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Untreated nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) lead to irreversible liver damage. We hypothesized that a low-fat diet (LFD) or a high-fat diet (HFD) with soy protein isolate (SPI) would be an effective intervention to halt or reverse NAFLD progression. To test these hypotheses, we conducted 2 studies. In the first study, we fed an HFD to 7-week-old C57BL/6J mice to induce NAFLD compared to an LFD (control). Hepatic steatosis was monitored by quantitative ultrasound (QUS) scans (in vivo and ex vivo). Animals were euthanized after 0, 2, 4, and 6 weeks of feeding. In the second study, 7-week-old mice were randomized onto an LFD or HFD with SPI intervention after 4 weeks of feeding HFD. Animals from each group were scanned with QUS and euthanized after 4, 9, and 12 weeks of feeding. Animals fed the HFD developed NAFLD (100%) and NASH (80%) characterized by increased liver weight, lipid accumulation, and histological scores for inflammation by 4 weeks in the first study. In the second study, the LFD ameliorated this NAFLD phenotype after 5 weeks of feeding; however, the SPI intervention failed to significantly attenuate NAFLD. QUS parameters were significantly increased with the HFDs (P < .05) and steatosis grade (P < .05) and were positively correlated with hepatic lipid concentrations. In conclusion, dietary modification may be effective at reversing NAFLD and NASH at early stages. Furthermore, QUS may become a valuable tool to track hepatic steatosis. Additional studies are needed to further evaluate the effectiveness of these interventions., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: Clinical failure of dental ceramics is usually reported as partial fracture of the restoration (chipping) or as catastrophic fracture of the whole structure. In contrast to metals, ceramics are linear-elastic, brittle materials exhibiting extremely low damage tolerance to failure. Well documented clinical and lab reports have shown this fracture event often occurs at loads far below their fracture strength due to intrinsic fatigue degradation via slow crack growth or cyclic fatigue mechanisms. The presence and development of surface flaws have a dominant role in damage accumulation and lifetime reduction of ceramic structures., Aims: This ADM guidance document aims to summarize the aspects related to fatigue degradation of dental ceramics, reviewing the concepts of fatigue testing and furthermore aims to provide practical guidance to young scientists entering into fatigue related research. The description of fatigue strength is always accompanied by a clear understanding of the underlying fracture mechanisms., (Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Background: There are limited comparative survival data for prostate cancer (PCa) patients managed with a low-dose rate brachytherapy (LDR-B) boost and dose-escalated external-beam radiotherapy (DE-EBRT) alone., Objective: To compare overall survival (OS) for men with unfavorable PCa between LDR-B and DE-EBRT groups., Design, Setting, and Participants: Using the National Cancer Data Base, we identified men with unfavorable PCa treated between 2004 and 2012 with androgen suppression (AS) and either EBRT followed by LDR-B or DE-EBRT (75.6-86.4Gy)., Outcome Measurements and Statistical Analysis: Treatment selection was evaluated using logistic regression and annual percentage proportions. OS was analyzed using the Kaplan-Meier method, log-rank test, Cox proportional hazards, and propensity score matching., Results and Limitation: We identified 25038 men between 2004 and 2012, during which LDR-B boost utilization decreased from 29% to 14%. LDR-B was associated with better OS on univariate (7-yr OS: 82% vs 73%; p<0.001) and multivariate analyses (hazard ratio [HR] 0.70, 95% confidence interval [CI] 0.64-0.77). Propensity score matching verified an OS benefit associated with LDR-B boost (HR 0.74, 95% CI 0.66-0.89). The OS benefit of LDR-B boost persisted when limited to men aged <60 yr with no comorbidities. On subset analysis, there was no interaction between treatment and age, risk group, or radiation dose. Limitations include the retrospective design, nonrandomized selection bias, and the absence of treatment toxicity, hormone duration, and cancer-specific outcomes., Conclusions: Between 2004 and 2012, LDR-B boost utilization declined and was associated with better OS compared to DE-EBRT alone. LDR-B boost is probably the ideal treatment option for men with unfavorable PCa, pending long-term results of randomized trials., Patient Summary: We compared radiotherapy utilization and survival for prostate cancer (PCa) patients using a national database. We found that low-dose rate brachytherapy (LDR-B) boost, a method being used less frequently, was associated with better overall survival when compared to dose-escalated external-beam radiotherapy alone for men with unfavorable PCa. Randomized trials are needed to confirm that LDR-B boost is the ideal treatment., (Copyright © 2017 European Association of Urology. Published by Elsevier B.V. All rights reserved.)

