzed the phase contrast resulting from AFM images obtained in tapping mode to interrogate the viscoelastic behavior and surface adhesion properties of peritubular and intertubular dentin, and partially demineralized dentin collagen fibrils, particularly with respect to their gap and overlap regions. Results demonstrated that all demineralization protocols exposed the gap and overlap zones of dentin collagen fibrils. Phase contrast analyses suggested that the intertubular dentin, where the organic matrix is concentrated, generated a higher phase contrast due a higher contribution of energy dissipation (d ing) than the highly mineralized peritubular region. At increasing litudes, viscoelasticity appeared to play a more significant contribution to the phase contrast of the images of collagen fibrils. The overlap region yielded a greater phase contrast than the more elastic gap zones. In summary, our results contribute to the perspective that, at different length scales, dentin is constituted of structural features that retain heterogeneous mechanical properties contributing to overall mechanical performance of the tissue. Furthermore, the interpretation of phase contrast from images generated with AFM tapping mode appears to be an effective tool to gain an improved understanding of the structure and property relationship of biological tissues and biomaterials at the micro- and nano-scale.
Publisher: Springer Science and Business Media LLC
Date: 12-1986
DOI: 10.1007/BF01729403
Publisher: Elsevier BV
Date: 2006
DOI: 10.1016/J.JBIOMECH.2005.05.022
Abstract: The chin is a feature unique to humans. This study evaluates the effect of mandibular symphyseal design on biomechanical masticatory effectiveness as determined by structural stiffness and stress developed under flexural and torsional loading. A simple model of three symphyseal shapes (chin, flat symphysis and lingual buttress), was built to represent human, Neanderthal and higher primate symphyses and these were subjected to wishboning and torsional forces. Additionally, an anatomically detailed reconstruction was made of the CT scan of an actual human mandible, which was then also morphed into a chinless model. The results of a 3-D finite element analysis show firstly, that none of the three different symphyseal shapes is biomechanically more advantageous than the others for the given loading condition. Secondly, we show in a CT-derived model, that the presence of a chin does not confer significantly improved stiffness to torsional or flexural loading. These results indicate that the acquisition of a chin in modern humans is not related to the functional demands placed upon the mandible during mastication, but suggest that it may have developed in response to other biomechanical demands.
Publisher: Elsevier BV
Date: 1992
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.JBIOMECH.2015.10.019
Abstract: Despite the importance of dynamic behaviors of dental and periodontal structures to clinics, the biomechanical roles of anatomic sophistication and material properties in quantification of vibratory characteristics remain under-studied. This paper aimed to generate an anatomically accurate and structurally detailed 3D finite element (FE) maxilla model and explore the dynamic behaviors of human teeth through characterizing the natural frequencies (NFs) and mode shapes. The FE models with different levels of structural integrities and material properties were established to quantify the effects of modeling techniques on the computation of vibratory characteristics. The results showed that the integrity of computational model considerably influences the characterization of vibratory behaviors, as evidenced by declined NFs and perceptibly altered mode shapes resulting from the models with higher degrees of completeness and accuracy. A primary NF of 889Hz and the corresponding mode shape featuring linguo-buccal vibration of maxillary right 2nd molar were obtained based on the complete maxilla model. It was found that the periodontal ligament (PDL), a connective soft tissue, plays an important role in quantifying NFs. It was also revealed that d ing and heterogeneity of materials contribute to the quantification of vibratory characteristics. The study provided important biomechanical insights and clinical references for future studies on dynamic behaviors of dental and periodontal structures.
Publisher: Springer Science and Business Media LLC
Date: 06-2003
Abstract: The fracture toughness of small volumes of brittle materials may be investigated by using pyramidal indenters to initiate radial cracks. The length of these cracks, together with indenting load and the hardness to modulus ratio of the material, were combined to calculate the critical stress intensity factor K c pertinent to fracture toughness. Modulus and hardness may be obtained from the literature or may be measured using nanoindentation techniques. If the material volume is very small, such as single grains in a conglomerate, a reduction of scale may be obtained by reducing the internal face angles of the indenter. This encourages crack initiation at lower loads, but cracks produced at very low loads are short and difficult to measure. Experiments on fused silica and glassy carbon suggested that radial cracks are initiated during loading and that when indenters with sufficiently small angles are used these cracks immediately pop-in, to become fully developed median/radial crack systems. Following pop-in, the rate of penetration of the indenter increases and at higher loads there is an extra increment of penetration over that which would otherwise have occurred. In this study a method is described whereby this extra penetration may be determined. Then for two dissimilar brittle materials, crack length is shown to be correlated with extra penetration leading to a relationship that may possibly avoid the necessity for crack-length measurement.
Publisher: Springer Science and Business Media LLC
Date: 06-1983
DOI: 10.1007/BF00723255
Publisher: Springer Science and Business Media LLC
Date: 03-1995
DOI: 10.1007/BF02307366
Publisher: Elsevier BV
Date: 12-2003
DOI: 10.1016/J.JOCA.2003.08.003
Abstract: To examine the effect of topical administration of glyceryl trinitrate (GTN), an exogenous nitric oxide (NO) donor, on the structural and biomechanical properties of uncalcified articular cartilage (UCC) in aged ewes. Twelve ewes were used for this study. Six of these were treated with 2% GTN ointment (0.7 mg/kg) twice per week (GTN), and the remaining six were used as normal controls (NOC). After sacrifice at 26 weeks, dynamic biomechanical indentation testing and thickness determination (by needle penetration) were performed on tibial plateau articular cartilage at 18 locations. Using histological sections prepared from the lateral and medial femoral condyles (LFC, MFC) and tibial plateau (LTP, MTP), the thickness of UCC, cartilage proteoglycan content (intensity of toluidine blue staining LFC, MFC only), and collagen birefringence (LTP, MTP, LFC only) were quantified by computer-assisted image analysis. Phase lag of tibial plateau cartilage was reduced in GTN sheep relative to NOC (mean of all testing locations 11.0+/-1.9 degrees vs 12.1+/-2.3 degrees P=0.0001). GTN treatment also globally reduced UCC thickness across the joint (ANOVA for all measured zones, P<0.0001). UCC thinning was most pronounced in the MFC (P=0.025) and LTP (P=0.0002). Proteoglycan content was reduced in the MFC(P=0.019), while collagen birefringence was increased in superficial cartilage zones of the LTP. NO donation via topical administration of GTN to normal ewes reduced the thickness and phase lag of femoro-tibial articular cartilage, suggesting a disturbance in chondrocyte metabolism. Regional alterations of collagen organisation and proteoglycan content were consistent with this interpretation.
Publisher: Elsevier BV
Date: 05-2008
DOI: 10.1016/J.ACTBIO.2007.11.002
Abstract: The aim of the study was to investigate the role of microstructure and porosity on the mechanical behaviour of sintered hydroxyapatite. Hydroxyapatite disks with four different porosities were used in this investigation. With a nanoindentation system, elastic modulus, hardness, contact stress-strain relationship, energy absorption and indentation creep behaviour were investigated. The elastic modulus and hardness of hydroxyapatite exhibited an exponential relationship (e(-bP)) with the porosity P, which is similar to Rice's finding with the minimum solid area model. High porosity s les showed more substantial inelastic behaviour, including higher energy absorption, no linear elastic region in the contact stress-strain curve and some indentation creep behaviour. We conclude that porous microstructure endows hydroxyapatite with inelastic deformation properties, which are important in a material for bone substitution usage.
Publisher: Springer Science and Business Media LLC
Date: 08-2006
Abstract: In the last decade, most publications on the mechanical properties of dental calcified tissues were based on nanoindentation investigation. This technique has allowed a better understanding of the mechanical behavior of enamel, dentin, and cementum at a nanoscale. The indentations are normally carried out using pointed or spherical indenters. Hardness and elastic modulus are measured as a function of indenter penetration depth and from the elastic recovery upon unloading. The unique microstructure of each calcified tissue significantly contributes to the variations in the mechanical properties measured. As complex hydrated biological composites, the relative proportions of the composite components, namely, inorganic material (hydroxyapatite), organic material, and water, determines the mechanical properties of the dental hard tissues. Many pathological conditions affecting dental hard tissues cause changes in mineral levels, crystalline structures, and mechanical properties that may be probed by nanoindentation. This review focuses on relevant nanoindentation techniques and their applications to enamel, dentin, and cementum investigations.
Publisher: Springer Science and Business Media LLC
Date: 05-1981
DOI: 10.1007/BF01033867
Publisher: Elsevier BV
Date: 12-1991
Publisher: Elsevier BV
Date: 04-2012
Publisher: Optica Publishing Group
Date: 19-08-2009
DOI: 10.1364/OE.17.015592
Publisher: Springer Science and Business Media LLC
Date: 1999
Abstract: Hydroxyapatite (HAp) coatings were deposited onto substrates of metal biomaterials (Ti, Ti6Al4V, and 316L stainless steel) by electrophoretic deposition (EPD). Only ultra-high surface area HAp powder, prepared by the metathesis method 10Ca(NO3)2 + 6(NH4)2HPO4 + 8NH4OH), could produce dense coatings when sintered at 875-1000degreesC. Single EPD coatings cracked during sintering owing to the 15-18% sintering shrinkage, but the HAp did not decompose. The use of dual coatings (coat, sinter, coat, sinter) resolved the cracking problem. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) inspection revealed that the second coating filled in the "valleys" in the cracks of the first coating. The interfacial shear strength of the dual coatings was found, by ASTM F1044-87, to be approximately 12 MPa on a titanium substrate and approximately 22 MPa on 316L stainless steel, comparing quite favorably with the 34 MPa benchmark (the shear strength of bovine cortical bone was found to be 34 MPa). Stainless steel gave the better result since -316L (20.5 microm mK(-1)) > alpha-HAp (approximately 14 microm mK(-1)), resulting in residual compressive stresses in the coating, whereas alpha-titanium (approximately 10.3 microm mK(-1)) < alpha-HAp, resulting in residual tensile stresses in the coating.
Publisher: Elsevier BV
Date: 02-2003
DOI: 10.1016/S0021-9290(02)00327-5
Abstract: This study investigates the nature of deformation and differences in the mechanisms of fracture and properties of dentine where there has been a loss of moisture, as may occur with removal of the pulp in the endodontic treatment of teeth. Controlled fracture toughness testing was conducted on bovine teeth to determine the influence of hydration on the work of fracture of dentine. Significant differences (p<0.01) were observed between the fracture toughness of hydrated (554+/-27.7J/m2) and dehydrated (113+/-17.8J/m2) dentine. Observations of the crack tip region during crack extension revealed extensive ligament formation occurred behind the crack tip. These ligaments provide considerable stability to the crack by significantly increasing the work of fracture, thereby acting as a fracture-toughening mechanism. Micro-cracking, reported as a fracture-toughening mechanism in bone, is also clearly seen. A zone of in-elastic deformation may occur as hydrated specimens revealed upon crack extension, a region about the tip that appeared to suck water into the structure and to exude water behind the crack tip. In dehydrated dentine, no in-elastic zone was observed. Micro-cracking is present though the cracks are smaller, straighter and with less opening than hydrated dentine. Only limited ligament formation just behind the crack tip was observed. These differences resulted in a significantly lower work of fracture with unstable brittle fracture characteristics. Based on these results, several fracture-toughening mechanisms were identified in dentine, with micro-cracking not considered the most important. These findings may be relevant for bone, a similar mineralised hydrated tissue.
Publisher: Elsevier BV
Date: 02-2003
Publisher: Elsevier BV
Date: 12-1995
Publisher: Wiley
Date: 28-11-2007
DOI: 10.1002/JBM.A.31051
Abstract: Enamel is a natural composite, which has much higher toughness than its major component, crystalline hydroxyapatite. In this study, the energy absorption behavior of human sound enamel was investigated with nanoindentation techniques. A UMIS nanoindenter system as well as a Berkovich and two spherical indenters with nominal tip radii of 5 and 20 microm were used to indent enamel at different loading forces in the direction parallel to enamel prisms. Inelastic energy dissipation versus depth of indenter penetration (U%-h(p) curve) as well as a function of indentation strain (U%-epsilon curve) of enamel was determined. Enamel showed much higher energy absorption capacity than a ceramic material with equivalent modulus (fused silica). Even at the lowest forces (1 mN) for the 20 microm indenter, inelastic response was found. Additional tests done at different force loading rates illustrated that load rate has little influence on P-h response of enamel. The top surface of enamel has the plastic work of indentation of approximately 5.2 nJ/microm(3). The energy absorbing ability is influenced by the very small protein rich component that exists between the hydroxyapatite nanocrystals as well as within the sheath structure surrounding the enamel rods.
Publisher: Wiley
Date: 26-12-2012
DOI: 10.1111/CLR.12106
Abstract: This qualitative study explored the perceptions of edentulous patients regarding their rehabilitation with maxillary and mandibular implant-supported overdentures employing a protocol that featured novel implant sites and distribution. In-depth semi-structured interviews were conducted with 16 participants who have taken part in a randomized controlled trial. Each received implant overdentures supported by either titanium or zirconia one-piece implants. Participants received four implants in the maxilla and three implants in the mandible. The implant distribution was: in the maxilla, a mid-palatal implant, and three anterior implants in the incisor and first premolar regions in the mandible, a mid-symphseal implant, and bilateral distal implants in the first molar region. All interviews were conducted by a researcher not involved with the clinical aspect of the randomized controlled trial and were transcribed verbatim and analyzed using a thematic inductive analysis approach. The perceived advantages of the treatment were functional improvement and increased social confidence. Cost was a significant barrier for edentulous patients seeking implant treatment. Previous experience with complete dentures, age and length of treatment was further factors that influenced decisions regarding prosthodontic rehabilitation. The novel implant protocol was acceptable to patients. Implant overdentures improve the quality of life of edentulous patients. Acceptance of dental implants may be increased by mitigating the cost of treatment. The mid-palatal implant site may be a potential alternative to extensive surgical procedures during the prosthodontic rehabilitation of atrophic maxillary ridges. The mandibular design offers patients the advantages of a removable prosthesis with increased retention.
Publisher: Wiley
Date: 26-05-2014
DOI: 10.1111/ADJ.12168
Abstract: The purpose of this study was to investigate the effect of fluoridated glass fillers on fluoride release, recharge and the flexural properties of modified polymethylmethacrylate (PMMA). Specimens of PMMA denture base material with various loading of fluoridated glass fillers (0%, 1%, 2.5%, 5% and 10% by weight) were prepared. Flexural properties were evaluated on rectangular specimens (n = 10) aged in deionized water after 24 hours, 1 and 3 months. Disc specimens (n = 10) were aged for 43 days in deionized water and lactic acid (pH 4.0) and fluoride release was measured at numerous intervals. After ageing, specimens were recharged and fluoride re-release was recorded at 1, 3 and 7 days after recharge. S les containing 2.5%, 5% and 10% glass fillers showed significantly (p < 0.05) greater levels of fluoride release compared with the control and 1% glass fillers specimens. All experimental specimens exhibited fluoride release in both media. The flexural strength of specimens decreased in proportion to the percentage filler inclusion with the modulus of elasticity values remaining within ISO Standard 1567. The modified PMMA with fluoridated glass fillers has the ability to release and re-release fluoride ion. Flexural strength decreased as glass filler uploading increased.
Publisher: Informa UK Limited
Date: 29-05-2016
DOI: 10.1080/10255842.2015.1028925
Abstract: Despite their considerable importance to biomechanics, there are no existing methods available to directly measure apparent Poisson's ratio and friction coefficient of oral mucosa. This study aimed to develop an inverse procedure to determine these two biomechanical parameters by utilizing in vivo experiment of contact pressure between partial denture and beneath mucosa through nonlinear finite element (FE) analysis and surrogate response surface (RS) modelling technique. First, the in vivo denture-mucosa contact pressure was measured by a tactile electronic sensing sheet. Second, a 3D FE model was constructed based on the patient CT images. Third, a range of apparent Poisson's ratios and the coefficients of friction from literature was considered as the design variables in a series of FE runs for constructing a RS surrogate model. Finally, the discrepancy between computed in silico and measured in vivo results was minimized to identify the best matching Poisson's ratio and coefficient of friction. The established non-invasive methodology was demonstrated effective to identify such biomechanical parameters of oral mucosa and can be potentially used for determining the biomaterial properties of other soft biological tissues.
Publisher: Oxford University Press (OUP)
Date: 17-03-2011
DOI: 10.1093/EJO/CJQ156
Abstract: The purpose of this study was to conduct a prospective randomized controlled clinical trial to evaluate the rate of space closure and tooth angulation during maxillary canine retraction using preactivated T-loops made from titanium-molybdenum alloy (TMA) and nickel-titanium (NiTi). Twelve patients (six males and six females) aged between 13 and 20 years who had upper premolar extractions were included, and each acted as their own control, with a NiTi T-loop allocated to one quadrant and TMA to the other using a split mouth block randomization design. The loops were activated 3 mm at each visit to deliver a load of approximately 150 g to the upper canine teeth. Maxillary dental casts, taken at the first and each subsequent monthly visit, were used to evaluate changes in extraction space and canine angulation. All used T-loops were compared with unused loops in order to assess distortion. Mixed model statistical analysis was used to adjust for confounding variables. The mean rate of canine retraction using preactivated NiTi and TMA T-loops was 0.91 mm/month (±0.46) and 0.87 mm/month (±0.34), respectively. The canine tipping rates were 0.71 degrees/month (±2.34) for NiTi and 1.15 degrees/month (±2.86) for TMA. Both the rate of space closure and the tipping were not significantly different between the two wire types. The average percentage distortion of the TMA T-loop was 10 times greater than that of the NiTi loops when all other variables were matched. There was no difference in the rate of space closure or tooth angulation between preactivated TMA or NiTi T-loops when used to retract upper canines. The NiTi loops possessed a greater ability to retain and return to their original shapes following cyclical activation.
Publisher: Wiley
Date: 28-05-2013
DOI: 10.1111/ADJ.12040
Abstract: In the previous three papers, the authors sought to conduct a thorough analysis of the feasibility for the use of zirconia in inlay supported, fixed partial dentures via finite element analysis (FEA). Correlating the response of the numerical model against the experimental model has never been satisfactorily performed for an anatomically accurate ceramic bridge such validation is crucial if the results from the FEA are to be confidently relied upon. Part 4 of this series is a detailed fractographic analysis of the zirconia bridge that was the model for the experimental validation, performed in order to confirm the fracture origin/s and fracture trajectory as predicted from the FEA. Established fractographic techniques involving optical examination followed by examination with scanning electron microscopy were conducted. The porous, granular surface of zirconia (both partially and fully sintered) does not lend itself to easy surface analysis but the classic fractographic signs (hackle lines, wake hackle lines and compression curl) are present. Use of linear fracture elastic mechanics allowed the calculation of theoretical critical flaw size and a comparison to two defects or inclusions found at the primary origin of fracture. Excellent agreement between the fracture sites and paths of travel as predicted in the numerical analysis exist with fractographic analysis. Furthermore, the calculated critical flaw size of 30 μm to 40 μm equates very well with defects seen at the general vicinity of the primary fracture origin and the general observed size of critical flaws in machined ceramics which range between 20 μm to 50 μm, thus providing further confirmation. The fractographic analysis detailed in this study provides validation of the 'zones of failure' as predicted in our FEA. Additionally, the excellent correlation between the calculated critical flaw size and the defects observed at the primary fracture site demonstrates that field of experimental mechanics is a powerful predictive tool.
Publisher: Elsevier BV
Date: 02-2010
DOI: 10.1016/J.DENTAL.2009.12.002
Abstract: The goal of this paper is to undertake a literature search collecting all dentin bond strength data obtained for six adhesives with four tests (shear, microshear, tensile and microtensile) and to critically analyze the results with respect to average bond strength, coefficient of variation, mode of failure and product ranking. A PubMed search was carried out for the years between 1998 and 2009 identifying publications on bond strength measurements of resin composite to dentin using four tests: shear, tensile, microshear and microtensile. The six adhesive resins were selected covering three step systems (OptiBond FL, Scotch Bond Multi-Purpose Plus), two-step (Prime & Bond NT, Single Bond, Clearfil SE Bond) and one step (Adper Prompt L Pop). Pooling results from 147 references showed an ongoing high scatter in the bond strength data regardless which adhesive and which bond test was used. Coefficients of variation remained high (20-50%) even with the microbond test. The reported modes of failure for all tests still included high number of cohesive failures. The ranking seemed to be dependant on the test used. The scatter in dentin bond strength data remains regardless which test is used confirming Finite Element Analysis predicting non-uniform stress distributions due to a number of geometrical, loading, material properties and specimens preparation variables. This reopens the question whether, an interfacial fracture mechanics approach to analyze the dentin-adhesive bond is not more appropriate for obtaining better agreement among dentin bond related papers.
Publisher: Elsevier BV
Date: 2010
DOI: 10.1016/J.JDENT.2010.08.016
Abstract: The aim of this study is to compare the influence of the opaque application method on the adhesion and final shade of porcelain-fused-to-metal restorations. Four s les (n=12) were cast in a NiCrMo alloy and opaqued using three application methods: aerosol-spray (one application), aerosol-spray (two applications), paste and powder-liquid prior to veneering with dentine porcelain to a thickness of 1.0mm to mimic the clinical thickness of porcelain-fused-to-metal crowns. The porcelain to metal adhesion was determined by measuring the interfacial fracture toughness or strain energy release rate with a four-point bending configuration developed by Charalambides et al.,(13) at a loading rate of 0.05mm min(-1) in kerosene. The resultant porcelain shade was measured with a spectrophotometer under daylight. Values of L*, a* and b* were used to calculate the total color difference ΔE with different equations CIELAB, CMC(1:1), CIE94, and CIEDE2000. The resulting values were also compared with a reference unbonded s le made from the same dentine porcelain used to veneer the porcelain-fused-to-metal specimens. The application technique of the opaque did not influence the adhesion between the porcelain and metal. All the application methods demonstrated brittle cracking behaviour through the opaque layer. No visible color differences were found between the applications methods in the final shade of the porcelain. The application method in terms of bond strength and final porcelain shade is not a factor in choosing which method to use in the dental laboratory.
Publisher: Wiley
Date: 02-0011
Publisher: Informa UK Limited
Date: 11-2017
Publisher: Elsevier BV
Date: 10-2018
DOI: 10.1016/J.JSB.2018.06.006
Abstract: Proteins of the inter-rod sheath and peptides within the narrow inter-crystallite space of the rod structure are considered largely responsible for visco-elastic and visco-plastic properties of enamel. The present study was designed to investigate putative peptides of the inter-crystallite space. Entities of 1-6 kDa extracted from enamel rods of erupted permanent teeth were analysed by mass spectrometry (MS) and shown to comprise N-terminal amelogenin (AMEL) peptides either containing or not containing exon 4 product. Other dominant entities consisted of an N-terminal peptide from ameloblastin (AMBN) and a series of the most hydrophobic peptides from serum albumin (ALBN). Amelogenin peptides encoded by the Y-chromosome allele were strongly detected in Enamel from male teeth. Location of N-terminal AMEL peptides as well as AMBN and ALBN, between apatite crystallites, was disclosed by immunogold scanning electron microscopy (SEM). Density plots confirmed the relative abundance of these products including exon 4+ AMEL peptides that have greater capacity for binding to hydroxyapatite. Hydrophilic X and Y peptides encoded in exon 4 differ only in substitution of non-polar isoleucine in Y for polar threonine in X with reduced disruption of the hydrophobic N-terminal structure in the Y form. Despite similarity of X and Y alleles of AMEL the non-coding region upstream from exon 4 shows significant variation with implications for segregation of processing of transcripts from exon 4. Detection of fragments from multiple additional proteins including keratins (KER), fetuin A (FETUA), proteinases and proteinase inhibitors, likely reflect biochemical events during enamel formation.
Publisher: Elsevier BV
Date: 12-2008
DOI: 10.1016/J.JBIOMECH.2008.09.018
Abstract: The biomechanical stability of osseointegrated implants is of particular importance, especially the stability which is achieved from structural manipulation at the interface between the implant surface and the bone tissues. Nanoscale beta-tricalcium phosphate-immobilized titanium was prepared by discharge into a physiological buffered saline solution. Compared with hydroxyapatite, it has been shown to be effective in generating a bone-like chemical structure on the surface by cooperative interaction between osteoblastic cells and the beta-tricalcium phosphate. The present study, after cell cultivation, investigates the nanostructures and biomechanical property differences of a mineralized layer formed on two s les of nano-calcium phosphate-immobilized titanium. A scanning probe microscope study revealed that the mineralized tissue formed on the beta-tricalcium phosphate s les after 1 week of cell culture showed significantly higher roughness, compared with hydroxyapatite s les. Nanoindentation micromechanical evaluation of the in vitro generated multilayered structures exhibited thicker bone-like mineralized layers on the beta-tricalcium phosphate s les. A successful modification of titanium implants through the cooperative interaction between osteoblastic cells and nano beta-tricalcium phosphate is anticipated.
Publisher: Wiley
Date: 03-2018
DOI: 10.1111/ANZS.12209
Publisher: The Royal Society
Date: 28-03-2015
Abstract: Tooth enamel has the critical role of enabling the mastication of food and also of protecting the underlying vital dentin and pulp structure. Unlike most vital tissue, enamel has no ability to repair or remodel and as such has had to develop robust damage tolerance to withstand contact fatigue events throughout the lifetime of a species. To achieve such behaviour, enamel has evolved a complex hierarchical structure that varies slightly between different species. The major component of enamel is apatite in the form of crystallite fibres with a nanometre-sized diameter that extend from the dentin–enamel junction to the oral surface. These crystallites are bound together by proteins and peptides into a range of hierarchical structures from micrometre diameter prisms to 50–100 μm diameter bundles of prisms known as Hunter–Schreger bands. As a consequence of such complex structural organization, the damage tolerance of enamel increases through various toughening mechanisms in the hierarchy but at the expense of fracture strength. This review critically evaluates the role of hierarchy on the development of the R-curve and the stress–strain behaviour. It attempts to identify and quantify the multiple mechanisms responsible for this behaviour as well as their impact on damage tolerance.
Publisher: Wiley
Date: 02-1983
Publisher: IOP Publishing
Date: 30-10-2008
DOI: 10.1088/0957-4484/19/47/475709
Abstract: We investigate the mechanical response of 50-600 nm epitaxial Ge films on a Si substrate using nanoindentation with a nominally spherical (R≈4.3 µm) diamond tip. The inelastic deformation mechanism is found to depend critically on the film thickness. Sub-100 nm Ge films deform by pressure-induced phase transformation, whereas thicker films deform only by shear-induced dislocation slip and twinning. Nanoindentation fracture response is similarly dependent on film thickness. Elastic stress modelling shows that differing stress modes vary in their spatial distribution, and consequently the film thickness governs the stress state in the film, in conjunction with the radius of the nanoindenter tip. This opens the prospect of tailoring the contact response of Ge and related materials in thin film form by varying film thickness and indenter radius.
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.DENTAL.2011.08.005
Abstract: To evaluate the influence of occlusal geometry of all-ceramic pre-molars, namely cusp angle and associated notch radius, on the scatter of load to failure tests. Forty-five all-ceramic upper pre-molar crowns with three zirconia core thicknesses (0.4, 0.6 and 0.8 mm) were broken on dental implant abutments oriented in three angulations (0°, 15°, and 30°). The crowns were loaded using a 4 mm diameter steel cylindrical bar placed along the midline fissure at a crosshead speed of 1 mm min(-1). The scatter of the failure load was evaluated using Weibull analysis. The cusp angle of each crown was critically evaluated to determine the cusp angle and effective radius of the fissure notch root. The relationship between failure load and cusp angle was compared with that between failure load and effective radius as well as notch induced stress concentration by considering R(2) values of fitted trend lines with these relationships. The fracture load differences either between abutment angulations or zirconia thicknesses were not clearly revealed in this study. Except for the group of 30° abutment angulation, the crowns present high scatter of failure loads with low Weibull modulus. However, a simple dependence between fracture load and effective cusp angle was observed. Occlusal geometry is an important issue that affects the degree of stress concentration and should be understood by both technician and clinician for appropriate design and material selection of all-ceramic crowns.
Publisher: Elsevier BV
Date: 12-2011
DOI: 10.1016/J.DENTAL.2011.08.002
Abstract: This study evaluated the effect of different chemical surface treatments on the surface characteristics of commercially pure titanium (cp Ti) and the adhesion of the porcelain-titanium system by means of strain energy release rate (G-value, J/m(2)). Surface roughness and morphology of treated cp Ti were additionally evaluated. Two hundred and thirty specimens of machined cp Ti plates grade II were prepared. The specimens were ided into ten groups in each test according to the surface treatment used Gr 1 (control machined), Gr 2 (sandblasted), Gr 3 (CH(2)Cl(2) for 5 min), Gr 4 (CH(2)Cl(2) for 10 min), Gr 5 (10% H(2)O(2) for 5 min), Gr 6 (10% H(2)O(2) for 10 min), Gr 7 (30% H(2)O(2) for 5 min), Gr 8 (30% H(2)O(2) for 10 min), Gr 9 (9% HF for 5 min) and Gr 10 (9% HF for 10 min). Titanium-porcelain (Vita Titankeramik) was applied to each group for testing the adhesion. The G-value (J/m(2)) was measured with a four-point bending configuration. Following fracture testing specimens were examined with a scanning electron microscope (SEM). Surface roughness and SEM analysis were carried out. Data were analyzed using ANOVA and Tukey's test. Groups treated with 9% HF or CH(2)Cl(2) baths for 10 or 5 min showed the highest adhesion values (J/m(2)) (34.23±4.31, 30.75±4.91, 28.92±4.33 and 22.54±3.58) respectively among the groups. The machined groups demonstrated the lowest value (8.18±1.95) (J/m(2)). SEM analysis indicated a combination of cohesive and adhesive fractures for 9% HF, CH(2)Cl(2), sandblasted and 30% H(2)O(2) (10 min) groups, while mainly adhesive fractures were found with the other groups. There was no direct correlation between surface roughness and adhesion. Adhesion between porcelain and cp Ti can be improved by the use of certain chemical surface treatments prior to porcelain firing as alternative techniques to sandblasting treatment.
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.DENTAL.2011.08.003
Abstract: The aim of this study was to evaluate the fracture toughness and surface residual stresses present in various pressable ceramics to zirconia resulting from cooling induced temperature gradients. Indentation fracture toughness was used to evaluate the residual stress present in various pressable ceramics (Noritake CZR Press, Vita PM9, Wieland PressXzr and IPS e.max ZirPress) to zirconia when subjected to different cooling regimen. The cooling responses of two ceramics were evaluated by thermocouples embedded in the surface of the porcelains and at the porcelain-zirconia interface. The effective K(c) results obtained by indentation tests confirmed the presence of surface residual compressive stress for all-ceramic systems subjected to different cooling procedures. The residual stresses were quantified from the change in the radial crack size and the values compared for each ceramic before pressing, pressed ceramic only and pressed ceramic veneered on zirconia, from fast to slow cooling rates. A significant level of residual stress was found in the materials before pressing. Slow cooling significantly reduced the formation of residual stress for all pressed ceramics. From data produced by the thermocouples it was found that 'slow cooling' generated the least temperature difference between inner and outer surfaces of porcelain. A direct relationship was found for the cooling induced temperature difference between the surfaces, and interface thermocouples, and magnitude of the surface residual stresses. Leucite containing porcelains have higher intrinsic fracture toughness, and for all porcelains fast cooling generated significant residual stress within the veneering porcelain. To reduce development of residual stress, slow cool is recommended on the last heating cycle (e.g. glazing cycle).
Publisher: IOP Publishing
Date: 23-06-2009
Publisher: Springer Science and Business Media LLC
Date: 1991
DOI: 10.1007/BF01295614
Publisher: MDPI AG
Date: 05-03-2015
DOI: 10.3390/MA8030932
Publisher: Elsevier BV
Date: 12-2011
DOI: 10.1016/J.DENTAL.2011.08.006
Abstract: To compare the crystalline phases present, quantify the adhesion to zirconia and measure the mechanical properties of four commercially available pressed ceramics suitable for zirconia substructures. This study compares the X-ray diffraction response and the mechanical properties of four different pressed ceramics (Noritake CZR Press, Vita PM9, Wieland PressXzr and IPS e.max ZirPress) to Vita In-Ceram YZ zirconia substrate. The adhesion was determined using the interfacial strain energy release rate fracture mechanics approach in addition biaxial flexural strength values of each material was determined. X-ray diffraction analysis revealed that Noritake CZR Press and Vita PM9 contain leucite whereas IPS e.max ZirPress and Wieland PressXzr are non-leucite amorphous materials. The strain energy release rate results revealed that the pressed ceramics with leucite have better adhesion than non-leucite ceramics to zirconia. Differences were observed between biaxial strength results for the pressed ceramics from bilayer compared with monolayer specimens. Pressed ceramics compatible with zirconia tested in this study were of two types leucite containing and non-leucite containing essentially glass ceramics. Leucite containing pressable ceramics appears to have better adhesion to zirconia.
Publisher: IEEE
Date: 10-2015
Publisher: Elsevier BV
Date: 2014
DOI: 10.1016/J.JMBBM.2013.09.024
Abstract: Ballistic gelatin is frequently used as a model for soft biological tissues that experience projectile impact. In this paper we investigate the response of a number of gelatin materials to the penetration of spherical steel projectiles (7 to 11mm diameter) with a range of lower impacting velocities (<120m/s). The results of sphere penetration depth versus projectile velocity are found to be linear for all systems above a certain threshold velocity required for initiating penetration. The data for a specific material impacted with different diameter spheres were able to be condensed to a single curve when the penetration depth was normalised by the projectile diameter. When the results are compared with a number of predictive relationships available in the literature, it is found that over the range of projectiles and compositions used, the results fit a simple relationship that takes into account the projectile diameter, the threshold velocity for penetration into the gelatin and a value of the shear modulus of the gelatin estimated from the threshold velocity for penetration. The normalised depth is found to fit the elastic Froude number when this is modified to allow for a threshold impact velocity. The normalised penetration data are found to best fit this modified elastic Froude number with a slope of 1/2 instead of 1/3 as suggested by Akers and Belmonte (2006). Possible explanations for this difference are discussed.
Publisher: Informa UK Limited
Date: 12-2001
Publisher: Elsevier BV
Date: 08-1998
Publisher: The Angle Orthodontist (EH Angle Education & Research Foundation)
Date: 11-2008
DOI: 10.2319/092707-460.1
Abstract: Objective: To test the null hypothesis that temperature has no effect on the force, moment, and moment to force ratio (M:F) of nickel-titanium (NiTi) and titanium molybdenum alloy (TMA) T-loops. Materials and Methods: Twelve symmetrical T-loops were constructed from NiTi and TMA rectangular wires (N = 24). For each material, four specimens had 30° preactivation bent into the legs, four had 15°, and the remainder no preactivation. The specimens were mounted on a custom stand incorporating a force and a moment transducer housed in an insulated oven in which the temperature was varied from 10°C to 50°C in 10° increments (±0.5°C). The loops were opened in 1-mm increments to a maximum of 8 mm and allowed to return to the rest position. Forces and moments were recorded at each interval from this, the M:F was calculated. Mixed-model statistical analysis was used to detect differences between mean results of material type, preactivation, and temperature. Results: Temperature significantly influenced the forces and moments (P & .000) produced by NiTi closing loops, with values increasing as the temperature increased. The M:F ratios of NiTi loops were less affected, with no significant changes with temperature for the 15° and 30° preactivation loops, although some change was noted for the non-preactivated loops. TMA wires showed significance for some force measurements, but were generally not influenced by temperature. Conclusion: The hypothesis is rejected. Temperature significantly affected the forces and moments produced by NiTi T-loops, though these changes generally do not affect the overall M:F ratio.
Publisher: Elsevier BV
Date: 09-2008
DOI: 10.1016/J.MEDENGPHY.2007.09.008
Abstract: Bisphosphonates are commonly used for the treatment of osteoporosis and have recently been shown to increase bone mineral parameters and strength in endochondral fracture repair. There is concern, however, that BPs may negatively affect bone material properties. Nanoindentation was performed on femoral fracture s les of rats that had undergone closed fracture healing for six weeks to determine hardness and elastic modulus. The rats had received either intravenous saline or a single intravenous dose of zoledronic acid at zero, one or two weeks post fracture (n = 3 per group). The mean elastic modulus and hardness of mineralised tissue in control calluses were mean 16.4 GPa (S.D. 2.3) and mean 0.65 GPa(S.D. 0.1), respectively. There was no significant change in these parameters with zoledronic acid treatment. The results from this preliminary data suggest that single dose zoledronic acid treatment in fracture healing may not adversely affect the intrinsic properties of callus bone tissue. Single dose bisphosphonate may be a viable treatment for augmenting fracture repair without negatively affecting the material properties.
Publisher: Elsevier BV
Date: 12-2016
Publisher: Wiley
Date: 04-04-2007
DOI: 10.1002/JBM.B.30784
Publisher: Wiley
Date: 29-05-2013
DOI: 10.1111/JMI.12053
Abstract: Human tooth is a complex bioceramic composite, which consists of enamel, dentin and the interface, the dentin-enamel junction (DEJ). The crystal properties and ultrastructure of the inorganic phase through the thickness of healthy human molar teeth were investigated using X-ray microdiffraction (μXRD), electron diffraction and transmission electron microscopy (TEM) techniques. The XRD data were analysed using the Le Bail profile fitting approach. The size and the texture of the crystallites forming enamel and dentin in the crown part of teeth were measured using both techniques and then compared. Results showed that the thickness of dentin crystallites was found to decrease towards the DEJ, whereas the thickness of the enamel crystallites increased from the DEJ towards the outer layers. It was demonstrated that enamel exhibited an increase of texture in 002 lattice planes from the DEJ towards the outer layers. Texture was also detected in 102 lattice planes. The texture effect in 002 planes at the scale of less than 1 μm was also demonstrated in dentin. The variation of lattice parameters as a function of the position within the thickness of dentin and enamel was also observed. The values of the nonuniform microstrain in the dentin and enamel crystallites were from 1.40 × 10(-6) % to 4.44 × 10(-5) %. The good correlation between XRD and TEM indicated that μXRD is a useful technique to study crystallography and microstructure of heterogeneous enamel and dentin. The observed gradient characteristics of texture and crystallite size in enamel and dentin maybe an evolutionary outcome to resist wear and fracture, thereby contributing to the excellent mechanical properties of teeth.
Publisher: Elsevier BV
Date: 1978
Publisher: Springer Science and Business Media LLC
Date: 06-1999
Abstract: Details of microindentation of silicon, such as the semiconductor-to-metal transformation, which takes place on loading, have been examined using spherical indenters. Various forms of silicon are studied, including heavily boron-doped wafers and silicon damaged and amorphized by ion implantation as well as material containing dislocations. Results indicate that only silicon, which contains high concentrations of point defects or is amorphous, exhibits mechanical properties that differ significantly from undoped, defect-free crystal. Amorphous silicon exhibits plastic flow under low indentation pressures and does not appear to undergo phase transformation on loading and unloading. Indentation of compound semiconductors is also studied and the load/unload behavior at room temperature is quite different from that of silicon. Both gallium arsenide and indium phosphide, for ex le, undergo slip-induced plasticity above a critical load.