This guidance document describes the specific issues involved in dental multilayer ceramic systems. The material interactions with regard to specific thermal and mechanical properties are reviewed and the characteristics of dental tooth-shaped processing parameters (sintering, geometry, thickness ratio, etc.) are discussed. Several techniques for the measurement of bond quality and residual stresses are presented with a detailed discussion of advantages and disadvantages. In essence no single technique is able to describe adequately the all-ceramic interface. Invasive or semi-invasive methods have been shown to distort the information regarding the residual stress state while non-invasive methods are limited due to resolution, field of focus or working depth. This guidance document has endeavored to provide a scientific basis for future research aimed at characterizing the ceramic interface of dental restorations. Along with the methodological discussion it is seeking to provide an introduction and guidance to relatively inexperienced researchers., (Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: To provide background information and guidance as to how to use fractography accurately, a powerful tool for failure analysis of dental ceramic structures., Methods: An extended palette of qualitative and quantitative fractography is provided, both for in vivo and in vitro fracture surface analyses. As visual support, this guidance document will provide micrographs of typical critical ceramic processing flaws, differentiating between pre- versus post sintering cracks, grinding damage related failures and occlusal contact wear origins and of failures due to surface degradation., Results: The documentation emphasizes good labeling of crack features, precise indication of the direction of crack propagation (dcp), identification of the fracture origin, the use of fractographic photomontage of critical flaws or flaw labeling on strength data graphics. A compilation of recommendations for specific applications of fractography in Dentistry is also provided., Significance: This guidance document will contribute to a more accurate use of fractography and help researchers to better identify, describe and understand the causes of failure, for both clinical and laboratory-scale situations. If adequately performed at a large scale, fractography will assist in optimizing the methods of processing and designing of restorative materials and components. Clinical failures may be better understood and consequently reduced by sending out the correct message regarding the fracture origin in clinical trials., (Copyright © 2017 The Academy of Dental Materials. All rights reserved.)

Objectives: to evaluate the influence of the occlusal resin cement thickness on the cyclic loads-to-failure of feldspathic crowns and to compare the results to data from monotonic tests. A large range of cement thickness (50μm and 500μm) was tested, in order to better measure the influence of this variable., Methods: Feldspathic ceramic crowns (Vita Mark II blocks, Vita Zahnfabrik) were bonded to dentin analog dies (G10 (NEMA grade G10, International Paper), with occlusal resin cement thicknesses of 50μm and 500μm (Multilink Automix, Ivoclar). The dies were prepared with microchannels for water transport to the cement layer. After 96-h water storage, the specimens (n=20) were submitted to cyclic loads (500,000 cycles at 20Hz; initial maximum load=40% of monotonic load, from previous data) following a staircase sensitivity design (step size=25N). Failure loads at 500,000 cycles were compared to monotonic failure loads (from a previous study with specimens produced by the same author, using the same materials, specimen configuration and cementation protocol)., Results: Crowns with an occlusal cement layer of 50μm were more resistant than those cemented with 500μm (246.4±22.9N vs. 158.9±22.9N), under wet cyclic testing conditions (p<0.001). The fatigue failure loads were reduced compared to monotonic loads: to 37% of monotonic for 50μm; to 53% of monotonic for 500μm., Significance: An occlusal cement thickness of 50μm was more favorable for the structural performance of feldspathic crowns than was 500μm. Cyclic fatigue reduced failure loads well below those found under monotonic loading., (Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Purpose: This study evaluated failure behavior when resin-composite cylinders bonded to dentin fractured under traditional "shear" testing. Failure was assessed by scaling of failure loads to changes in cylinder radii and fracture surface analysis. Three stress models were examined including failure by: bonded area; flat-on-cylinder contact; and, uniformly-loaded, cantilevered-beam., Methods: Nine 2-mm dentin occlusal dentin discs for each radii tested were embedded in resin and bonded to resin-composite cylinders; radii (mm)=0.79375; 1.5875; 2.38125; 3.175. Samples were "shear" tested at 1.0mm/min. Following testing, disks were finished with silicone carbide paper (240-600grit) to remove residual composite debris and tested again using different radii. Failure stresses were calculated for: "shear"; flat-on-cylinder contact; and, bending of a uniformly-loaded cantilevered beam. Stress equations and constants were evaluated for each model. Fracture-surface analysis was performed., Results: Failure stresses calculated as flat-on-cylinder contact scaled best with its radii relationship. Stress equation constants were constant for failure from the outside surface of the loaded cylinders and not with the bonded surface area or cantilevered beam. Contact failure stresses were constant over all specimen sizes. Fractography reinforced that failures originated from loaded cylinder surface and were unrelated to the bonded surface area., Conclusions: "Shear bond" testing does not appear to test the bonded interface. Load/area "stress" calculations have no physical meaning. While failure is related to contact stresses, the mechanism(s) likely involve non-linear damage accumulation, which may only indirectly be influenced by the interface., (Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: To assess transient and residual stresses within the porcelain of veneered restorations (zirconia and metal) as a result of cooling rate and porcelain thickness., Methods: Porcelain-on-zirconia (PZ) and porcelain-fused-to-metal (PFM) crowns were fabricated with 1 or 2mm of porcelain. Thermocouples were attached both internally and externally to the crowns to record transient temperatures. For fast cooling, the furnace was opened after the holding time and switched off. Slow cooling was accomplished by opening the furnace at 50°C below the glass transition temperature (Tg) of the material. An axially symmetric FEA model simulated thermal stresses. Time-dependent temperature equations from thermocouple readings were set as boundary conditions. Framework materials and the porcelain below Tg were considered to behave elastically. Visco-elastic behavior was assumed for porcelain above the Tg modeling properties as dependent on cooling rate., Results: Differences in residual stress were found for fast and slow cooled PZ and PFM crowns. Significant transient stress waves were observed within the porcelain when fast cooling through Tg. They are believed to be related to non-uniform volumetric changes originated from thermal gradients. Results were confirmed by modeling and physical testing of crowns containing a defect., Significance: Residual stresses do not distinguish PZ from PFM. High magnitude transient stresses observed within the porcelain during fast cooling may explain clinical fractures involving internal defects. Stress waves may also originate internal micro-cracking which could grow under function. Therefore, slow cooling, especially for all-ceramic crowns with thick porcelain, is important to prevent thermal gradients and high-magnitude transient stresses., (Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objective: The present work evaluated the thermal behavior of porcelain-metal and porcelain-zirconia restorations during fast and slow firing and cooling., Methods: All-ceramic (porcelain on zirconia) and porcelain-fused-to-metal (PFM) molar crowns were fabricated with 1 or 2mm porcelain thickness. Thermocouples were attached to the cementation (T1) and occlusal (T4) surfaces of the restoration and embedded at the framework-porcelain interface (T2) and inside the porcelain (T3) to acquire temperature readings by time. Slow heating was set as 45°C/min and fast heating as 140°C/min. For fast cooling, the furnace was opened immediately after the holding time. Slow cooling was effected by opening the furnace when it reached 50°C below the Tg. Porcelains Tg were calculated for each cooling rate., Results: Slow heating rate was measured at T4 as being 30°C/min while fast heating at T4 was 100°C/min. The measured cooling rates within the porcelain (T2) around the Tg range were 20°C/min and 900°C/min for slow and fast cooling, respectively. During slow cooling, similar temperatures were found for both zirconia and metal crowns. Remarkable temperature gradients were observed for the fast cooled all-ceramic crown (T1-T4=100°C) and, of lower magnitude for PFM (T1-T4=30°C). Tg of porcelains increase with faster cooling rates., Significance: Slow cooling appears to be especially important for all-ceramic crowns to prevent high magnitude thermal gradients, which could influence cracking and fracture of the porcelain., (Copyright © 2013 Academy of Dental Materials. All rights reserved.)