Publisher: No publisher found
Date: 1995
DOI: 10.1007/BF01184600
Publisher: Wiley
Date: 03-1986
Publisher: Elsevier BV
Date: 12-1975
Publisher: American Physical Society (APS)
Date: 28-02-2003
Publisher: Elsevier BV
Date: 05-2000
Publisher: Elsevier BV
Date: 04-2009
DOI: 10.1016/J.JDENT.2008.11.020
Abstract: To compare the demineralization pattern that occurs in abraded s les and unabraded ones quantitatively and microscopically using nanoindentation and SEM. Using 12 human third molars, one half of each tooth was abraded to a depth approximately 200 microm below the outer surface enamel, and the other half was left untreated. All specimens were demineralized for 3d, 5d, 7d and 14d respectively. The cross sections of all lesions were evaluated with nanoindentation and SEM. Unabraded s les had least loss of mechanical properties and lesion depth compared to abraded s les, with most mechanical property loss occurring within a shallower layer of the lesion. The variation of mechanical properties in unabraded s les was wider than abraded s les. SEM images showed a characteristic "keyhole" structure for both s les after demineralization, with the rod core extensively demineralized while the interrod remained intact. Acid attack initiated at the rod sheath space then penetrated into the rod core before extending into neighbouring rods through the rod tail. Abraded s les exposed to in vitro demineralization form deeper lesion depths and greater loss of mechanical properties than unabraded s les subjected to the same demineralization. Unabraded s les manifested characteristic subsurface demineralization with a shallow surface layer that remained intact, whereas no intact surface was found in abraded s les. The demineralization pattern of unabraded s les more closely resembled the pattern of natural white spot lesions and displayed wide inter-s le variation. Consideration should be given to experimental design with unabraded teeth specimens for future demineralization studies.
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.DENTAL.2011.08.001
Abstract: The occurrence of "chipping" of all-ceramic restorations with Y-TZP frameworks has resulted in various designs and cooling procedures recommended for reducing such behavior. In this paper the temperature gradients during fast and slow cooling for conventional and anatomical designs are compared as well as an optical procedure to directly compare the influence of cooling rate on residual stress. This investigation quantifies the temperature gradients between the inner and outer surfaces of crowns measured with thermocouples during two different cooling methods with uniform and anatomical frameworks. In the first method the crown was removed from the furnace after commencement of cooling whereas for the second method the crown was cooled to the glass transition temperature (600°C) before removal. Direct observation of the residual stresses was made with an optical polarimeter and thin slices of veneered copings. This study observed that slow cooling decreases the temperature differences but still differences of up to 88°C were observed. For the fast cooled crown, temperature differences of more than 100°C for the uniform and 140°C for the anatomical framework at temperatures above the glass transition temperature were recorded. Optical polarimeter observations indicated much lower stresses within the porcelain layer upon cooling by removing the crown below the glass transition temperature. Slow cooling during the final veneering of dental restorations with zirconia frameworks reduces the temperature gradients and residual stresses within the porcelain layer, which represent one possible cause for chipping. An anatomical designed framework did not show the same reduction extent.
Publisher: No publisher found
Date: 2013
Abstract: The databases Medline/PubMed, EMBASE, the Cochrane Library, Chinese Biomedical Literature Database and the China National Knowledge Infrastructure were searched. Additional hand searches were conducted in the journals. Randomised controlled trials, prospective cohort studies and retrospective studies with follow-up of 36 months or longer were included. Data were extracted independently in duplicate. The annual core and veneer fracture rates of various tooth types were estimated and compared using Poisson regression. 37 studies were included two RCTs, 25 prospective cohorts and 10 retrospective studies. Based on the calculated results, all-ceramic crowns had an acceptable overall five-year fracture rate of 4.4% irrespective of the materials used. Five-year fracture rates were significantly higher for molar crowns (8.1%) compared to premolar crowns (3.0%), and the difference between anterior (3.0%) and posterior crowns (5.4%) also achieved significance. Core fracture rates had a five-year incidence of 2.5%, and a significantly higher core fracture rate was found in the posterior region (3.9%). The overall five-year incidence of veneer fracture was 3.0%, and no clear difference was found between restored tooth types, with incidences of 2.0%, 2.5%, 1.0%, and 3.0% for incisor, canine, premolar, and molar crowns, respectively. Within the limitations of this study's protocol, the current evidence suggests that dental ceramic materials demonstrated acceptable five-year core and veneer fracture incidences when used for tooth-supported single crowns in both anterior and posterior segments. Higher fracture tendency for posterior crowns was the trend for all-ceramic crowns, while molar crowns showed a significantly higher fracture rate than premolar crowns. Randomised controlled trials with large s le sizes be undertaken to obtain more definitive results.
Publisher: Elsevier BV
Date: 11-2008
DOI: 10.1016/J.DENTAL.2008.03.021
Abstract: The aim of the study is to investigate the visco-elastic response of an alginate irreversible hydrocolloid dental impression material during setting. A novel squeeze film Micro-Fourier Rheometer (MFR, GBC Scientific Equipment, Australia) was used to determine the complex modulus of an alginate irreversible hydrocolloid dental impression material (Algident, ISO 1563 Class A Type 1, Dentalfarm Australia Pty. Ltd.) during setting after mixing. Data was collected every 30s for 10 min in one study and every 10 min for a total of 60 min in another study. A high level of repeatability was observed. The results indicate that the MFR is capable of recording the complex shear modulus of alginate irreversible hydrocolloid for 60 min from the start of mixing and to simultaneously report the changing visco-elastic parameters at all frequencies between 1 Hz and 100 Hz. The storage modulus shows a dramatic increase to 370% of its starting value after 6 min and then reduces to 55% after 60 min. The loss modulus increases to a maximum of 175% of its starting value after 10 min and then reduces to 94% after 60 min. The MFR enables the changes in the complex modulus through the complete setting process to be followed. It is anticipated this approach may provide a better method to compare the visco-elastic properties of impression materials and assist with identification of optimum types for different clinical requirements. The high stiffness of the instrument and the use of band-limited pseudo-random noise as the input signal are the main advantages of this technique over conventional rheometers for determining the changes in alginate visco-elasticity.
Publisher: Wiley
Date: 11-1982
Publisher: Springer Science and Business Media LLC
Date: 1978
DOI: 10.1007/BF00876542
Publisher: Elsevier BV
Date: 05-1980
Publisher: Portico
Date: 2010
DOI: 10.4061/2010/902537
Publisher: Elsevier BV
Date: 12-1997
DOI: 10.1016/S0142-9612(97)80007-5
Abstract: An attempt has been made to measure the critical strain energy release rate or interfacial toughness between an oxide coating and metal layer in the present study. Twelve pure titanium cast plates veneered with transparent incisal porcelain were subjected to four-point bending after introducing a precrack through a controlled notch on the ceramic veneer. Cycles of loading and unloading at crosshead speed of 0.1 mm min-1 were repeated and extension of the crack along the interfacial oxide layer was observed through the transparent porcelain. Parallelled extension with the initial notch at each loading was observed and multiple loading was possible until the crack reached the inner loading points. Fracture resistance was calculated by iding the energy value determined from a force-displacement curve by the corresponding fracture area. A theoretical calculation of the fracture resistance using a formula developed by Charalambides et al. (J. Appl. Mech., 1989, 56, 77-82) was also estimated. The result from the two methods agreed well (R2 = 0.75) but the theoretical calculation (16.06 +/- 4.53J m2) gave lower average value than the other value (18.29 +/- 4.23J m2), (p < 0.05). These preliminary results indicate that this novel technique is a suitable means for quantifying interfacial toughness of porcelain-metallic bonding.
Publisher: Wiley
Date: 03-1986
Publisher: Elsevier BV
Date: 05-1999
Publisher: SAGE Publications
Date: 06-2009
Abstract: Tooth enamel is the hardest tissue in the human body and is directly responsible for dental function. Due to its non-regenerative nature, enamel is unable to heal and repair itself biologically after damage. We hypothesized that with its unique microstructure, enamel possesses excellent resistance to contact-induced damage, regardless of loading direction. By combining instrumented indentation tests with microstructural analysis, we report that enamel can absorb indentation energy through shear deformation within its protein layers between apatite crystallites. Moreover, a near-isotropic inelastic response was observed when we analyzed indentation data in directions either perpendicular or parallel to the path of enamel prisms. An “effective” crystal orientation angle, 33°–34°, was derived for enamel microstructure, independent of the loading direction. These findings will help guide the design of the nanostructural architecture of dental restorative materials.
Publisher: Elsevier BV
Date: 2015
DOI: 10.1016/J.ACTBIO.2014.09.009
Abstract: The combined effect of alumina and silica co-doping on the ageing resistance of 3Y-TZP bioceramics was investigated. In order to differentiate between the distinct contributions of two dopants to the overall resistance to low-temperature degradation (LTD), specimens were prepared by infiltration of silica sol into pre-sintered 3Y-TZP pellets, produced from commercially available powders, which were alumina-free or contained 0.05 and 0.25 wt.%. After sintering, specimens were exposed to accelerated ageing in distilled water at 134°C for 6-48 h. X-ray diffraction was applied to quantify the tetragonal-to-monoclinic (t-m) phase transformation associated with the LTD, while a focused ion beam-scanning electron microscopy technique was employed to study the microstructural features in the transformed layer. The results showed that the minor alumina and/or silica additions did not drastically change the densities, grain sizes or mechanical properties of 3Y-TZP, but they did significantly reduce LTD. The addition of either alumina or silica has the potential to influence both the nucleation and the propagation of moisture-induced transformation, but in different ways and to different extents. The co-doped ceramics exhibited predominantly transgranular fracture, reflecting strong grain boundaries (limiting microcracking of the transformed layer), for alumina doping, and rounded grains with a glassy phase at multiple grain junctions (reducing internal stresses) for silica-doped material. These two additives evidently have different dominant mechanisms associated with the deceleration of LTD of 3Y-TZP, but their combination increases resistance to ageing, importantly, without reducing the fracture toughness of this popular biomaterial.
Publisher: Elsevier BV
Date: 2014
DOI: 10.1016/J.DENTAL.2013.08.199
Abstract: In this brief and selective overview, basic factors contributing to aqueous induced dissolution, phase changes of zirconia and mechanical strength degradation of dental ceramics are considered. Dissolution is important for porcelain and glass-ceramic materials as they predominantly contain a silica glass structure with various other cations incorporated which disrupt the silica network. In glass-ceramic materials and porcelains containing crystalline components the situation is more complex as the difference in the dissolution rate may increase the surface roughness and contribute to abrasion of the opposing definition. Factors contributing to the aqueous dissolution of silicate based dental ceramics and induced destabilization of Y-TZP zirconia or low temperature degradation (LTD) are considered. It is also noted that there have been a number of reports of spontaneous fracture of 3Y-TZP specimens because of LTD in the absence of external stress. A simple analysis of this situation is presented which indicates a strong specimen-size effect and also implicates the role of the remnant "pseudo-grain" structure resulting from the pressing of spray-dried powder agglomerates. The final section of this review addresses the consequences of various environments on crack growth and strength degradation. In some situations it is suggested that the aqueous environment may enhance the strength of restorative materials. In all instances discussed above the clinical consequences are pointed out.
Publisher: Elsevier BV
Date: 09-2008
DOI: 10.1016/J.ACTBIO.2008.04.010
Abstract: The aim of the present study was to investigate the ultrastructural mechanisms involved in the formation of caries-induced intratubular dentine. Conventional, high resolution and scanning transmission electron microscopy, electron diffraction and energy-dispersive X-ray spectroscopy techniques were used to study the ultrastructure of the inorganic phase in the transparent zone of carious dentine. The results demonstrated that the bulk of the inorganic phase in caries-induced intratubular dentine had an apatite crystal structure with the presence of additional Mg-substituted beta-TCP (beta-tricalcium phosphate) phase in the carious region. Highly oriented apatite crystallites observed in intratubular dentine demonstrated a regulated biomineralization process during the formation of inorganic phase in this region, whereas Mg beta-TCP crystals were presumably formed purely via "dissolution recipitation" mechanism. The study demonstrated the importance of "dissolution recipitation" process and the growth kinetics of Mg-substituted beta-TCP crystals in understanding the process of formation of calcium-phosphate crystallites in carious intratubular dentine.
Publisher: Elsevier BV
Date: 09-2004
Publisher: Elsevier BV
Date: 1987
Publisher: Wiley
Date: 19-11-2009
DOI: 10.1002/JBM.B.31531
Abstract: Functionally graded material (FGM) had been developed as a potential implant material to replace titanium for its improved capability of initial osseointegration. The idea behind FGM dental implant is that its properties can be tailored in accordance with the biomechanical needs at different regions adapting to its hosting bony tissues, therefore creating an improved overall integration and stability in the entire restoration. However, there have been very few reports available so far on predicting bone remodeling induced by FGM dental implants. This article aims to evaluate bone remodeling when replacing the titanium with a hydroxyapatite/collagen (HAP/Col) FGM model. A finite element model was constructed in the buccal-lingual section of a dental implant-bone structure generated from in vivo CT scan images. The remodeling simulation was performed over a 4 year healing period. Comparisons were made between the titanium implant and various FGM implants of this model. The FGM implants showed an improved bone remodeling outcome. The study is expected to provide a basis for future development of FGM implants.
Publisher: Springer Science and Business Media LLC
Date: 26-04-2008
DOI: 10.1007/S10856-008-3441-2
Abstract: Molar-incisor-hypomineralisation (MIH), one of the major developmental defects in dental enamel, is presenting challenge to clinicians due, in part, to the limited understanding of microstructural changes in affected teeth. Difficulties in the preparation of site-specific transmission electron microscope (TEM) specimens are partly responsible for this deficit. In this study, a dual-beam field emission scanning electron microscope (FESEM)/focused ion beam (FIB) milling instrument was used to prepare electron transparent specimens of sound and hypomineralised enamel. Microstructural analysis revealed that the hypomineralised areas in enamel were associated with marked changes in microstructure loosely packed apatite crystals within prisms and wider sheath regions were identified. Microstructural changes appear to occur during enamel maturation and may be responsible for the dramatic reduction in mechanical properties of the affected regions. An enhanced knowledge of the degradation of structural integrity in hypomineralised enamel could shed light on more appropriate management strategies for these developmental defects.
Publisher: Elsevier BV
Date: 02-2008
DOI: 10.1016/J.ARCHORALBIO.2007.08.007
Abstract: The aim of the present study is to investigate the ultrastructural changes within the different zones of carious dentine and compare those changes with sound dentine. Transmission electron microscopy and electron diffraction techniques were used to investigate the effect of caries on the inorganic phase of dentine. Areas of interest were identified with optical and scanning electron microscopes. The results demonstrated that the intertubular mineral crystallites decrease in size as caries lesion progresses. In the transparent zone of carious lesion, both intratubular and intertubular dentine consisted of nano-size apatetic crystallites with smaller size in the former. The intratubular mineral phase in transparent zone was found to be chemically similar to the intertubular dentin. The study suggests that a 'dissolution and precipitation' mechanism is important in understanding the process of formation of intratubular dentine within the transparent zone induced by caries attack. The observed partial demineralisation of intertubular dentine in transparent zone is discussed in terms of dissolution of tubule microbranches and exposure of intertubular dentin to acids.
Publisher: Wiley
Date: 09-09-2011
DOI: 10.1111/J.1708-8208.2009.00205.X
Abstract: Atraumatic preparation of the osteotomy site is critical for osseointegration. This study aimed to investigate the effects of multiple usages of dental implant drills on bone temperature changes and to examine the cutting surfaces of these drills under a scanning electron microscope (SEM). The implant osteotomy procedure was adapted to the experimental setting to simulate wear on implant drills by preparing bovine ribs using a constant drilling force. Thermocouples were placed in the specimens to record temperature changes. SEM images of the drills were taken, and elemental spectroscopic analysis was performed. Temperatures measured in the bone adjacent to the implant site did not exceed 27.7°C during the experiment. Spectroscopic elemental analysis indicated that two of the drills were of a stainless steel composition, and the other drill consisted of a tungsten carbide-coated stainless steel. The tungsten carbide-coated bur had the lowest overall drilling temperatures and showed the least surface corrosion and plastic deformation. SEM analysis showed degradation of the cutting surfaces of the burs although the plastic deformation and surface wear did not appear to affect the cutting temperatures. Surface corrosion was observed on the cutting surfaces. Drills used for up to 50 osteotomies do not appear to elevate bone temperatures to a harmful level. However, drill corrosion is potentially important in determining the life span of implant burs.
Publisher: AIP Publishing
Date: 20-11-2000
DOI: 10.1063/1.1328047
Abstract: Wurtzite GaN films grown on sapphire substrates are studied by nanoindentation with a spherical indenter. No systematic dependence of the mechanical properties of GaN epilayers on the film thickness (at least for thicknesses from 1.8 to 4 μm) as well as on doping type is observed. Slip is identified as one of the physical mechanisms responsible for plastic deformation of GaN and may also contribute to the “pop-in” events observed during loading. No visible material cracking is found even after indentations at high loads (900 mN), but a pronounced elevation of the material surrounding the impression is observed.
Publisher: Elsevier BV
Date: 02-2005
DOI: 10.1016/J.AJODO.2003.12.021
Abstract: The aims of this investigation were to evaluate the hardness and elastic modulus of untreated human premolar cementum and to investigate the changes after application of light and heavy orthodontic forces. Thirty-six maxillary and mandibular first premolars were collected from 16 prospective orthodontic patients. The patients were assigned to 1 of 2 groups. Group I (light force) consisted of 8 subjects (4 male, 4 female, mean age 14.8 years) who had 25 g of buccally directed orthodontic force applied to the first premolars on 1 side. Group II (heavy force) consisted of 9 subjects (7 male, 2 female, mean age 13.8 years) who had 225 g of buccally directed orthodontic force applied to first premolars on 1 side. Contralateral premolars served as the control in both groups. The force was applied for 4 weeks then each first premolar was extracted and stored in deionized water. Physical properties were tested on unprepared cementum on buccal and lingual surfaces at the cervical, middle, and apical thirds with an ultra-micro-indentation system. Mean (+/- standard deviation) hardness of the untreated cementum at the cervical, middle, and apical thirds, respectively, was 0.25 +/- 0.09 GPa, 0.24 +/- 0.07 GPa, and 0.18 +/- 0.06 GPa on the buccal surface and 0.24 +/- 0.08 GPa, 0.24 +/- 0.06 GPa, and 0.21 +/- 0.06 GPa on the lingual surface. Mean elastic modulus at the cervical, middle, and apical thirds, respectively, was 4.4 +/- 2.4 GPa, 3.4 +/- 2.0 GPa, and 2.4 +/- 1.8GPa on the buccal surface and 3.8 +/- 2.1 GPa, 3.2 +/- 1.4 GPa, and 2.4 +/- 1.5 GPa on the lingual surface. The mean hardness and elastic modulus of untreated human premolar cementum gradually decreased from cervical to apical regions of the buccal and lingual surfaces. A similar decrease was observed in the experimental teeth of light-force and heavy-force groups. There were no statistically significant differences between the control and experimental teeth this is probably due to large intrain idual variation.
Publisher: Elsevier BV
Date: 07-2019
DOI: 10.1016/J.DENTAL.2019.03.012
Abstract: To measure the elastic modulus of three ceramic-composite CAD/CAM materials at three different microstructural dimensions: macro, micro, and nano. Three novel ceramic-composite CAD/CAM materials (Enamic, Lava Ultimate, and Cerasmart) were investigated. Rectangular cross-sections 10 × 5.7 × 1 mm At the macro level Enamic showed the highest elastic modulus, followed by Lava Ultimate and Cerasmart respectively (p < 0.001). Measurements at the micro and nano level resulted in bimodal distributions of the elastic modulus values associated with the various phases present with values higher and lower than measured at the macro level. Only at the nano-level were the various phases of Cerasmart able to be distinguished. The tested materials showed different elastic modulus at the different size or hierarchical levels that enabled comparison with the hierarchical values of enamel. Studying the mechanical properties of these novel materials at different size or hierarchical scales can help to understand their potential clinical performance, such as structural durability and opposing tooth wear and lead to more biomimetic like dental restorative materials.
Publisher: Springer Science and Business Media LLC
Date: 02-1980
DOI: 10.1007/PL00020072
Publisher: Elsevier BV
Date: 07-2012
Publisher: Public Library of Science (PLoS)
Date: 02-12-2209
DOI: 10.1371/JOURNAL.PONE.0285850
Abstract: Anorexia is experienced by most people with lung cancer during the course of their disease and treatment. Anorexia reduces response to chemotherapy and the ability of patients to cope with, and complete their treatment leading to greater morbidity, poorer prognosis and outcomes. Despite the significant importance of cancer-related anorexia, current therapies are limited, have marginal benefits and unwarranted side effects. In this multi-site, randomised, double blind, placebo controlled, phase II trial, participants will be randomly assigned (1:1) to receive once-daily oral dosing of 100mg of anamorelin HCl or matched placebo for 12 weeks. Participants can then opt into an extension phase to receive blinded intervention for another 12 weeks (weeks 13–24) at the same dose and frequency. Adults (≥18 years) with small cell lung cancer (SCLC) newly diagnosed with planned systemic therapy OR with first recurrence of disease following a documented disease-free interval ≥6 months, AND with anorexia (i.e., ≤ 37 points on the 12-item Functional Assessment of Anorexia Cachexia Treatment (FAACT A/CS) scale) will be invited to participate. Primary outcomes are safety, desirability and feasibility outcomes related to participant recruitment, adherence to interventions, and completion of study tools to inform the design of a robust Phase III effectiveness trial. Secondary outcomes are the effects of study interventions on body weight and composition, functional status, nutritional intake, biochemistry, fatigue, harms, survival and quality of life. Primary and secondary efficacy analysis will be conducted at 12 weeks. Additional exploratory efficacy and safety analyses will also be conducted at 24 weeks to collect data over longer treatment duration. The feasibility of economic evaluations in Phase III trial will be assessed, including the indicative costs and benefits of anamorelin for SCLC to the healthcare system and society, the choice of methods for data collection and the future evaluation design. Trial registration. The trial has been registered with the Australian New Zealand Clinical Trials Registry [ACTRN12622000129785] and approved by the South Western Sydney Local Health District Human Research Ethics Committee [2021/ETH11339]. rial-detail/ACTRN12622000129785 .
Publisher: S. Karger AG
Date: 2008
DOI: 10.1159/000128559
Abstract: The aim of this study was to compare cross-sectional nanohardness, measured using an ultra-microindentation system, with mineral content, from transversal microradiography, of artificial enamel caries lesions. Sections (85 ± 10 µm) from 16 bovine enamel s les with artificial caries were prepared. The mineral content and cross-sectional nanohardness at known depths from the surface were compared. Both methods showed lesion profiles with a surface layer. The determination of nanohardness seems limited to lesions with a mineral content vol%. There was a moderate linear relationship between mineral content and the square root of nanohardness (R sup /sup = 0.81). It was concluded that the conversion of cross-sectional hardness into mineral content remains questionable and cannot be recommended.
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B806884D
Abstract: Laboratory micro-CT systems, although limited by beam hardening effect and instability of the source, have been utilized to measure mineral density in combination with specific image processing methods. However, few attempts have been made to accurately determine mineral density profiles in dentine due to the lack of suitable calibration standards. The aim of this study was to develop a calibration method to evaluate mineral density profiles in dentine including changes associated with dentinal caries. A series of K(2)HPO(4) solution phantoms in a concentration range between 0 and 0.9 g cm(-3)--coupled to a set of water infiltrated porous solid hydroxyapatite (HA) phantoms, with mineral densities ranging from 1.52 to 2.08 g cm(-3), was used in this investigation. First we evaluated the micrometer-scale homogeneity and noise in the HA phantoms using a commercial laboratory micro-CT system. Then an experimental validation was performed of the linearity over the entire density range of these two different calibration materials. The results show the HA phantoms extended the calibration curve obtained from K(2)HPO(4) solution phantoms to densities as high as 2.08 g cm(-3) the linearity remains stable at different energy levels. Finally, compared to the reference micro-CT calibration methods, the advantages of this new method are discussed. We conclude that this calibration method allows a more rational assessment of mineral density of dentine by micro-CT and has a promising potential for future studies.
Publisher: Elsevier BV
Date: 10-1997
Publisher: Elsevier BV
Date: 10-2008
DOI: 10.1016/J.JDENT.2008.05.011
Abstract: To identify the intrinsic nano-scale wear mechanisms of enamel by comparing it with that of highly brittle glass, and highly ductile copper and silver monocrystals. A sharp cube corner indenter tip (20-50 nm radius) was used to abrade glass, enamel as well as copper and silver monocrystals. Square abraded areas (5 microm x 5 microm, 10 microm x 10 microm) were generated with loads of 50 microN for enamel and 100 microN for the remaining materials (2D abrasion). The normal load and displacement data were utilized in a complementary manner to support the comparison. In addition normal and lateral forces were simultaneously measured along 10 microm single scratched lines (1D abrasion). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were also used to characterise the worn areas and debris. The sharp tip cuts into and ploughs the specimens creating a wedge or ridge of material ahead of itself which eventually detaches, for the ductile materials and at high loads in enamel. For glass and enamel at low loads, the indenter tip ploughs into the material and the removed material is redistributed and pressed back into the abraded area. The wear behaviour of enamel at the nano-level resembles that obtained with glass at low loads (50 microN) and that obtained with metal mono-crystals at high load (100 microN). The role of the microstructural heterogeneity in the wear behaviour of enamel is considered in the discussion. The relevance to clinical wear of enamel is also considered.
Publisher: Operative Dentistry
Date: 07-2011
DOI: 10.2341/10-414-L
Abstract: Fluoride containing resin composites and especially those containing pre reacted glass ionomer fillers could be employed to great benefit in treating high caries risk patients in situations where glass ionomers may be unsuitable particularly in high load bearing or aesthetically critical locations.
Publisher: Springer Science and Business Media LLC
Date: 07-1975
DOI: 10.1007/BF00541407
Publisher: Wiley
Date: 04-1999
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.DENTAL.2014.08.363
Abstract: To evaluate the efficacy on flexural properties of flowable dental resin composite reinforced with short glass fiber of different aspect ratios (ARs) and volume percent loadings. It is hypothesized that with the addition of randomly oriented fibers it is possible to significantly improve flexural strength and modulus while maintaining flowability. Ten groups of s les with varying glass fiber volume loads (0, 5%, 10%, 20%, 40% and 60%) and three different ARs (5.2, 68 and 640) were tested in three point bending to fracture according to ISO 4049. A flowable resin composite was used as the control and also as the filled resin composite that was subsequently reinforced with fibers. Load deflection results were used to calculate flexural strength and flexural modulus. SEM images were used to determine the mode(s) of failure, to describe surface features of reinforcement and were correlated with force displacement graphs. All results were statistically analysed using ANOVA followed by post hoc Tukey's test. Level of significance was set at 0.05. When compared to the "sculptable" control (68.6 vol% filler loaded) results for flexural strength varied from a mean reduction of 42% (p>0.05) for the low AR group to an increase of 77% (p<0.001) for the high AR s les. Flexural modulus results varied from a low of 6.6 [0.67] GPa for the non reinforced spatulated control to 20.3 [1.31] GPa (p 0.05) and comparable modulus. This study shows that short and very short glass fibers can significantly reinforce flowable dental composite. The fiber's aspect ratio was shown to be more important than volume loading for flexural strength. It appears possible to produce a light cured short glass fiber reinforced flowable material with superior flexural properties compared to conventional universal composites.
Publisher: Elsevier BV
Date: 09-2011
DOI: 10.1016/J.JDENT.2011.05.006
Abstract: The aim of this study was to evaluate the addition of titanium dioxide (TiO(2)) nanoparticles to a conventional glass-ionomer (GI) on physical and antibacterial properties. TiO(2) nanoparticles were incorporated into the powder component of Kavitan(®) Plus (SpofaDental, Czech Republic) at 3%, 5% and 7% (w/w). Unblended powder was used as control. Fracture toughness, compressive strength, flexural strength and microtensile bond strength were evaluated using a universal testing machine. Surface microhardness was measured using Vickers microhardness tester. Setting time was determined as specified in the ISO standard. The antibacterial activity was evaluated using direct contact test against Streptococcus mutans. Fluoride release and SEM analysis were carried out. Data were analysed using ANOVA and Tukey's test. GI-containing 3% and 5% (w/w) TiO(2) nanoparticles improved the fracture toughness, flexural strength and compressive strength compared to the unmodified GI. However, a decrease in the mechanical properties was found for GI-containing 7% (w/w) TiO(2) nanoparticles. GI-containing 5% and 7% (w/w) TiO(2) nanoparticles compromised the surface microhardness. Setting time of GI-containing TiO(2) nanoparticles decreased but the values remained within ISO limits. The addition of TiO(2) nanoparticles to the conventional GI did not compromise its bond strength with dentine or fluoride release of the GI. GI-containing TiO(2) nanoparticles possessed a potent antibacterial effect. GI-containing 3% (w/w) TiO(2) nanoparticles is a promising restorative material with improved mechanical and antibacterial properties. This novel experimental GI may be potentially used for higher stress-bearing site restorations such as Class I and II.
Publisher: Springer Science and Business Media LLC
Date: 11-1986
DOI: 10.1007/BF01742233
Publisher: Elsevier BV
Date: 09-2014
DOI: 10.1016/J.PROSDENT.2013.12.009
Abstract: Cobalt-chromium (CoCr) metal ceramic restorations are known to be more susceptible to cracking and interfacial failures. This is partially related to their high potential for oxidation compared with restorations made with high noble alloys. One approach that may improve their compatibility is the use of bonding agents. The purpose of this study was to investigate the influence of a tungsten metal conditioner on the adhesion and residual stress of porcelain bonded to a cobalt-chromium alloy. Eighty-one metal-porcelain bilayered specimens were manufactured and tested with a 4-point bend for adhesion and with Vickers indentation for residual stress determination. The strain energy release rate for adhesion energy and indentation residual stress was evaluated for specimens layered with and without tungsten (W) metal conditioner. Subsequent scanning electron microscopy and energy dispersive spectrometry were performed to identify fracture behavior and chemical and phase compositions. The average strain energy release rate of the specimen group tested without the W metal conditioner was significantly higher (P<.05) (44.70 J/m(2)) than that of the group with the W metal conditioner (28.65 J/m(2)). The average residual stress of the specimen group with (0.1 MPa) and without (1.61 MPa) the W metal conditioner did not differ significantly. Scanning electron microscopy and energy dispersive spectrometry analysis enabled the modes of failure to be determined and indicated the mechanisms by which the W metal conditioner influenced the bond. The W metal conditioner used in this study significantly lowered the strain energy release rate of the porcelain-cobalt-chromium interface and did not have a significant influence on the residual stress state of the porcelain.
Publisher: Wiley
Date: 1991
Publisher: Elsevier BV
Date: 1991
Publisher: Springer Science and Business Media LLC
Date: 11-1996
DOI: 10.1007/BF01152149
Publisher: Informa UK Limited
Date: 09-1990
Publisher: Elsevier BV
Date: 06-2008
DOI: 10.1016/J.BIOMATERIALS.2008.02.022
Abstract: Tooth enamel is the hardest tissue in the human body with a complex hierarchical structure. Enamel hypomineralisation--a developmental defect--has been reported to cause a marked reduction in the mechanical properties of enamel and loss of dental function. We discover a distinctive difference in the inelastic deformation mechanism between sound and hypomineralised enamels that is apparently controlled by microstructural variation. For sound enamel, when subjected to mechanical forces the controlling deformation mechanism was distributed shearing within nanometre thick protein layer between its constituent mineral crystals whereas for hypomineralised enamel microcracking and subsequent crack growth were more evident in its less densely packed microstructure. We develop a mechanical model that not only identifies the critical parameters, i.e., the thickness and shear properties of enamels, that regulate the mechanical behaviour of enamel, but also explains the degradation of hypomineralised enamel as manifested by its lower resistance to deformation and propensity for catastrophic failure. With support of experimental data, we conclude that for sound enamel an optimal microstructure has been developed that endows enamel with remarkable structural integrity for durable mechanical function.
Publisher: Elsevier BV
Date: 03-2017
DOI: 10.1016/J.ACTBIO.2016.12.007
Abstract: This paper presents a simple analysis based upon Darcy's Law and indentation contact mechanics to determine the effective hydraulic conductivity and elastic modulus of fluid filled tissues. The approach is illustrated with the mechanical response of the human ocular surface using a 500μm radius spherical tipped indenter. Indentations of various regions of the ocular surface including the corneal stroma, limbal region and sclera have been conducted. Force-control indentations were made to a maximum force, which was maintained before unloading. Measurements of the indentation response of cornea at three different loading rates were also made. Elastic like response was observed during loading, which was followed by extensive creep prior to unloading. This manuscript attempts to provide a relatively simply model for the contact loading of fluid containing tissues and materials. It shows that the response of such materials provides a basis for determining the effective modulus and effective hydraulic conductivity (permeability) in much the same manner that hardness and modulus do for the indentation of elastic-plastic materials. Eye tissue with its anisotropic elastic and permeability properties is used to illustrate the approach.
Publisher: Oxford University Press (OUP)
Date: 08-06-2006
DOI: 10.1093/EJO/CJI115
Abstract: This study was performed to assess the relationship between the magnitude of orthodontic force and physical properties of in idual human cementum, and to identify the sites that may be predisposed to root resorption. The findings may assist in relating physical properties of dental root cementum and its susceptibility to root resorption. Sixteen maxillary first premolar teeth were selected in eight orthodontic patients (three males and five females), mean age 14.8 years (range 11.2-17.5 years), requiring first premolar extractions. In each patient, a light orthodontic force of 25 cN was applied buccally using a sectional archwire on the first premolar on one side, while a heavy force of 225 cN was applied to the contralateral side. The teeth were extracted 4 weeks after initial force application. Hardness and elastic modulus were measured on the buccal and the lingual surfaces of the cementum at the cervical, middle, and apical third of the root. The results showed that the mean hardness and elastic modulus of cementum in the light force group were greater than in the heavy force group at all positions. There were highly significant differences in both hardness and elastic modulus between the heavy and light force groups (P < 0.01). The mean hardness and elastic modulus of cementum gradually decreased from the cervical to the apical regions for buccal as well as lingual surfaces in both groups. There was, however, an insignificant difference between hardness and elastic modulus on the buccal surface compared with the lingual surface (P < 0.05). It was concluded that the hardness and elastic modulus of cementum were affected by the application of orthodontics forces.
Publisher: Elsevier BV
Date: 04-2022
DOI: 10.1016/J.JMBBM.2013.06.004
Abstract: Forensic biomechanics is increasingly being used to explain how observed injuries occur. We studied infant rib fractures from a biomechanical and morphological perspective using a porcine model. We used 24, 6th ribs of one day old domestic pigs Sus scrofa, ided into three groups, desiccated (representing post-mortem trauma), fresh ribs with intact periosteum (representing peri-mortem trauma) and those stored at -20°C. Two experiments were designed to study their biomechanical behaviour fracture morphology: ribs were axially compressed and subjected to four-point bending in an Instron 3339 fitted with custom jigs. Morphoscopic analysis of resultant fractures consisted of standard optical methods, micro-CT (μCT) and Scanning Electron Microscopy (SEM). During axial compression fresh ribs did not fracture because of energy absorption capabilities of their soft and fluidic components. In flexure tests, dry ribs showed typical elastic-brittle behaviour with long linear load-extension curves, followed by short non-linear elastic (hyperelastic) behaviour and brittle fracture. Fresh ribs showed initial linear-elastic behaviour, followed by strain softening and visco-plastic responses. During the course of loading, dry bone showed minimal observable damage prior to the onset of unstable fracture. Frozen then thawed bone showed similar patterns to fresh bone. Morphologically, fresh ribs showed extensive periosteal damage to the tensile surface with areas of collagen fibre pull-out along the tensile surface. While all dry ribs fractured precipitously, with associated fibre pull-out, the latter feature was absent in thawed ribs. Our study highlights the fact that under controlled loading, fresh piglet ribs (representing perimortem trauma) did not fracture through bone, but was associated with periosteal tearing. These results suggest firstly, that complete lateral rib fracture in infants may in fact not result from pure compression as has been previously assumed and secondly, that freezing of bone during storage may affect its fracture behaviour.
Publisher: Elsevier BV
Date: 03-2003
DOI: 10.1016/S0142-9612(02)00464-7
Abstract: To evaluate the bonding strength of the interfaces within the cemented arthroplasty system, various mechanical tests have been used. Conventional push-out and pull-out tests cannot reveal the actual bonding property of the interface because of the significant influence of surface roughness on the measured adhesion and the failure to account for the mismatch of elastic modulus across the interface. An alternative fracture mechanics approach, which considers the mix of opening and shear modes of the crack tip loading associated with the testing system and the elastic mismatch of materials across the interface, was used to evaluate the bonding ability of various cements. The four-point bend interfacial delamination test by Charalambides et al. (J. Appl. Mech. 56 (1989) 77 Mech. Mater. 8 (1990) 269) was used to quantify the bonding ability of cements. This method is arguably more suitable since the applied loading mode is comparable to the nature of loading within the prosthetic system, which is primarily bending. The bovine bone specimens were polished to mirror finish to eliminate bonding by mechanical interlocking. The results revealed minimal bonding for the conventional bone cement (PMMA) whereas substantial bonding was evident for the glass-ionomer cements tested. However, only the conventional glass-ionomer cements showed evidence of bonding on testing, while the resin-modified glass-ionomer cement (poly-HEMA) did not. The latter appeared to debond before testing because of excessive expansion stresses associated with swelling in water.
Publisher: Springer Science and Business Media LLC
Date: 2001
Publisher: American Chemical Society (ACS)
Date: 27-10-2004
DOI: 10.1021/ES0492900
Abstract: Ice cores from glaciers situated near anthropogenic sources of air pollution provide important archives of the emissions of species with short atmospheric lifetimes. Here we present the history of atmospheric Pu fallout reconstructed from an ice core from the Belukha glacier in the Siberian Altai. Fourteen ice core s les covering the time period 1941-1986 were selected for Pu analysis, chemically processed, and measured using accelerator mass spectrometry. The Pu concentration peaks in 1963, coinciding with the maximum of the nuclear weapons tests and in concordance with the 3H activity concentration peak. The shapes of the 239Pu and 3H profiles reflect two main periods of atmospheric nuclear test activity: premoratorium testing before 1958 and postmoratorium testing in 1961 and 1962. Premoratorium tests contribute about 45% of the integrated Pu inventory. The average 240Pu/239Pu isotopic ratio is 0.18 +/- 0.05, indicating that a large majority of the Pu in the Belukha glacier originates from global stratospheric fallout rather than from direct tropospheric input.
Publisher: Springer Science and Business Media LLC
Date: 1975
DOI: 10.1007/BF00541038
Publisher: Springer Science and Business Media LLC
Date: 1996
DOI: 10.1007/BF00368992
Publisher: Springer Science and Business Media LLC
Date: 1981
DOI: 10.1007/BF00552069
Publisher: IOP Publishing
Date: 25-01-2001
DOI: 10.1088/0031-9155/46/2/319
Abstract: This study investigates the accuracy and reliability of a novel handheld indentation system designed to ascertain the dynamic biomechanical properties of articular cartilage. A series of standard elastomers were assessed with both the handheld indentation system and a bench-top dynamic indentation system to assess the accuracy of the instrument. Interoperator and intraoperator experiments were undertaken to investigate the reliability of the system when used by an in idual operator and by five different operators. Intraclass coefficients (Rho) were derived using a random effects model. The system was then used to ascertain the topographical variation in the shear moduli and phase lag of articular cartilage across normal ovine tibial plateaux. The system was shown to be highly accurate (R2 = 0.97), and had excellent reliability when measuring the dynamic shear modulus of articular cartilage (interoperator Rho = 0.75, intraoperator Rho = 0.79). Measurement of static shear modulus was less reliable (interoperator Rho = 0.15, intraoperator Rho = 0.52), but may be improved by monitoring the load applied to the instrument by the operator. The instrument was used to differentiate between different regions of cartilage and generated a topographical map of an ovine tibial plateau. The cartilage located beneath the menisci was 200-500% stiffer than the cartilage that was not covered by the menisci, while the phase lag was almost constant (10+/-2 SD) over the entire tibial plateau. The system was shown to be an accurate and reliable tool for rapidly assessing the dynamic biomechanical properties of articular cartilage, while being small enough to be used arthroscopically.