Objectives: Clinical experience with implant-supported dentures indicates that fracture and chipping of teeth are becoming an issue. Tooth fracture and chipping rates of approximately 2.5% per year are being experienced at one university. There has been no standardized test developed for bulk fracture or chipping of denture teeth. Such a test would aid in the development of improved teeth and in their evaluation., Methods: Central incisor teeth were embedded in acrylic and loaded on incisal edges at 90° to their long axes. Teeth tested included ones commercially available and two sets made from improved materials designed to increase toughness. Cyclic loading was done at 5Hz from 20N to 135N, 150N, 175N and 200N. Data was analyzed using lifetime analysis software fit at each of the accelerated loads and then extrapolated to clinical use loads (Alta 7, Reliasoft Corp.) Clinical use loads were derived from extrapolation of probability of failure (Pf) data to 2.5% Pf., Results: When carefully embedded, teeth could be reproducibly loaded to failure by bulk fracture involving a failure mode similar to that seen clinically. Clinical use loads were calculated to be in the range of 70N. Results from accelerated loading could be fit to similar probability of failure distributions allowing extrapolation to clinical use loads., Significance: This work was able to develop a clinically valid bulk fracture test for the fatigue failure of incisor denture teeth. It appears that teeth fabricated with improved materials will be expected to perform better clinically. Thus both the null hypotheses were rejected., (Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objective: The aim of this study was to analyze the influence of polymerization shrinkage of the cement layer on stresses within feldspathic ceramic crowns, using experimentally validated FEA models for (1) increasing occlusal cement thickness; and, (2) bonded versus non-bonded ceramic-cement interfaces., Methods: 2-D axial symmetric models simulated stylized feldspathic crowns (1.5mm occlusal thickness) cemented with resin-cement layers of 50-500μm on dentin preparations, being loaded (500N) or not. Ceramic-cement interface was either bonded or not. Cement was bonded to the dentin in all models. Maximum axial shrinkage of 0%, 1%, 2%, 3%, 4% and 4.65% were simulated. The first principal stresses developing in the cementation surface at the center and at the occluso-axial line-angle of the crown were registered., Results: Polymerization shrinkage of the cement increased tensile stresses in the ceramic, especially in loaded non-bonded crowns for thicker cement layers. Stresses in loaded non-bonded crowns increased as much as 87% when cement shrinkage increased from 0% to 4.65% (100-187MPa), for a 500μm-thick cement. Increasing polymerization shrinkage strain raised the tensile stresses, especially at the internal occlusal-axial line-angle, for bonded crowns., Significance: Changes in the polymerization shrinkage strain (from 0% to 4.65%) have little effect on the tensile stresses generated at the cementation surface of the ceramic crowns, when the occlusal cement thickness is thin (approx. 50μm for bonded crowns). However, as the cement becomes thicker stresses within the ceramic become significant., (Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Purpose: The objective was to compare absolute translucency with a frequently used surrogate measure of relative translucency (contrast ratio) from 14 all-ceramic materials having a wide range of translucencies., Materials and Methods: Standardized disks were fabricated from fourteen ceramics, varying both thickness (0. 3mm, 0.5 mm, 1.0 mm, and 1.5 mm) and chroma (high and low). Absolute translucency (percent transmission) was measured using a spectroradiometer with an integrating sphere. Relative translucency was measured using a spectrophotometer as contrast ratio (contrast ratio; ratio of L* values recorded on black and white backgrounds). Non-linear regression was used to compare measurements of absolute versus relative values for each of the spectrophotometers., Results: Contrast ratio was not able to characterize translucency across the range of materials studied and became less sensitive with increasing opacity. A non-linear correlation was found between percent transmission and contrast ratio down to 50% transmission (r(2)=0.97) and contrast ratio was insensitive to transmission differences below 50% transmission., Conclusion: Contrast ratio is not a direct measure of translucency and cannot be used below 50% transmission., (Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: Bonding of all-ceramic restorations has become routine practice mainly due to results from clinical studies. Sandblasting has been advocated for surface treatment of many ceramics, based on results from numerous in vitro studies. This present work examines the influence of bonding on fracture loads of a veneered alumina ceramic using both chemical and sandblasting treatments., Methods: Veneered tabs (In-Ceram alumina) were cemented (50 μm; ZnPO(4) or Panavia 21) to dentin-analog bases designed to allow water penetration to the cement/dentin interface. 