Publisher: Elsevier BV
Date: 10-2009
DOI: 10.1016/J.JMBBM.2008.11.007
Abstract: Numerous studies have shown that human bone has the ability to remodel itself to better adapt to its biomechanical environment by changing both its material properties and geometry. As a consequence of the rapid development and extensive applications of dental implants, the effect of bone remodeling on the success of a dental restorative surgery is becoming critical for implant design and pre-surgical assessment. This article provides an extensive review on the issues of mandibular and maxillary bone remodeling as a result of dental implantation. Following the success of remodeling-driven orthopedic design from the long bone community, substantial clinical/experimental data of implantation have been driving the development of corresponding remodeling laws and algorithms to various dental settings, of which it is believed to contain potential to significantly impact on futuristic dental implant design. In this paper, the published remodeling data is analyzed and different biomechanical remodeling stimuli are assessed. The established relationships between bone density and corresponding mechanical properties are outlined and a range of potential methods of predicting the mandible and maxilla remodeling are critically evaluated and compared. It is anticipated that this will provide a better understanding of implant-induced bone remodeling and help develop a new design framework for patient-specific dental implantation.
Publisher: Springer Science and Business Media LLC
Date: 05-1988
DOI: 10.1007/BF01115724
Publisher: Elsevier BV
Date: 10-2013
DOI: 10.1016/J.DENTAL.2013.07.012
Abstract: To test the null hypothesis that polymerization-induced stress was not influenced by cavity dimensions and geometries. Four experimental groups, with different C-factors and specimen volumes were defined using bottom-less glass disks (height: 1 or 2mm) with a central hole 3 or 6mm in diameter, and 3mm wall thickness. Another four groups were created by bonding a glass plate to the bottom of the disks. Additionally, disks with 2-mm height, 3mm in cavity diameter, and 4.5-mm thick walls were prepared. Vickers indents (9.8N, 20s) were made at the top surface at 600μm from the cavity margin. The lengths of the indentation diagonal and the corner cracks parallel to the cavity margin were measured. Ten minutes after restoration (Majesty Esthetic, Kuraray), cracks were re-measured. Stresses at the indent site were calculated based on glass fracture toughness and increase in crack length. Data were subjected to ANOVA/Tukey or Kruskal-Wallis/Mann-Whitney tests (alpha: 5%, n=8). Finite element analysis (FEA) was used to estimate stress at the interface and the effective structural rigidity of the substrate. Overall, for experimental and FEA results, cavities developed higher stress than bottom-less disks. Increasing wall thickness did not affect stress. When similar geometries and C-factors were compared, higher volumes developed higher stress and had greater incidence of margin cracking. C-factor is a suitable predictor for polymerization stress in low compliance environments, particularly due to its simplicity. However, the influence of cavity size cannot be disregarded especially for the development of marginal cracking. The interaction between size, geometry and stiffness is likely to become more complex according to the complexity of the cavity shape.
Publisher: Wiley
Date: 29-10-2016
DOI: 10.1002/CNM.2749
Abstract: Layered all-ceramic systems have been increasingly adopted in major dental prostheses. However, ceramics are inherently brittle, and they often subject to premature failure under high occlusion forces especially in the posterior region. This study aimed to develop mechanically sound novel topological designs for all-ceramic dental bridges by minimizing the fracture incidence under given loading conditions. A bi-directional evolutionary structural optimization (BESO) technique is implemented within the extended finite element method (XFEM) framework. Extended finite element method allows modeling crack initiation and propagation inside all-ceramic restoration systems. Following this, BESO searches the optimum distribution of two different ceramic materials, namely porcelain and zirconia, for minimizing fracture incidence. A performance index, as per a ratio of peak tensile stress to material strength, is used as a design objective. In this study, the novel XFEM based BESO topology optimization significantly improved structural strength by minimizing performance index for suppressing fracture incidence in the structures. As expected, the fracture resistance and factor of safety of fixed partial dentures structure increased upon redistributing zirconia and porcelain in the optimal topological configuration. Dental CAD/CAM systems and the emerging 3D printing technology were commercially available to facilitate implementation of such a computational design, exhibiting considerable potential for clinical application in the future. Copyright © 2015 John Wiley & Sons, Ltd.
Publisher: Elsevier BV
Date: 10-2011
DOI: 10.1016/J.JMBBM.2011.03.026
Abstract: Nanoindentation is a useful technique for probing the mechanical properties of bone, and finite element (FE) modeling of the indentation allows inverse determination of elastoplastic constitutive properties. However, all but one FE study to date have assumed frictionless contact between indenter and bone. The aim of this study was to explore the effect of friction in simulations of bone nanoindentation. Two-dimensional axisymmetric FE simulations were performed using a spheroconical indenter of tip radius 0.6 μm and angle 90°. The coefficient of friction between indenter and bone was varied between 0.0 (frictionless) and 0.3. Isotropic linear elasticity was used in all simulations, with bone elastic modulus E = 13.56 GPa and Poisson's ratio of 0.3. Plasticity was incorporated using both Drucker-Prager and von Mises yield surfaces. Friction had a modest effect on the predicted force-indentation curve for both von Mises and Drucker-Prager plasticity, reducing maximum indenter displacement by 10% and 20% respectively as friction coefficient was increased from zero to 0.3 (at a maximum indenter force of 5 mN). However, friction has a much greater effect on predicted pile-up after indentation, reducing predicted pile-up from 0.27 to 0.11 μm with a von Mises model, and from 0.09 to 0.02 μm with Drucker-Prager plasticity. We conclude that it is potentially important to include friction in nanoindentation simulations of bone if pile-up is used to compare simulation results with experiment.
Publisher: Wiley
Date: 02-05-2011
DOI: 10.1002/SIA.3683
Publisher: Elsevier BV
Date: 2017
DOI: 10.1016/J.JDENT.2016.11.007
Abstract: The aim of this study was to characterize the mineral density parameters through natural enamel brown spot lesions (BSLs) and to visualize and map their mineral distribution pattern in comparison to enamel whitespot lesions (WSLs). Study specimens included seventeen proximal WSLs (ICDAS 1, 2), seventeen proximal BSLs and seventeen sound proximal specimens (ICDAS 0) collected from The Oral Surgery Department at Sydney Dental Hospital, Sydney, Australia. Imaging was undertaken using a high resolution, desktop micro-computed tomography system. A calibration equation was used to transform the grey level values of the images into true mineral density values. The qualitative analysis and the quantification of the lesion parameters including the mineral density and the thickness of the enamel lesion surface layer were performed using mineral density profiles plotted in FIJI and the visualized mineral maps in MATLAB respectively. The maps of brownspot lesions revealed irregular demineralization patterns with faint boundaries and outlines. The regular triangular shape of proximal lesions was recognizable only in some parts of in idual BSLs or was completely unrecognizable within the entire lesion. Scattered free-form areas of high density enamel were observed within or close to the surface of BSLs. A layer of high density enamel with a mineral density close to that of sound enamel was observed in all of the BSLs. The mean mineral density of the body of BSLs, including the scattered areas of high mineral density, was significantly higher than the corresponding values in white-spot lesions. The mean thickness of the surface layer in BSLs (79±15μm) was also significantly higher than white-spot lesions (51±11μm) (p<0.05). This study demonstrated that the mineralization parameters such as density and the thickness of the surface layer as well as distribution patterns through natural enamel brown spot lesions (BSLs) are different from enamel white-spot lesions (WSLs). The higher mineral density of the body of the lesion and the increased thickness of the surface layer in brown spot enamel lesions may suggest possible subsurface remineralization in the majority of naturally arrested BSLs.
Publisher: Elsevier BV
Date: 12-2012
DOI: 10.1016/J.ACTBIO.2012.08.006
Abstract: The objectives of this study were to identify the effect of design parameters, namely marginal thickness, degree of convergence and the different interfacial conditions, on the initial failure load that induces cracking from the margin in glass-simulated dental crowns. Crown-like glass cylinders were prepared to simulate posterior all-ceramic crowns with two different marginal thicknesses (0.8 or 1.2mm) and degrees of convergence (6° or 12°). A three-step bonding system was used complementarily with a silane coupling agent to adhesively bond the specimens to resin dies. The crowns were subjected to an axial applied load to generate hoop tensile stress at the crown margin. The entire loading and fracture processes were recorded by video camera. The loading data were compared with the other two interfacial treatments (Vaseline grease and directly poured uncured resin on glass). The Weibull distribution was used to statistically analyze the characteristic failure load and the mean values. The fracture surfaces were fractographically analyzed along with the load-displacement curves, and the degrees of crack stability for each parameter were also identified. It was found that there is no difference in the initial failure load between the different marginal thicknesses in all interfacial conditions. The bonded crowns present more resistance to crack propagation. The higher convergence crown preparation can reduce the initial failure load at the crowns' margin, which can be resisted by a strongly bonded interface. Clear interactions between margin design parameters and their effects on the stress development and crack propagation are necessary to develop an appropriate design of all-ceramic crowns.
Publisher: Wiley
Date: 11-03-2009
DOI: 10.1111/J.1600-0501.2008.01666.X
Abstract: To review the literature on mandibular single-implant overdentures (opposing complete maxillary dentures), and present surgical and prosthodontic perspectives of a novel approach for this treatment option. An electronic search through the databases of Pubmed, Embase and Medline using the linked key words 'mandibular single implant overdentures' was performed. The search was limited to English language articles published up to August 2008. Hand searches through articles retrieved from the electronic search, peer-reviewed journals and recent conference proceedings were also conducted. A limited number of reports were identified on mandibular single-implant overdentures (opposing maxillary complete dentures). They comprised of case-series reports, short-term prospective trials and current randomized-controlled clinical trials. Different loading protocols with different implant systems have been used, but always with regular diameter implants. Specific anatomical and vascular dangers of the mandibular midline symphysis are identified including a novel surgical approach using a currently available short, wide diameter tapered implant. In addition, the prosthodontic rationale for using a larger attachment system (incorporating a platform switch) for mandibular single-implant overdentures is described. The review reveals that there is a lack of published randomized clinical trials using mandibular single-implant overdentures, opposing maxillary complete dentures. Without the evidence from randomized clinical trials, routine use of this novel approach cannot be recommended, compared with using regular diameter implants and matching attachment systems.
Publisher: Springer Science and Business Media LLC
Date: 04-1993
Abstract: The recently reported hysteretic behavior of silicon under indentation (Clarke et al. 1 and Pharr et al. 2-5 ) is investigated using an ultra-micro-indentation system with an 8.5 μm spherical-tipped indenter. The onset of “plastic” behavior during loading and hysteresis during unloading was readily observed at loads in excess of 70 mN. Cracking about the residual impression was observed only at loads of 350 mN and higher. An analysis of the data is presented that estimates the following: (1) the initial onset of deformation occurs at a mean pressure of 11.8 ± 0.6 GPa, (2) the mean pressure at higher loads is 11.3 ± 1.3 GPa, and (3) the hysteretic transition on unloading occurs at mean pressures between 7.5 and 9.1 GPa. These values are in good agreement with the accepted literature values for the known silicon transformation pressures. A simulation of the force-displacement data based on the analysis and model is presented and is found to fit the observations very well.
Publisher: Wiley
Date: 25-05-2016
DOI: 10.1111/JOOR.12411
Abstract: Implant-supported fixed partial denture with cantilever extension can transfer the excessive load to the bone around implants and stress/strain concentration potentially leading to bone resorption. This study investigated the effects of implant configurations supporting three-unit fixed partial denture (FPD) on the stress and strain distribution in the peri-implant bone by combining clinically measured time-dependent loading data and finite element (FE) analysis. A 3-dimensional mandibular model was constructed based on computed tomography (CT) images. Four different configurations of implants supporting 3-unit FPDs, namely three implant-supported FPD, conventional three-unit bridge FPD, distal cantilever FPD and mesial cantilever FPD, were modelled. The FPDs were virtually inserted to the molar area in the mandibular FE models. The FPDs were loaded according to time-dependent in vivo-measured 3-dimensional loading data during chewing. The von Mises stress (VMS) and equivalent strain (EQS) in peri-implant bone regions were evaluated as mechanical stimuli. During the chewing cycles, the regions near implant necks and bottom apexes experienced high VMS and EQS than the middle regions in all implant-supported FPD configurations. Higher VMS and EQS values were also observed at the implant neck region adjacent to the cantilever extension in the cantilevered configurations. The patient-specific dynamic loading data and CT-based reconstruction of full 3D mandibular allowed us to model the biomechanical responses more realistically. The results provided data for clinical assessment of implant configuration to improve longevity and reliability of the implant-supported FPD restoration.
Publisher: Springer Science and Business Media LLC
Date: 04-2003
Abstract: The study presents evidence of the microstructural evolution during cyclic indentation of monocrystalline silicon with a spherical indenter. Transmission electron microscopy examination of microindentation on cross-section view s les showed that the structure change in the transformation zone features a decomposition of the amorphous phase to R8/BC8 crystals. Outside the zone, cyclic loading gives rise to bending of pristine silicon, slip penetration, and radial cracking. The development of the load–displacement curves during consecutive indentations is justified in terms of the phase transformation events observed.
Publisher: IEEE
Date: 05-2009
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.JDENT.2014.03.014
Abstract: The purpose of this in vitro study was to evaluate the effect of core ceramic grinding on the fracture behaviour of bilayered lithium disilicate glass-ceramic (LDG) under two loading schemes. Interfacial surfaces of sandblasted LDG disks (A) were ground with 220 (B), 500 (C) and 1200 (D) grit silicon carbide (SiC) sandpapers, respectively. Surface roughness and topographic analysis were performed using a profilometer and a scanning electron microscopy (SEM), and then underwent retesting after veneer firing. Biaxial fracture strength (σf) and Weibull modulus (m) were calculated either with core in tension (subgroup t) or in compression (subgroup c). Failure modes were observed by SEM, and loading induced stress distribution was simulated and analyzed by finite element analysis. Statistical data analysis was performed using Kruskal-Wallis, one-way ANOVA, and paired test at a significance level of 0.05. As the grits size of SiC increased, LDG surface roughness decreased from group A to D (p<0.001), which remained unchanged after veneer firing. No difference in σf (p=0.41 for subgroups At-Dt p=0.11 for subgroups Ac-Dc), m values as well as failure modes was found among four subgroups for both loading schemes. Specimens in subgroup t showed higher σf (p<0.001) and m values than subgroup c. Stress distribution between loading schemes did not differ from each other. Cracks, as the dominant failure mode initiated from bottom tensile surface. No sign of interfacial cracking or delamination was observed for all groups. Technician grinding changed surface topography of LDG ceramic material, but was not detrimental to the bilayered system strength after veneer application. LDG bilayered system was more sensitive to fracture when loaded with veneer porcelain in tension. Within the limitations of the simulated grinding applied, it is concluded that veneer porcelain can be applied directly after technician grinding of LDG ceramic as it has no detrimental effect on the strength of bilayered structures. The connector areas of LDG fixed dental prosthesis are more sensitive to fracture compared with single crowns, and should be fabricated with more caution.
Publisher: Elsevier BV
Date: 11-1992
Publisher: Elsevier BV
Date: 03-2018
DOI: 10.1016/J.DENTAL.2017.12.010
Abstract: To evaluate the effect of different pH media on zirconia-reinforced lithium silicate glass ceramic and how they interact with opposing dentition after being aged in different pH cycling and high temperature conditions. Twenty-five rectangular shaped specimens were prepared from lithium silicate reinforced with zirconia blanks (Suprinity, Vita Zahnfabrick) and stored in different pH media (3 & 7.2) for different periods (24h & 7 days) at temperature (55°C). After their surface roughness (Ra) evaluation, aged ceramic specimens were subjected to cyclic abrasive wear with opposing natural teeth enamel for 150,000 cycles using a chewing simulator. Weight loss and Scanning Electron Microscope (SEM) images were used to evaluate the cyclic wear results. After different pH storage, ceramic group stored at 3 pH for 1-W (1 week) gave significantly higher mean Ra value (0.618μm±0.117) than control lowest mean value (0.357μm±0.054) before cyclic wear. On the other hand, it caused the least significant weight loss value (0.004gm±0.001) to opposing tooth enamel. There was significant tooth enamel weight loss (0.043gm±0.004) when opposed with ceramic group stored in 3 pH media for 24h (24-H). Their SEM images showed a prominent wear scar on enamel cusp tip. There was a significant increase in surface roughness Ra of ceramic material after abrasive cyclic wear. Great attention should be paid to Ra of this type of glass ceramic even if it is considered as minimal values. It can induce a significant amount of enamel tooth wear after a period equivalent to one year of intra-oral function rather than the significantly higher surface Ra of such ceramic type can do.
Publisher: Wiley
Date: 13-04-2017
DOI: 10.1002/CNM.2779
Abstract: Design of prosthetic implants to ensure rapid and stable osseointegration remains a significant challenge, and continuous efforts have been directed to new implant materials, structures and morphology. This paper aims to develop and characterise a porous titanium dental implant fabricated by metallic powder injection-moulding. The surface morphology of the specimens was first examined with a scanning electron microscope (SEM), followed by microscopic computerised tomography (μ-CT) scanning to capture its 3D microscopic features non-destructively. The nature of porosity and pore sizes were determined statistically. A homogenisation technique based on the Hills-energy theorem was adopted to evaluate its directional elastic moduli, and the conservation of mass theorem was employed to quantify the oxygen diffusivity for bio-transportation feature. This porous medium was found to have pore sizes varying from 50 to 400 µm and the average porosity of 46.90 ± 1.83%. The anisotropic principal elastic moduli were found fairly close to the upper range of cortical bone, and the directional diffusivities could potentially enable radial osseous tissue ingrowth and vascularisation. This porous titanium successfully reduces the elastic modulus mismatch between implant and bone for dental and orthopaedic applications, and provides improved capacity for transporting oxygen, nutrient and waste for pre-vascular network formation. Copyright © 2016 John Wiley & Sons, Ltd.
Publisher: Elsevier BV
Date: 10-2011
DOI: 10.1016/J.JMBBM.2011.03.014
Abstract: To develop an approximate analytical model that identifies the influence of both cusp angle and notch radius on the failure load of all-ceramic premolar crowns. The scatter of failure loads in a crown fracture resistance test was analyzed based on the stress intensity and stress concentration factors from mechanics models developed for simple compact tension to more sophisticated blunt V-notch specimens. Based on the same loading conditions and dimensions, the predicted loads were systematically compared with fracture loads of laboratory-tested crowns to identify the most relevant model. Finally, based upon these models a safe range of cusp angles and notch radii were identified for posterior all-ceramic crowns with various veneering materials' fracture toughness values as the selection criteria. The failure loads of the crowns were distributed in the range between the classical compact tension (lower bound) and blunt V-notch model (upper bound). Additionally, when considering the effect of different materials, the predicted trend of failure loads moves to higher loads well above typical occlusal forces when the fracture toughness of veneering porcelain is increased. The effects of notch radius on the failure load are still inconclusive due to the relatively complex shape of occlusal surfaces. Further studies on crowns with a range of material properties are required to substantiate the model. Cusp angle is a key factor that controls the stress generated at the crown fissure. This study provides the rationale for evaluating such effects and clinical guidelines for occlusal design are proposed.
Publisher: No publisher found
Date: 2018
DOI: 10.1002/JBM.A.36337
Abstract: UVA crosslinking is used for treatment of corneal diseases such as keratoconus in order to stabilize the corneal tissue by crosslinking of the collagen fibers. It has been shown that the crosslinking treatment leads to a stiffening of the central corneal tissue. However, knowledge of lateral extent of the corneal stiffening as well as a systematic study of the mechanical response of human cornea is still missing. In our study we measured the stiffness (elastic modulus) of the anterior surface of healthy and crosslinked human corneas by instrumented indentation using a spherical indenter. The results show that the stiffness of the central and paracentral cornea increased almost two times after the crosslinking but the stiffening effect rapidly decreased towards the periphery of the radiation field. These new insights into the understanding of the biomechanical response of corneal crosslinking shall contribute to a better understanding and an optimization of this perspective medical treatment. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1413-1420, 2018.
Publisher: Elsevier BV
Date: 11-2000
DOI: 10.1016/S0300-5712(00)00043-9
Abstract: Baseline information on the mechanical properties of and the effect of load upon dental hard tissue is important in the development of successful dental materials. Existing methods of measuring such properties of tissue are subject to significant experimental error. This study reports on the use of an Ultra-Micro-Indentation System (UMIS) to measure the hardness and elastic modulus of primary enamel and dentine. Primary molar teeth were sectioned, set in resin and polished. Thirty indentations were made in enamel and dentine using a Berkovitch indentor, 15 of which were subject to a load of 50mN and 15 to a load of 150mN. An automated computerised system converted the force enetration graph for each indentation in to a hardness vs depth graph from which values for the mean hardness and elastic modulus were calculated. Primary enamel had a mean hardness of 4.88+/-0.35GPa whilst the hardness of dentine was 0.92+/-0.11GPa The elastic modulus for enamel was 80.35+/-7.71GPa and that of dentine 19.89+/-1.92GPa. Using linear regression analysis a significant relationship could be shown between the hardness and the elastic modulus for both enamel and dentine when loaded to 150mN but only for dentine at 50mN (P<0.05). In general the elasticity of tooth structure increased as the hardness increased. The UMIS offers a simple and reproducible method of measuring basic mechanical properties of small s les of enamel and dentine.
Publisher: Elsevier BV
Date: 06-2012
DOI: 10.1016/J.JBIOMECH.2012.03.021
Abstract: Improved understanding of the effects of hydration and drying in mineralized tissues is highly desirable, particularly for physiologically hydrated biological materials such as dentin. We investigated the influence of hydration on the nanomechanical properties of healthy dentin and hypothesized that drying leads to an increase in indentation induced energy expenditure and hardness. Hydrated and dry dentin were tested with a UMIS set up with a Berkovich indenter at a maximum load of 50 mN. Values representative of the energy expenditure behavior were presented as dissipated energy, U(d), recovered energy, U(e), normalized energy expenditure index, ψ, and hardness, H. Energy expenditure index results, which normalize the energy expenditure for each test and describe the relative energy dissipation-recovery behavior of a material, suggested that, for the relatively severe contact strains about a sharp Berkovich indenter, dissipation dominates the mechanical response of both the hydrated and dry dentin. In support of our initial hypothesis, dry dentin presented a significantly higher energy expenditure index than hydrated dentin (p<0.0001). These results were primarily associated with a lower U(e) that was found upon drying. Hydration also decreased H significantly (p<0.0001). In summary, this study presents the first direct measurements of the energy expenditure behavior of hydrated and dry dentin using instrumented nanoindentation.
Publisher: IOP Publishing
Date: 21-10-1976
Publisher: Elsevier BV
Date: 06-2010
DOI: 10.1016/J.DENTAL.2010.02.002
Abstract: The metastability of the tetragonal crystal structure of yttria partial stabilized zirconia polycrystalline (Y-TZP) ceramics is a basis of concern for dental restorations. Reactions between the porcelain and the Y-TZP framework may result in a reduction of the stability of the zirconia and interface bonding caused by a transformation from tetragonal to monoclinic crystalline structure during veneering. XRD(2) micro-diffraction measurements were carried out on tapered veneered cross-sections of the interface area to generate locally resolved information of the phase content in this region. To get a high intensity X-ray beam for short measurement times a focussing polycapillary with a spot size of app. 50 microm was used to evaluate the porcelain zirconia interface. Under almost all conditions the phase composition of zirconia grains at the interface revealed both the monoclinic and tetragonal structure. These observations indicate that destabilization of the tetragonal phase of zirconia occurs at the interface during veneering with porcelain. These results and their relevance to the long-term stability of the interface adhesion between zirconia and veneering porcelain as well as the tetragonal to monoclinic crystal transformations at the interface are discussed.
Publisher: IOP Publishing
Date: 06-2010
Publisher: Elsevier BV
Date: 05-2007
Publisher: Elsevier BV
Date: 12-2003
Publisher: Elsevier BV
Date: 03-2016
DOI: 10.1016/J.DENTAL.2015.11.018
Abstract: This study aimed to in idually quantify the effects of various design parameters, including margin thickness, convergence angle of abutment, and bonding conditions on fracture resistance of resin bonded glass dental crown systems (namely, glass simulated crown). An in vitro experimental test and an in silico computational eXtended Finite Element Method (XFEM) were adopted to explore crack initiation and propagation in glass simulated crown models with the margin thickness ranging from 0.8 to 1.2mm, convergence angle from 6° to 12°, and three different bonding conditions, namely non-bonded (NB), partially bonded (PB), fully bonded (FB). The XFEM modeling results of cracking initiation loads and subsequent growth in the glass simulated crown models were correlated with the experimental results. It was found that the margin thickness has a more significant effect on the fracture resistance than the convergence angle. The adhesively bonded state has the highest fracture resistance among these three different bonding conditions. Crowns with thicker margins, smaller convergence angle and fully bonded are recommended for increasing fracture resistance of all-ceramic crowns. This numerical modeling study, supported by the experimental tests, provides more thorough mechanical insight into the role of margin design parameters, thereby forming a novel basis for clinical guidance as to preparation of tapered abutments for all-ceramic dental crowns.
Publisher: Elsevier BV
Date: 12-2018
DOI: 10.1016/J.DENTAL.2018.09.002
Abstract: This in-vitro study aimed to develop a technique to measure the frictional forces and determine the frictional coefficient (μ) associated with the rubbing of dental floss against teeth. Incorrect flossing technique and the etiology of grooves at the cementoenamel junction (CEJ) of proximal area of teeth has long been a controversial topic. We hypothesized that the μ between teeth surfaces and dental floss is affected by contact angulation. Tests were conducted using two different types of dental floss (waxed and unwaxed nylon) on different surfaces (enamel, dentine, smooth and rough glass rods) under different moisture conditions (dry and wet). The μ generated by performing C-shape flossing was measured, using the Capstan equation, at constant load (100g) over different flossing contact sliding angulations. In addition, the surface characteristics of intact and used nylon flosses were compared using a scanning electron microscope (SEM). The mean μ was highest with a smooth glass rod (0.42±0.11), followed by rough glass rods (0.30±0.07), dry enamel (0.27±0.08), wet enamel (0.23±0.06), then dentine (0.18±0.04). Moreover, higher μ was associated with waxed floss when used against dry enamel, smooth and rough glass rods (P<0.001). At different moisture conditions, waxed floss demonstrated greater μ with dry surfaces (P<0.03). No association was found between μ and dental floss contact angulation. Both floss types showed deterioration after usage although waxed type exhibited markedly greater deterioration when used on dry surfaces. In conclusion, the magnitude of the μ was found to be influenced by surface roughness, moisture condition, and independent of the contact angulation area during sliding of dental floss. It is important to consider the potential side effects of frictional forces on both tooth surface and dental floss during clinical application.
Publisher: The Optical Society
Date: 13-01-2011
DOI: 10.1364/BOE.2.000345
Publisher: Elsevier BV
Date: 2009
Publisher: Elsevier BV
Date: 06-2010
DOI: 10.1016/J.JBIOMECH.2010.02.016
Abstract: Fixed partial dentures (FPD) or dental bridges have been extensively utilised in prosthodontic restoration. Despite considerable clinical success to date, there has been limited fundamental understanding of the biomechanical consequences induced by FPD treatment. It is noted that FPD construction significantly alters the biological and mechanical environment in the supporting bone region. Thus, the surrounding bones will be engaged to adapt to such a biomechanical change. This paper aims to address this critical issue by developing a new remodelling procedure induced by FPD restoration. Specifically, it relates the mechanical stimulus to the change in Hounsfield Unit (HU) value in terms of surface area density (SAD) of bony morphology, which allows direct correlation to clinical computerised tomography (CT) data. The procedure will provide prosthodontist with a new approach for assessing FPD treatment, thereby optimising FPD design for improving longevity and reliability of future FPD restoration.
Publisher: S. Karger AG
Date: 2003
DOI: 10.1159/000070448
Abstract: The aim of this study was to measure the change in hardness and modulus of elasticity of enamel and dentine in primary teeth using the ultra-micro-indentation system (UMIS) after exposure to potentially erosive beverages and to relate the changes to the chemical composition of the test beverages. Primary molar teeth were sectioned and polished. Indentations were made in enamel and dentine prior to and then after exposure to one of four beverages: distilled water (control), orange juice, Orange Cordial, Fanta sup ® /sup and a ‘toothfriendly’ Tropical Orange Cordial (Ribena sup ® /sup ). Each beverage was then analysed. Fanta and Orange Cordial were the only test beverages to show a statistically significant reduction in the enamel hardness in comparison to the control and only Fanta showed a significant reduction in dentine hardness. None of the test beverages significantly reduced the modulus of elasticity of either enamel or dentine. Statistically the pH, phosphate and fluoride concentrations of the beverages were correlated with softening of enamel. Calcium concentration and titratable acidity were correlated with softening of dentine. The UMIS offers another method of measuring the basic mechanical properties of enamel and dentine. This is useful in predicting the erosive potential of substrates. It is likely that the pH, titratable acidity, fluoride, phosphate and calcium content of beverages are all important in determining the potential erosiveness of beverages.
Publisher: Elsevier BV
Date: 08-2001
Publisher: Springer Science and Business Media LLC
Date: 05-2011
DOI: 10.1007/S12024-011-9240-Y
Abstract: Understanding how bone behaves when subjected to ballistic impact is of critical importance for forensic questions, such as the reconstruction of shooting events. Yet the literature addressing microscopic anatomical features of gunshot wounds to different types of bone is sparse. Moreover, a biomechanical framework for describing how the complex architecture of bone affects its failure during such impact is lacking. The aim of this study was to examine the morphological features associated with experimental gunshot wounds in slaughtered pig ribs. We shot the 4th rib of 12 adult pigs with .22 mm subsonic bullets at close range (5 cm) and examined resultant wounds under the light microscope, scanning electron microscope SEM and micro tomograph μCT. In all cases there was a narrow shot channel followed by spall region, with evidence of plastic deformation with burnishing of the surface bone in the former, and brittle fracture around and through in idual Haversian systems in the latter. In all but one case, the entrance wounds were characterized by superficially fractured cortical bone in the form of a well-defined collar, while the exit wounds showed delamination of the periosteum. Inorganic residue was evident in all cases, with electron energy dispersive spectroscopy EDS confirming the presence of carbon, phosphate, lead and calcium. This material appeared to be especially concentrated within the fractured bony collar at the entrance. We conclude that gunshot wounds in flat bones may be morphologically ided into a thin burnished zone at the entry site, and a fracture zone at the exit.
Publisher: Springer Science and Business Media LLC
Date: 05-2001
Abstract: The mechanical deformation of crystalline silicon induced by micro-indentation has been studied. Indentations were made using a variety of loading conditions. The effects on the final deformation microstructure of the load–unload rates and both spherical and pointed (Berkovich) indenters were investigated at maximum loads of up to 250 mN. The mechanically deformed regions were then examined using cross-sectional transmission electron microscopy (XTEM), Raman spectroscopy, and atomic force microscopy. High-pressure phases (Si-XII and Si-III) and amorphous silicon have been identified in the deformation microstructure of both pointed and spherical indentations. Amorphous Si was observed using XTEM in indentations made by the partial load–unload method, which involves a fast pressure release on final unloading. Loading to the same maximum load using the continuous load cycle, with an approximately four times slower final unloading rate, produced a mixture of Si-XII and Si-III. Slip was observed for all loading conditions, regardless of whether the maximum load exceeded that required to induce “pop-in” and occurs on the {111} planes. Phase transformed material was found in the region directly under the indenter which corresponds to the region of greatest hydrostatic pressure for spherical indentation. Slip is thought to be nucleated from the region of high shear stress under the indenter.
Publisher: Elsevier BV
Date: 05-1978
Publisher: Springer Science and Business Media LLC
Date: 15-08-2008
DOI: 10.1007/S10856-007-3154-Y
Abstract: Gelatine sponge because of its flexibility, biocompatibility, and biodegradability, has the potential to be used as a scaffold to support osteoblasts and to promote bone regeneration in defective areas. This study aimed to determine osteoblast proliferation, differentiation, and integration in modified and un-modified gelatine sponges. Three scaffolds were studied: gelatine sponge (Gelfoam), gelatin sponge/mineral (hydroxyapatite) composite, and gelatin sponge olymer (poly-lactide-co-glycolide) composite. 2-D plastic coverslip was used as control. The gelatin sponges were modified using PLGA coating and mineral deposition to increase biodegradation resistance and osteoblast proliferation respectively. The scaffolds were characterized using Scanning Electron Microscopy (SEM) and X-ray diffraction. Cell number (DNA content), cell-replication rate (thymidine assay), and cell differentiation (alkaline phosphatase activity) were measured 24 h, 3 days, and 1, 2, 3 weeks after the osteoblast-like cells were cultured onto the scaffolds. Cell penetration into the sponges was determined using haematoxylin-eosin staining. Both modified and unmodified gelatine sponges demonstrated ability to support cell growth and cells were able to penetrate into the sponge pores. In a comparison of different scaffolds, cell number and cell replication were highest in sponge/hydroxyapatite composite and lowest in sponge/PLGA composite.
Publisher: Elsevier BV
Date: 1997
Publisher: Elsevier BV
Date: 08-1996
Publisher: Elsevier BV
Date: 07-2015
DOI: 10.1016/J.ACTBIO.2015.03.035
Abstract: This study investigated the effect of two bleaching agents, 16% carbamide peroxide (CP) and 35% hydrogen peroxide (HP), on the mechanical properties and protein content of human enamel from freshly extracted teeth. The protein components of control and treated enamel were extracted and examined on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Marked reduction of the protein matrix and random fragmentation of the enamel proteins after bleaching treatments was found. The mechanical properties were analyzed with Vickers indentations to characterize fracture toughness, and nanoindentation to establish enamel hardness, elastic modulus and creep deformation. Results indicate that the hardness and elastic modulus of enamel were significantly reduced after treatment with CP and HP. After bleaching, the creep deformation at maximum load increased and the recovery upon unloading reduced. Crack lengths of CP and HP treated enamel were increased, while fracture toughness decreased. Additionally, the microstructures of fractured and indented s les were examined with field emission gun scanning electron microscopy (FEG-SEM) showing distinct differences in the fracture surface morphology between pre- and post-bleached enamel. In conclusion, tooth bleaching agents can produce detrimental effects on the mechanical properties of enamel, possibly as a consequence of damaging or denaturing of its protein components.
Publisher: AIP Publishing
Date: 10-06-2002
DOI: 10.1063/1.1486264
Abstract: Contact-induced damage has been studied in single-crystal (wurtzite) ZnO by cross-sectional transmission electron microscopy (XTEM) and scanning cathodoluminescence (CL) monochromatic imaging. XTEM reveals that the prime deformation mechanism in ZnO is the nucleation of slip on both the basal and pyramidal planes. Some indication of dislocation pinning was observed on the basal slip planes. No evidence of either a phase transformation or cracking was observed by XTEM in s les loaded up to 50 mN with an ∼4.2 μm radius spherical indenter. CL imaging reveals a quenching of near-gap emission by deformation-produced defects. Both XTEM and CL show that this comparatively soft material exhibits extensive deformation damage and that defects can propagate well beyond the deformed volume under contact. Results of this study have significant implications for the extent of contact-induced damage during fabrication of ZnO-based (opto)electronic devices.
Publisher: Springer Science and Business Media LLC
Date: 26-05-2011
DOI: 10.1007/S10856-011-4350-3
Abstract: Simulation of tooth preparation using rotary cutting instruments is viewed as beneficial and essential in dental training. Various types of materials have been used for simulation systems in dental preclinical training. However, the phantom tooth materials used for simulation have not changed significantly for decades and they are acknowledged to be different from natural teeth. This study investigated the mechanical properties and microstructure of a widely used phantom tooth material and compared them with a novel, polymer infiltrated, ceramic. It was concluded that the polymer infiltrated ceramic has mechanical properties more similar to natural teeth than current phantom tooth materials, suggesting that it might be a good candidate material for phantom teeth for trainees to acquire initial tactile sense for tooth preparation.
Publisher: Elsevier BV
Date: 06-2016
DOI: 10.1016/J.JMBBM.2016.01.035
Abstract: This study aimed to explore the "sensitivity" of the fracture load and initiation site to loading position on the central occlusal surface of a pontic tooth for both all-ceramic inlay retained and onlay supported partial denture systems. Three dimensional (3D) finite element (FE) inlay retained and onlay supported partial denture models were established for simulating crack initiation and propagation by using the eXtended Finite Element Method (XFEM). The models were subjected to a mastication force up to 500N on the central fossa of the pontic. The loading position was varied to investigate its influence on fracture load and crack path. Small perturbation of the loading position caused the fracture load and crack pattern to vary considerably. For the inlay fixed partial dentures (FPDs), the fracture origins changed from the bucco-gingival aspect of the molar embrasure to the premolar embrasure when the indenter force location is slightly shifted from the mesial to distal side. In contrast, for onlay FPDs, cracking initiated from bucco-gingival aspect of the premolar embrasure when the indenter is slightly shifted to the buccal side and from molar embrasure when the indenter is shifted to the lingual side. The fracture load and cracking path were found to be very sensitive to loading position in the all-ceramic inlay and onlay FPDs. The study provides a basis for improved understanding on the role of localized contact loading of the cusp surface in all-ceramic FPDs.
Publisher: Wiley
Date: 06-2011
Publisher: Informa UK Limited
Date: 07-2002
Publisher: Springer Science and Business Media LLC
Date: 03-2006
Abstract: The elastic modulus of an amorphous polymer was investigated by nanoindentation using combinations of ten total penetration depths and three constant unload rates. This experimental design provided a range of unloading strain rates coexisting with a range of depths. The elastic modulus of the material was found to correlate strongly with the unloading strain rate, whereas its correlation with the indentation depth was statistically nonsignificant. Thus, the increase of elastic modulus that occurred with decreasing depth at each constant unload rate was merely due to the increasing unloading strain rate associated with the decreasing depth. The true depth dependence of a rate-dependent material can therefore be studied only by maintaining a constant unloading strain rate across the entire depth range. The implications of these results to the continuous stiffness measurement technique are considered.
Publisher: Wiley
Date: 05-1983
Publisher: Springer Science and Business Media LLC
Date: 02-1994
DOI: 10.1007/BF00446001
Publisher: Elsevier BV
Date: 05-2002
DOI: 10.1016/S0109-5641(01)00084-7
Abstract: The aim of the study was to investigate the mechanical properties and energy absorption behavior of mouth-guard materials. Interpretation of indentation force-displacement data has been used to determine these properties. An ultra micro-indentation system (UMIS) was used to determine near surface properties of mouth-guard materials with nanometer and micro-Newton displacement and force resolution. The measurement procedure was conducted with a small spherical steel indenter (R=500 microm), with impressions that were equally spaced (250 microm). Measurements of force-displacement response of surfaces at maximum forces of 10, 40 or 50 mN, 10 indentations were made at each of these forces. Tests were undertaken in two different modes to determine the mechanical properties, namely: (a) continuous load to the maximum force and then unload, (b) multiple loading and partially unloading sequence to the maximum load. The force-displacement results were analysed to determine the elastic modulus and contact pressure versus depth of penetration as well as the energy loss. Energy absorption for each material was determined from the ratio of the hysteresis energy loss to the total energy at maximum load and ranged from 10 to 24% among different mouth-guard materials. Energy absorption ratio, elastic modulus and contact pressure were significantly different between different materials with same thickness (FC, GC and C3) (p<0.01) and significantly different between materials with different thickness (C1 and C3) (p<0.01). The present approach provides a simple and efficient method to readily measure the elastic-plastic (hysteretic) response of mouth-guard materials. The indentation technique lends itself to investigate the influence of ageing, heat treatment, sterilisation, moisture etc in a simple systematic manner.
Publisher: Public Library of Science (PLoS)
Date: 15-03-2013
Publisher: Elsevier BV
Date: 1992
Publisher: Elsevier BV
Date: 09-2017
DOI: 10.1016/J.DENTAL.2017.06.007
Abstract: To quantify the adhesion of two bonding approaches of zirconia to more aesthetic glass-ceramic materials using the Schwickerath (ISO 9693-2:2016) three point bend (3PB) [1] test to determine the fracture initiation strength and strain energy release rate associated with stable crack extension with this test and the Charalamabides et al. (1989) [2] four point bend (4PB) test. Two glass-ceramic materials (VITABLOCS Triluxe forte, Vita Zahnfabrik, Germany and IPS.emax CAD, Ivoclar Vivadent, Liechtenstein) were bonded to sintered zirconia (VITA InCeram YZ). The former was resin bonded using a dual-cure composite resin (Panavia F 2.0, Kuraray Medical Inc., Osaka, Japan) following etching and silane conditioning, while the IPS.emax CAD was glass bonded (IPS e.max CAD Crystall/Connect) during crystallization of the IPS.emax CAD. Specimens (30) of the appropriate dimensions were fabricated for the Schwickerath 3PB and 4PB tests. Strength values were determined from crack initiation while strain energy release rate values were determined from the minima in the force-displacement curves with the 3PB test (Schneider and Swain, 2015) [3] and for 4PB test from the plateau region of stable crack extension. Strength values for the resin and glass bonded glass ceramics to zirconia were 22.20±6.72MPa and 27.02±3.49MPa respectively. The strain energy release rates for the two methods used were very similar and for the glass bonding, (4PB) 15.14±5.06N/m (or J/m The present results indicate 3PB and 4PB tests have very similar values for the strain energy release rate determination. However while strength tests reveal minimal differences between resin and glass bonding, strain energy release rates for the latter are superior for bonding CAD/CAM milled glass-ceramics to zirconia.
Publisher: Wiley
Date: 14-06-2010
DOI: 10.1111/J.1365-2842.2010.02113.X
Abstract: The aim of this study is to review all the published literature investigating the accuracy of fit of zirconia fixed partial dentures (FPD). A comprehensive electronic search was performed through PubMed (MEDLINE) using Boolean operators to combine the following key words: 'zirconia,''margin,''FPD,''internal,''fit,''gap,''fitting surface,''bridge' and 'fixed prosthesis.' The search was limited to articles written in English, published up to January 2010. In addition, a manual search was also conducted through articles and reference lists retrieved from the electronic search and peer-reviewed journals. A total of 115 articles were retrieved and only 15 met the specified inclusion criteria for the review. Twelve of these articles were in vitro and three of them were in vivo. The selected articles had assessed marginal and/or internal fit of zirconia FPDs against the effect of various parameters that were computer-aided design and computer-aided manufacturing (CAD/CAM) and CAM systems, post-sintered and pre-sintered milling, framework configuration, span length, veneer application and ageing. CAD/CAM, post-sintered milling, straight configuration and shorter span frameworks provided superior results than CAM, pre-sintered milling, curved configuration and longer span frameworks. Veneering zirconia frameworks caused deterioration in fit, while ageing of zirconia had no implications on the fit. Further studies are needed to determine the clinical significance of the differences in the accuracy reported in this review.
Publisher: Wiley
Date: 27-09-2014
DOI: 10.1111/ADJ.12218
Abstract: The current study objectives were to evaluate the influence of fluoridated glass fillers loading on the surface roughness, wettability, and adherence of candida and bacteria with and without saliva presence to a polymethylmethacrylate (PMMA) denture base material surface. Four concentrations of fluoridated glass fillers were added to PMMA: 1%, 2.5%, 5% and 10% by weight pre-polymerization and 0% was the control. Discs of each concentration were fabricated (n = 5 for each variable). Surface roughness (Ra ) was measured using atomic force microscopy (AFM). Wettability was assessed by measuring the contact angle of a sessile drop of water. Specimens were incubated with Candida albicans, or Streptococcus mutans with and without saliva coating. Adherence was presented as a percentage of the colonized surface area, counted using an optical microscope at x100 magnification. The 10% group showed significantly greater roughness than the control and 1% groups however, no significant differences in contact angle values were detected. The microbial adhesion was inversely proportional to the fluoridated glass fillers concentration where 10% concentration significantly decreased candidal and bacterial adhesion compared to others. Saliva coating significantly decreased microbial adhesion. It was concluded that fluoridated glass fillers could decrease microbial adhesion to acrylic denture base without adversely affecting surface properties.
Publisher: Wiley
Date: 16-07-2004
Publisher: Elsevier BV
Date: 04-1988
Publisher: Springer Science and Business Media LLC
Date: 07-1986
DOI: 10.1038/322234A0
Publisher: SPIE
Date: 21-11-2017
DOI: 10.1117/12.2307996
Publisher: Springer Science and Business Media LLC
Date: 2000
Publisher: Wiley
Date: 2001
DOI: 10.1002/1097-4636(2001)58:2<188::AID-JBM1006>3.0.CO;2-V
Abstract: Accurate determination of the elastic modulus of surgical bone cements is of primary importance, when evaluating the stresses within the cement mantle in Total Joint Arthroplasty. This article presents a new method of determining the modulus of surgical bone cements from the biaxial flexural test. The biaxial flexural test is not currently employed in mainstream orthopedic mechanical testing, which is surprising because most loading in orthopedic applications is biaxial in nature. Nor has this method been utilized for dental materials, even though the biaxial flexure test has been used for many years in this field. It has been demonstrated that the modulus of surgical bone cements can be determined from the biaxial flexural test, and these results are in agreement with results from compressive and bending tests.
Publisher: Elsevier BV
Date: 10-2013
DOI: 10.1016/J.JMBBM.2013.05.004
Abstract: To determine the flexural strength and subsequent strength degradation of a range of dental CAD/CAM ceramic materials and novel PICN (Polymer-Infiltrated-Ceramic-Network) materials by means of pre-damaging with Vickers indentations at various loads. The materials tested included (Mark II, PICN test material 1 and 2, In-Ceram Alumina, VM 9, In-Ceram YZ Vita Zahnfabrik, Bad Saeckingen, Germany) and (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein). Bending bars were cut and lapped with 15 µm diamond suspension. Initial flexural strength (n=10) was determined in three-point-bending. To evaluate the damage tolerance, Vickers indentations were placed on the bending bars (n=35) with varying loads (1.96-98.07 N). The indented bending bars were subsequently loaded to fracture in three-point-bending. In addition, the fracture toughness was determined by the indentation strength (IS) and the SEVNB technique (n=5). With increasing indentation loads the fracture strength of all materials tested decreased. The material with the highest fracture resistance to indentation induced damage, was the PICN test material 1 with an indentation load-flexural strength curve slope of 0.21. In-Ceram YZ exhibited the highest damage susceptibility with a slope of 0.4. The fracture toughness varied with the measurement technique and material in the range of 0.82 (VM 9) to 4.94 (In-Ceram YZ) MPa√m for the SEVNB method and 0.96 (VM 9) to 4.97 (In-Ceram YZ) MPa√m for the IS method respectively. This study aims to indicate the likely clinical behavior by evaluating the damage tolerance and R-curve behavior of dental ceramics by in-vitro strength degradation and fracture toughness measurements.
Publisher: Elsevier BV
Date: 06-2007
Publisher: AIP Publishing
Date: 07-2005
DOI: 10.1063/1.1992663
Publisher: Springer Science and Business Media LLC
Date: 2005
DOI: 10.1007/S10856-005-5995-6
Abstract: Electrophoretic deposition (EPD) is a low cost flexible process for producing HA coatings on metal implants. Its main limitation is that it requires heating the coated implant in order to densify the HA. HA typically sinters at a temperature below 1150 degrees C, but metal implants are degraded above 1000 degrees C. Further, the metal induces the decomposition of the HA coating upon sintering. Recent developments have enabled EPD of metathesis-synthesised uncalcined HA which sinters at approximately 1000 degrees C. The effects of temperature on HA-coated Ti, Ti6Al4V, and 316L stainless steel were investigated for dual coatings of metathesis HA sintered at 1000 degrees C. The use of dual HA coatings (coat, sinter, coat, sinter) enabled decomposition to be confined to the "undercoat" (HA layer 1), with the surface coating decomposition free. The tensile strength of the three metals was not significantly affected by the high sintering temperatures (925 degrees C < T 10 microm) comprising a TiO2 oxidation zone and a CaTiO2 reaction zone.
Publisher: Springer Science and Business Media LLC
Date: 06-2008
Abstract: A viscoelastic solid was contacted by a pointed indenter using low-frequency large- litude sinusoidal load functions to determine its contact stiffness in a manner similar to that of the continuous stiffness measurement (CSM) technique but in a quasi-static condition. The contact stiffness of a viscoelastic solid determined by the CSM technique, or the dynamic stiffness, is known, from previous CSM-based studies, to overestimate the quasi-static contact stiffness. The contact stiffness of a viscoelastic solid determined in a quasi-static manner is thus hypothesized to help predict the contact depth more accurately. A new analysis procedure based on truncated Fourier series fitting was developed specifically to process the large litude sinusoidal indentation data. The elastic modulus of the material characterized in this work was in agreement with that determined by dynamic mechanical analysis, thereby providing evidence for the validity of the present method in characterizing other viscoelastic materials.
Publisher: Elsevier BV
Date: 03-2005
Publisher: Elsevier BV
Date: 02-2013
Publisher: Wiley
Date: 12-2013
DOI: 10.1111/ADJ.12107
Abstract: This study is the last in a series detailing an investigation into the all-ceramic, inlay supported fixed partial denture, the major concern of which has been the examination of the stress responses of the bridge via the use of finite element analysis (FEA) and its validation. The progression from a classic FEA to the current extended or enriched FEA (XFEA) will be described and the validation performed. XFEA modelling was compared and validated against the experimental model analysis (EMA) as described in a previous study. The two EMA load case fracture strengths of 160 N and 313 N compared favourably with the best two fracture predictions from the XFEA of 185 N and 213 N (maximum principal stress criterion) respectively, with the origin of fracture and overall trajectory and pattern of crack propagation agreeing very well. XFEA load prediction is within 15% of the EMA in the best case. The sensitivity of the bridges to loading position variations was accurately predicted by the XFEA, together with the change in fracture origin from the molar to premolar embrasures. With this, the authors believe that they have provided a convincing validation, both qualitatively and quantitatively, of an anatomically realistic dental bridge.
Publisher: Elsevier BV
Date: 02-2012
DOI: 10.1016/J.DENTAL.2011.11.012
Abstract: The reliability and longevity of ceramic prostheses have become a major concern. The existing studies have focused on some critical issues from clinical perspectives, but more researches are needed to address fundamental sciences and fabrication issues to ensure the longevity and durability of ceramic prostheses. The aim of this paper was to explore how "sensitive" the thermal and mechanical responses, in terms of changes in temperature and thermal residual stress of the bi-layered ceramic systems and crown models will be with respect to the perturbation of the design variables chosen (e.g. layer thickness and heat transfer coefficient) in a quantitative way. In this study, three bi-layered ceramic models with different geometries are considered: (i) a simple bi-layered plate, (ii) a simple bi-layer triangle, and (iii) an axisymmetric bi-layered crown. The layer thickness and convective heat transfer coefficient (or cooling rate) seem to be more sensitive for the porcelain fused on zirconia substrate models. The resultant sensitivities indicate a critical importance of the heat transfer coefficient and thickness ratio of core to veneer on the temperature distributions and residual stresses in each model. The findings provide a quantitative basis for assessing the effects of fabrication uncertainties and optimizing the design of ceramic prostheses.
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.DENTAL.2011.06.009
Abstract: To provide a brief summary of the background theory of interfacial fracture mechanics and develop an analytical framework that identifies the critical factors for the analysis of the initiation and propagation of adhesion failure in composite restorations. A conceptual framework utilizing interfacial fracture mechanics and Toya's solution for a partially delaminated circular inclusion in an elastic matrix, which can be applied (with caution) to approximate polymer curing induced cracking about composite resins for class 1 cavity restorations. The findings indicate that: (1) most traditional shear tests are not appropriate for the analysis of the interfacial failure initiation (2) material properties of the restorative and tooth material have a strong influence on the energy realize rate (3) there is a strong size effect and (4) interfacial failure once initiated is characterized by unstable propagation along the interface almost completely encircling the composite. The work is important for the analysis of the reliability of composite class I restorations and provides an adequate interpretation of recent adhesion debonding experimental results utilizing tubular geometry of specimens. The approach clearly identifies the critical parameters including curing strain, material modulii, size and interfacial strain energy release rate for reliable development of advanced restorative materials.
Publisher: Elsevier BV
Date: 06-2001
DOI: 10.1016/S0142-9612(00)00324-0
Abstract: Frequently, bone cement strengths are evaluated from uniaxial tests, such as three- or four-point flexure. Measurement of material strength in this manner may not provide an accurate characterisation of a bone cements true load-bearing capacity. In most orthopaedic applications, there exists a state of biaxial stress and so biaxial strength information is most useful. To address this issue, the biaxial flexure strength of two polymethylmethacrylate orthopaedic (PMMA) bone cements and two glass-ionomer dental cements have been determined. The biaxial strength of orthopaedic bone cements have been compared to the three-point bending strength. Furthermore, the calculated theoretical biaxial strength was compared with a value of biaxial strength utilising the finite element method. For all materials tested the calculated biaxial strength is significantly greater than the three-point bending strength. The biaxial test offers several advantages over three-point bending because it critically explores surface flaws--as it does not matter in which orientation the crack lies. However, it does minimise the volume or surface area investigated and also the edge effect. The difference in strength calculated for the two testing methods can be explained quantitatively in terms of the volume of material under stress. This work has demonstrated that the biaxial flexure test can be used for the testing of orthopaedic bone cements.
Publisher: Elsevier BV
Date: 08-2010
DOI: 10.1016/J.DENTAL.2010.04.004
Abstract: This study evaluated the effect of a chromium interlayer deposited by electroplating on the shear bond strength between titanium and porcelain. Seventy specimens of machined commercially pure titanium (CP Ti) plates grade II (10 mm x 10 mm x 1 mm) were prepared. The specimens were ided into three groups according to the concentration of electroplating solution, Gr I (control without electroplating, n=10), Gr II (5%, w/v, of chromium nitrate solution, n=30) and Gr III (10%, w/v, of chromium nitrate solution, n=30). Groups II and III were further ided into three subgroups (n=10) according to the electroplating time (0.5, 1 and 2 h). Two titanium-porcelains (Vita Titankeramik and Triceram) were applied to each subgroup (n=5). The titanium-porcelain interfaces were loaded under shear in a universal testing machine (crosshead speed: 0.5 mm/min) until failure occurred. Failure types were examined with stereomicroscope and the titanium-porcelain interface examined by SEM. Data were analyzed using ANOVA and Tukey's test. Bond strength values were significantly affected by the type of electroplating treatment (P 0.05). The CP Ti/Vita Titankeramik (0.5 h, 10%, w/v) and the CP Ti/Triceram (0.5h 5%, w/v) groups showed the highest bond strength (MPa) (26.72+/-5.78 and 25.48+/-4.14) respectively among the groups. Stereomicroscope and SEM images showed that chromium interlayer enhanced the bond strength between porcelain and titanium. Bond strength between porcelain and CP Ti can be improved by the use of chromium interlayer prior to porcelain firing.
Publisher: Elsevier BV
Date: 04-2010
DOI: 10.1016/J.JDENT.2009.11.009
Abstract: This in vitro study evaluated the effects of a zinc oxide eugenol (ZOE) base on the mechanical properties of a composite resin restoration. Class I cavities were prepared on plastic teeth and filled with ZOE plus composite resin, following standard clinical procedures. The s les were sectioned sagittally and the ZOE-resin interface was exposed. After polishing, nanoindentation was performed on the region near the interface, and elastic modulus and hardness were plotted in the form of a color contour map. SEM was employed to observe the interface between composite resin and ZOE base. In the region close to the ZOE base, the elastic modulus and hardness of composite resin reduced to the values of 9.71+/-0.54 and 0.51+/-0.05 GPa, respectively. Eugenol from ZOE had detrimental effects on the composite resin only to a distance of less than 100 microm from the ZOE base. Although eugenol suppresses polymerization slightly, by considering the biological advantages of ZOE, together with the results of the current investigation, ZOE may still be considered a suitable base material for composite resin. Bonding is essential for composite resin restorations over ZOE bases to avoid shrinkage detachment.
Publisher: Elsevier BV
Date: 06-2013
DOI: 10.1016/J.ARCHORALBIO.2012.09.017
Abstract: Caries lesions in dental hard tissues autofluoresce when exposed to light of certain wavelengths, whereas sound tissues do not, and this can be used as an in vitro histological marker for dental caries. Detection of autofluorescence is the basis of KaVo DIAGNOdent™ technology, and provides objective feedback control of laser-stimulated ablation of dental caries for the KaVo Key Laser 3™. This Er:YAG laser operates at 2940nm wavelength, and is effective at removal of infected dental hard tissues. Micro-computed tomography (micro-CT) allows the non-invasive investigation of three-dimensional structures and analysis of mineral density profiles of dentine following laser ablation. To evaluate removal of infected, demineralised dentine by Er:YAG irradiation with a laser feedback mechanism, using micro-CT. 27 carious teeth (1 control) and 1 sound tooth, treated with the KaVo Key Laser 3™ using a KaVo™ non-contact 2060 handpiece at specific feedback settings, were examined using a Skyscan 1172 Micro-CT, to observe the efficiency of demineralised dentine removal. Grey scale images obtained were colour rendered to assist detection of demineralised tissue if present. Complete removal of demineralised tissue occurred with laser-stimulated ablation under feedback control at values of 7 and 8 when measured by micro-CT. At greater values, removal of demineralised dentine was incomplete. Examination of dental tissues by micro-CT allowed determination of the efficiency of Er:YAG laser-stimulated ablation. Feedback control of the KaVo Key Laser 3™ appeared to operate like a cut-off switch when infected dentine was eliminated, at a threshold of between 6 and 7.
Publisher: Elsevier BV
Date: 04-1999
Publisher: AIP Publishing
Date: 15-02-2007
DOI: 10.1063/1.2490563
Abstract: Sudden excursions of unusually large magnitude (& μm), “giant pop-ins,” have been observed in the force-displacement curve for high load indentation of crystalline germanium (Ge). A range of techniques including Raman microspectroscopy, focused ion-beam cross sectioning, and transmission electron microscopy, are applied to study this phenomenon. Amorphous material is observed in residual indents following the giant pop-in. The giant pop-in is shown to be a material removal event, triggered by the development of shallow lateral cracks adjacent to the indent. Enhanced depth recovery, or “elbowing,” observed in the force-displacement curve following the giant pop-in is explained in terms of a compliant response of plates of material around the indent detached by lateral cracking. The possible causes of amorphization are discussed, and the implications in light of earlier indentation studies of Ge are considered.
Publisher: Springer Science and Business Media LLC
Date: 11-09-2015
DOI: 10.1007/S10237-014-0612-6
Abstract: This paper explores the biomechanics and associated bone remodeling responses of two different abutment configurations, namely implant-implant-supported versus tooth-implant-supported fixed partial dentures. Two 3D finite element analysis models are created based upon computerized tomography data. The strain energy density induced by occlusal loading is used as a mechanical stimulus for driving the bone remodeling. To measure osseointegration and stability during healing, a resonance frequency analysis is conducted. At the second premolar peri-implant region, overloading resorption around the neck of implant is identified in both the models over the first 12 months. Stress-shielding around the edentulous region is also observed in both the models with a greater resorption rate found in the implant-implant case. The remodeling and resonance frequency analyses reveal that the tooth-implant scheme offers a higher degree of osseointegration. The remodeling procedure is expected to provide prosthodontists with a modeling tool to assess possible long-term clinical outcomes.
Publisher: Elsevier BV
Date: 2012
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.JMBBM.2014.07.024
Abstract: Dental enamel - a naturally occurring biocomposite of mineral and protein - has evolved from a simple prismless to an advanced prismatic structure over millions of years. Exploring the mechanical function of its structural features with differing characteristics is of great importance for evolutionary developmental studies as well as for material scientists seeking to model the mechanical performance of biological materials. In this study, mechanical properties of prismless tuatara Sphenodon punctatus enamel were characterized. Using micro-cantilever bending s les the fracture strength and elastic modulus were found to be 640 ± 87 MPa and 42 ± 6 GPa, respectively in the orientation parallel to the crystallite long axis, which decreased in the orthogonal direction. The intrinsic fracture toughness of tuatara enamel ranged from 0.21 MPa m(1/2) and 0.32 MPa m(1/2). These values correspond to the lower limit of the range of values observed in prismatic enamel at the hierarchical level 1.
Publisher: Wiley
Date: 09-2004
Publisher: AIP Publishing
Date: 06-12-2004
DOI: 10.1063/1.1832757
Abstract: The deformation behavior of self-ion-implanted amorphous-Si (a-Si) has been studied using spherical nanoindentation in both relaxed (annealed) and unrelaxed (as-implanted) a-Si. Interestingly, phase transformations were clearly observed in the relaxed state, with the load–unload curves from these s les displaying characteristic discontinuities and cross-sectional transmission electron microscopy images indicating the presence of high-pressure crystalline phases Si-III and Si-XII following pressure release. Thus, an amorphous to crystalline phase transformation has been induced by indentation at room temperature. In contrast, no evidence of a phase transformation was observed in unrelaxed a-Si, which appeared to deform via plastic flow of the amorphous phase. Furthermore, in situ electrical measurements clearly indicate the presence of a metallic Si phase during loading of relaxed a-Si but no such behavior was observed for unrelaxed a-Si
Publisher: Elsevier BV
Date: 04-2003
DOI: 10.1067/MPR.2003.42
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 03-2000
Publisher: Springer Science and Business Media LLC
Date: 09-1994
DOI: 10.1007/BF00376271
Publisher: Elsevier BV
Date: 2008
DOI: 10.1016/J.JMBBM.2007.05.001
Abstract: As the hardest and one of the most durable load-bearing tissues of the body, enamel has attracted considerable interest from both material scientists and clinical practitioners due to its excellent mechanical properties. In this paper, possible mechanisms responsible for the excellent mechanical properties of enamel are explored and summarized, which primarily include its hierarchical structure and the nanomechanical properties of the minor protein macromolecular component. Furthermore, additional experimental and numerical evidences to support the assumptions are presented. For ex le, enamel shows lower elastic modulus, higher energy absorption ability and greater indentation creep behaviour than sintered hydroxyapatite material. All the data indicate that the structural and compositional characteristics of the minor protein component significantly regulate the mechanical properties of enamel to better match its functional needs.
Publisher: Wiley
Date: 24-05-2004
Publisher: Elsevier BV
Date: 03-2010
DOI: 10.1016/J.BIOMATERIALS.2009.11.045
Abstract: The microstructure of enamel like most biological tissues has a hierarchical structure which determines their mechanical behavior. However, current studies of the mechanical behavior of enamel lack a systematic investigation of these hierarchical length scales. In this study, we performed macroscopic uni-axial compression tests and the spherical indentation with different indenter radii to probe enamel's elastic/inelastic transition over four hierarchical length scales, namely: 'bulk enamel' (mm), 'multiple-rod' (10's microm), 'intra-rod' (100's nm with multiple crystallites) and finally 'single-crystallite' (10's nm with an area of approximately one hydroxyapatite crystallite). The enamel's elastic/inelastic transitions were observed at 0.4-17 GPa depending on the length scale and were compared with the values of synthetic hydroxyapatite crystallites. The elastic limit of a material is important as it provides insights into the deformability of the material before fracture. At the smallest investigated length scale (contact radius approximately 20 nm), elastic limit is followed by plastic deformation. At the largest investigated length scale (contact size approximately 2 mm), only elastic then micro-crack induced response was observed. A map of elastic/inelastic regions of enamel from millimeter to nanometer length scale is presented. Possible underlying mechanisms are also discussed.
Publisher: Elsevier BV
Date: 02-2018
Publisher: Wiley
Date: 02-08-2013
DOI: 10.1111/J.1600-0501.2012.02566.X
Abstract: The aim of this study was to evaluate a new method to quantify longitudinal mandibular bone remodeling three-dimensionally by superimposition of cone beam computed tomography images. This method is used to quantify the treatment effects of implant-retained overdentures in 20 patients aged 52-79 at recruitment after 1 and 2 years post treatment. Three dimensional models of pre- and post-treatment were reconstructed for each patient and superimposed using Standard Tessellation Language registration method and segmentation. Color maps of the differences generated by superimposition allow detailed examination and quantification of the progressive dimensional changes of bone in a three-dimensional manner and enable the visualization of the apical displacement and thinning of the cortical layer of bone underneath the denture base. Most of the remodeling changes took place during the first year with a mean decrease in volume of 3.7% (SD = 4.4% range = +3.7% to -15.9%, median = -3.7%). This remodeling pattern continued during the second year, but at a reduced rate of 2.5% per year (SD = 4.2% range = +2.1% to -11.3%, median = -3.9%). Standard Tessellation Language registration based superimposition of cone beam computed tomography images may be considered an objective and reproducible method to three-dimensionally quantify mandibular bone remodeling.
Publisher: Oxford University Press (OUP)
Date: 18-10-2010
DOI: 10.1093/EJO/CJQ103
Abstract: This study compared the moments produced by V-bends placed in rectangular nickel titanium (NiTi) orthodontic wire to those produced in titanium-molybdenum alloy (TMA). V-bends that included angles of 135, 150, and 165 degrees were heat set into 0.017×0.025 and 0.016×0.025 inch NiTi alloy wires and identical bends bent into TMA wires with a dimension of 0.018×0.025 and 0.016×0.022 inch. There were five specimens per group (N=60). The moments produced by each specimen were tested on a custom jig that aligned two lower incisor brackets with zero tip or torque at an interbracket distance of 15 mm. The upper bracket was connected to a moment transducer. The V-bend position for each specimen was varied in 1 mm increments towards the moment transducer. The moments produced by TMA wires were linear, which increased as the V-bend approached the transducer, while NiTi exhibited a non-linear curve characterized by a flattening of the moment value. The point of dissociation (where the moment experienced by the bracket became zero) was estimated for both wire types using linear mixed model analysis. For TMA wires, this point was similar to that reported in the literature but was significantly less for NiTi wire when compared with TMA. The moments produced by TMA generally increased with the magnitude of the V-bend, whereas this was not the case for NiTi.
Publisher: Elsevier BV
Date: 09-2009
Publisher: Trans Tech Publications Ltd.
Date: 15-06-2006
Publisher: Elsevier BV
Date: 07-2014
DOI: 10.1016/J.PROSDENT.2013.08.012
Abstract: The human mandible flexes during different jaw movements. Mandibular flexure is known to be restricted when natural dentition is restored with long-span fixed prostheses, but its effect on implant-supported fixed prostheses is unknown. Restriction of mandibular movement by implant-supported fixed prostheses may lead to excess strain accumulation, which could affect the outcome of implant treatment. The purpose of this study was to investigate the influence of mandibular flexure on the implant bone interface by measuring the strain distribution in the body of the mandible at the periimplant level and at the implant framework level during the unilateral loading of a long-span implant-supported fixed prosthesis. A partially edentulous mandible model with the mandibular left premolars and molars missing was fabricated in epoxy resin. Two implants were placed in the edentulous area, one in the position of the first premolar and one in the position of the second molar. Strain gauges were cemented at the implant bone interface parallel to each implant on the body of the mandible and on the framework. Three screw-retained, 3 × 3-mm bar-shaped frameworks were cast from cobalt-chromium alloy. The fit of these frameworks was deemed clinically acceptable with a routine clinical assessment technique. The mandible model was suspended by elastic cords to a universal testing machine. A 50-N load cell was placed on the occlusal surface of the right first molar. The mandible model was then loaded to 50 N on the working side first without any framework and then a second time with the framework in place. Information from the strain gauges were collected with a computer for analysis. When the mandible model was loaded without the implant framework, the buccal aspect of the body of the mandible experienced mainly compression, whereas the lingual aspect was mainly in tension on the working side under unilateral loading. At the implant-bone interface, compression strain was detected on the mesial aspect of the mesial implant. When frameworks were placed and a unilateral load applied, compression was detected on the mesial and buccal aspect of the mesial implant with all 3 frameworks. The amount of strain recorded was higher than that recorded without any framework in place. Mandibular flexure occurred during unilateral loading. The amount of strain transmitted to the implants increased with the screw-retained fixed-implant frameworks in place. The amount of strain introduced by mandibular flexure under unilateral loading may not be enough to stimulate bone remodeling however, the accumulative strain generated by mandibular flexure under cyclic loading and its relationship with bone remodeling is unclear.
Publisher: Elsevier BV
Date: 09-2003
DOI: 10.1016/S0300-5712(03)00071-X
Abstract: The objectives of the study were to determine the adhesion at the titanium-porcelain interface using a fracture mechanics approach, and to investigate the bonding mechanism using SEM and X-ray microanalysis. Specimens of four titanium-porcelain bonding systems were prepared in a rectangular shape for a four-point bending test on a universal testing machine. The pre-cracked specimen was subjected to a limited number of load and partial unload cycles, and the strain energy release rate or interfacial toughness (G(c) value) was calculated for each system. The interface was investigated in an SEM, which also enabled quantitative X-ray microanalysis, and comparison with a simulation of an atomically sharp interface to ascertain whether diffusion bonding occurred. The Titanium/Titankeramik with GoldBonder bonding system showed the highest G(c) value (48.9+/-12.4 J/m(2)) among the groups whilst Titanium/Duceratin showed the lowest (12.9+/-3.6 J/m(2)). The former was significantly higher than that of nickel-chromium orcelain (40.3+/-4.8 J/m(2)) from the previous study [Int J Prosthod 12 (1999) 547], which is a clinically accepted bonding system. The G(c) values of Titanium/Titankeramik and Titanium alloy/Titankeramik were 16.7+/-2.4 and 27.8+/-5.3 J/m(2), respectively. The X-ray microanalysis suggested that diffusion of some elements has occurred at the interface. The strain energy release rate (G(c)-value) of titanium/Titankeramik with GoldBonder was highest among the four systems. X-ray microanalysis gave some evidence of diffusion of some elements, particularly of the porcelain into the metal, which may assist the bonding during the firing.
Publisher: Informa UK Limited
Date: 04-2000
Publisher: Hindawi Limited
Date: 2017
DOI: 10.1155/2017/7834905
Abstract: The aim of this study was to investigate the efficacy of various fluoride varnishes in the protection of the structural and nanomechanical properties of dental enamel. Demineralized enamel specimens were imaged using a high-resolution micro-CT system and lesion parameters including mineral density and lesion depth were extracted from mineral density profiles. Nanoindentation elastic modulus and hardness were calculated as a function of penetration depth from the load-displacement curves. The average depth of the lesion in specimens with no prior fluoride varnish treatment was 86 ± 7.1 9 μ m whereas the varnish treated specimens had an average depth of 67 ± 7.03 μ m ( P 0.05 ). The mineral density of enamel lesions with no fluoride varnish treatment had an average of 1.85 gr/cm3 which was 25% lower than the corresponding value in varnish treated enamel and 37% lower than sound enamel. While, in the varnish treated group, elastic modulus and hardness values had decreased by 18% and 23%, respectively, the corresponding values in the non-varnish treated specimens had a reduction of 43% and 54% compared to the sound enamel. The findings from this study highlight the preventive role of fluoride varnishes. Addition of calcium and phosphate does not seem to enhance or inhibit the prevention or remineralization performance of fluoride varnishes.
Publisher: Elsevier BV
Date: 04-2019
DOI: 10.1016/J.DENTAL.2019.01.016
Abstract: To identify the conditions under which fabrication pore defects within veneering porcelain in bilayered lithium disilicate glass-ceramic (LDG) crowns will influence and jeopardize the mechanical integrity of the structure. Thirty standardized molar crowns (IPS e.max Press) were fabricated and microCT scanned to 3D-analyze the size, morphology and distribution of pores in veneering porcelain, followed by in vitro fracture test and SEM fractographic observation. Finite element analysis (FEA) of the microCT reconstructed models was used to evaluate the stress state. The volumes of pores in s les ranged from 3241μm Within the limitation of the microCT resolution and FEA, it suggests that pores radius large than 30-50μm and located in the tensile stress area like grooves and fissures on the occlusal surface or near surface as well as cervical margins of veneering porcelain will jeopardize the bilayered structure and mechanical integrity of LDG.
Publisher: Elsevier BV
Date: 04-2019
DOI: 10.1016/J.DENTAL.2019.01.019
Abstract: To determine the thermal expansion of a porcelain (VM9) and tetragonal zirconia (Y-TZP) as well as the deflection upon re-heating and cooling of a bilayer fabricated from these two materials after slow and rapid cooling during initial fabrication. The coefficient of thermal expansion (CTE) of bulk porcelain and Y-TZP as well as bilayer beam deflection was measured with a novel non-contact optical dilatometer. The influence of cooling rate during initial fabrication of the porcelain-zirconia bilayer and the bulk porcelain during subsequent heating and cooling is investigated. Specimens were heated to 900°C in the dilatometer, well in excess of the glass transition temperature (T The thermal expansion of the porcelain above T The estimation of the residual stress and potential for chipping of porcelain-zirconia dental restorative systems should not be based solely on thermal expansion data measured below T
Publisher: Elsevier BV
Date: 06-2018
DOI: 10.1016/J.MEDENGPHY.2018.03.008
Abstract: Whilst the newly established biomechanical conditions following mandibular reconstruction using fibula free flap can be a critical determinant for achieving favorable bone union, little has been known about their association in a time-dependent fashion. This study evaluated the bone healing/remodeling activity in reconstructed mandible and its influence on jaw biomechanics using CT data, and further quantified their correlation with mechanobiological responses through an in-silico approach. A 66-year-old male patient received mandibular reconstruction was studied. Post-operative CT scans were taken at 0, 4, 16 and 28 months. Longitudinal change of bone morphologies and mineral densities were measured at three bone union interfaces (two between the fibula and mandibular bones and one between the osteotomized fibulas) to investigate bone healing/remodeling events. Three-dimensional finite element models were created to quantify mechanobiological responses in the bone at these different time points. Bone mineral density increased rapidly along the bone interfaces over the first four months. Cortical bridging formed at the osteotomized interface earlier than the other two interfaces with larger shape discrepancy between fibula and mandibular bones. Bone morphology significantly affected mechanobiological responses in the osteotomized region (R
Publisher: Wiley
Date: 04-04-2012
DOI: 10.1111/J.1834-7819.2012.01681.X
Abstract: For a restorative material or adhesive to exhibit caries inhibitive potential through fluoride release, it must be capable of fluoride recharge. The aim of this study was to evaluate the effect of repeated fluoride recharge and different storage media on dentine bond strength durability. Two self-etch adhesive systems (two-step) were evaluated: fluoride-rechargeable Giomer FL-Bond II and non-fluoride-containing UniFil Bond. For each adhesive 32 human dentine specimens were prepared for shear bond strength testing. The specimens were randomly allocated to one of four storage groups: Group 1 - 24-hour water ageing Group 2 - four-month water ageing Group 3 - four-month water ageing with weekly fluoride recharge (5000 ppm for 10 minutes) and Group 4 - four-month acid ageing with weekly fluoride recharge. Weekly fluoride recharge over four months ageing did not significantly (p > 0.05) reduce the dentine shear bond strength of FL-Bond II or UniFil Bond. Storage media did not significantly (p > 0.05) affect bond durability. The adhesion between fluoride rechargeable FL-Bond II and dentine maintained durability despite regular fluoride recharge over the four months ageing. Clinicians prescribing the fluoride recharge regime used in the present study to reduce recurrent caries incidence associated with Giomer FL-Bond II restorations can do so without compromising dentine bond strengths.
Publisher: Wiley
Date: 05-12-2021
DOI: 10.5694/MJA2.51353
Publisher: SAE International
Date: 02-1983
DOI: 10.4271/830318
Publisher: Wiley
Date: 08-1991
Publisher: Elsevier BV
Date: 06-2015
DOI: 10.1016/J.DENTAL.2015.03.007
Abstract: To analyze the damage tolerance of indirect restorative materials after grinding with diamond burs to simulate adjustments by clinicians and technicians. Seven commercially available restorative materials (Mark II, ENAMIC, In-Ceram Alumina, VM 9, In-Ceram YZ, IPS e.max CAD) and an experimental one (PICN) were analyzed. Forty bending bars per material were fabricated according to manufacturer's instructions and lapped with 15 μm diamond suspension. The initial flexural strength was determined in three-point-bending on 10 specimens. Additionally the elastic modulus and Poisson's ratio were determined by the resonant frequency method. The remaining bending bars were ided into six groups (n=5) and subjected to standardized grinding with three different diamond grit burs (coarse, 151 μm medium, 107 μm and extra fine 25 μm) and two grinding directions (transversal and longitudinal). The ground specimens were subsequently loaded to fracture and analyzed by SEM. Except for the YTZP bending bars, the initial materials strength of all tested materials decreased significantly with all diamond burs upon adjustments in both transversal and longitudinal grinding directions. The resistance of the ground materials to strength reduction follow the order from highest to least damage tolerant material: PICN>ENAMIC>Mark II>VM 9>In-Ceram Alumina>IPS e.max CAD. The loss in strength of all examined materials after longitudinal grinding is generally less compared to transversal grinding. The lowest loss in strength occurred for VM 9 (7.79%) and ENAMIC (9.18%) upon longitudinal grinding direction with extra fine and medium diamond grit bur, respectively. The damage tolerance of restorative materials upon adjustments depends on specific mechanical properties and the adjustment procedure. The outcomes of the simulated grinding protocols of this study can be adopted clinically in terms of the selection of appropriate materials, burs and adjustment parameters.
Publisher: Trans Tech Publications, Ltd.
Date: 03-2010
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.97-101.2241
Abstract: Fabrication of multilayered ceramics signifies an important topic in many advanced applications aerospace and prosthetic dentistry. This paper presents a numerical approach to characterising the transient thermal responses and corresponding thermal residual stresses that are developed in the bi-layered dental ceramic crowns model under a controlled cooling rate from a temperature around its glass transition temperature (typically 550°C) to room temperature (25°C). Finite element method (FEM) is adopted to model the residual stresses in normal or rapid cooling fabrication process. The demonstrative ex les take into account the effect of thickness in core veneered all-ceramic restorative prosthesis (specific porcelain bonded to an alumina or zirconia core layer), cooling rates and mismatches in temperature-dependent material properties such as thermal expansion coefficients, specific heat and Young’s modulus. The model of transient ceramic fabrication processing showed significant potential to development of optimal prosthetic devices.
Publisher: Mary Ann Liebert Inc
Date: 03-2021
Publisher: Wiley
Date: 11-1992
Publisher: Wiley
Date: 07-1986
Publisher: Wiley
Date: 28-09-2010
DOI: 10.1002/JBM.A.32908
Abstract: Reconstituted keratin has shown promise as an orthopaedic biomaterial. This in vivo study investigates the biological response of composite materials prepared from reconstituted keratin containing a high content of hydroxyapatite (HA) (40 wt % HA), implanted for up to 18 weeks in the long bones of sheep. Keratin-HA composites were compared with a commercially available polylactic acid (PLA) HA composite (BIO RCI HA®, Smith and Nephew). Porous keratin-HA materials displayed excellent biocompatibility and osseointegration, with full integration into bone by 12 weeks. Dense keratin-HA materials also showed excellent biocompatibility, with a more limited osseointegration, involving the penetration of new bone into the periphery of the implant after eight weeks. In contrast, the PLA-HA implant did not integrate with surrounding tissue. Microindentation showed that porous keratin-HA implants were initially soft, but became stiffer as new bone penetrated the implant from four weeks onwards. In contrast, although the initial rigidity of dense keratin-HA composites was maintained for at least two weeks, the implant material weakened after four weeks. The PLA-HA implant maintained its physical properties throughout the course of the trial. This study demonstrates the increased osseointegration/osteoconduction capacity of keratin-HA composites and provides further evidence supporting the suitability of keratin-based materials, such as bone graft substitutes and soft tissue fixation devices.
Publisher: AIP Publishing
Date: 13-04-2201
DOI: 10.1063/1.1711164
Abstract: Indentation tests with loads between 0.5 and 10 mN were performed on fused quartz, (0001) oriented sapphire and (001) oriented barium titanate. The resulting submicron cracks were used to determine the fracture toughness KIC of the tested s les. The indentation crack length method was applicable, but a c/a dependency of the constant of proportionality was found. In addition, a very effective and simple approach—using the extra penetration of the indenter, due to the formation of cracks, so called pop-in—was used to determine KIC.
Start Date: 2008
End Date: 2010
Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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End Date: 2014
Funder: Australian Research Council
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End Date: 2005
Funder: National Health and Medical Research Council
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End Date: 2011
Funder: National Health and Medical Research Council
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Funder: Australian Research Council
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End Date: 2020
Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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Funder: Australian Research Council
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