60 specimens were fabricated for 2 weeks storage and another 80 specimens for 6 months storage (water, 37°C). Half of each group was tested "as-finished" and the other half "as-sandblasted", each divided between two cements. Specimens were loaded cyclically (20 Hz, 500,000) cycles in water beneath a 3mm diameter piston. A staircase sensitivity protocol was followed, using a step size of 25 N. Specimens were examined for cracking by transillumination (10×)., Results: Mean failure loads differed significantly between (1) as-finished Panavia versus zinc phosphate at 2 weeks; (2) as-finished versus sandblasted at 2 weeks; and (3) as-finished at 6 months versus 2 weeks (ANOVA, 95% post hoc test). Sandblasted groups did not differ among themselves at either time period or between 2 weeks and 6 months., Conclusion: Sandblasting was important for maintaining failure loads after 6 months of water storage. Zinc phosphate was equally protective as Panavia for sandblasted groups. Adhesion testing may not replicate clinical stresses important for investigating protective cement effects., (Copyright © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objective: To determine the influence of cement thickness and ceramic/cement bonding on stresses and failure of CAD/CAM crowns, using both multi-physics finite element analysis and monotonic testing., Methods: Axially symmetric FEA models were created for stress analysis of a stylized monolithic crown having resin cement thicknesses from 50 to 500 μm under occlusal loading. Ceramic-cement interface was modeled as bonded or not-bonded (cement-dentin as bonded). Cement polymerization shrinkage was simulated as a thermal contraction. Loads necessary to reach stresses for radial cracking from the intaglio surface were calculated by FEA. Experimentally, feldspathic CAD/CAM crowns based on the FEA model were machined having different occlusal cementation spaces, etched and cemented to dentin analogs. Non-bonding of etched ceramic was achieved using a thin layer of poly(dimethylsiloxane). Crowns were loaded to failure at 5 N/s, with radial cracks detected acoustically., Results: Failure loads depended on the bonding condition and the cement thickness for both FEA and physical testing. Average fracture loads for bonded crowns were: 673.5 N at 50 μm cement and 300.6N at 500 μm. FEA stresses due to polymerization shrinkage increased with the cement thickness overwhelming the protective effect of bonding, as was also seen experimentally. At 50 μm cement thickness, bonded crowns withstood at least twice the load before failure than non-bonded crowns., Significance: Occlusal "fit" can have structural implications for CAD/CAM crowns; pre-cementation spaces around 50-100 μm being recommended from this study. Bonding benefits were lost at thickness approaching 450-500 μm due to polymerization shrinkage stresses., (Copyright © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: This paper attempts to provide critical perspectives on common in vitro research methodologies, including shear bond testing, wear testing, and load-to-failure tests. Origins of interest in high-quality laboratory data is reviewed, in vitro data is categorized into property and simulation protocols, and two approaches are suggested for establishing clinical validity. It is hoped that these insights will encourage further progress toward development of in vitro tests that are validated against clinical performance and/or by producing clinically validated failure or damage mechanisms., Materials and Methods: Published shear and tensile bond data (macro and micro) is examined in light of published finite element analyses (FEA). This data is subjected to a Weibull scaling analysis to ascertain whether scaling is consistent with failure from the bonded interface or not. Wear tests results are presented in light of the damage mechanism(s) operating. Quantitative wear data is re-examined as being dependent upon contact pressure. Load-to-failure test results are re-analyzed by calculating contact stresses at failure for 119 tests from 54 publications over more than 25 years., Results: FEA analyses and reported failure modes (adhesive, mixed, cohesive) are consistent with failure not involving interfacial "shear stresses" as calculated in published work. Weibull scaling clearly suggests failure involving external surfaces of specimens, not interfacial origins. Contact stresses (pressures) are clearly an important variable in wear testing and are not well-controlled in published work. Load-to-failure tests create damage not seen clinically due to excessively high contact stresses. Most contact stresses in the 119 tests examined were calculated to be between 1000MPa and 5000MPa, whereas clinical contact stresses at wear facets have been measured not to exceed 40MPa., Conclusions: Our community can do a much better job of designing in vitro tests that more closely simulate clinical conditions, especially when contact is involved. Journals are encouraged to thoughtfully consider a ban on publishing papers using bond tests and load-to-failure methods that are seriously flawed and have no clinical relevance., (Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: Surface conditions are of interest in all-ceramic restorations since they can control both bonding and strength. Tensile testing methods are commonly used to evaluate surface conditions of ceramics. This work evaluated tensile properties of a feldspathic ceramic as-finished, sandblasted and etched under three stressing conditions: (1) biaxial flexure; (2) monotonic mastication loading, dry; and, (3) cyclic mastication loading, wet., Materials and Methods: Feldspathic CAD/CAM blocks were sliced into Tabs 1mm thick, n=135 specimens were divided into 3 groups assigned to as-finished (600 grit SiC; control), sandblasted, and etched. Of the 45 specimens per group, 35 specimens were used for bonded tests and 10 specimens for biaxial flexure testing. Pin-on-three ball biaxial testing was performed per ISO 6872. 35 specimens were bonded to dentin-analog bases and loaded to radial crack pop-in beneath a 3mm diameter piston. 20 specimens were tested dry with failure determined by acoustic emission methods. 15 specimens, bonded to bases having micro-channels for water transport, were cyclically loaded beneath the 3mm piston under water at 15Hz for 500,000 cycles., Results: Biaxial flexure distinguished among all three surface conditions (p<0.05, ANOVA). Monotonic testing could not distinguish among groups. Cyclic testing could not distinguish between sandblasted and etched groups but both were weaker than as-finished., Conclusions: Mastication loading of bonded specimens creates a different stress state than simple flexure due to contributions of the cement-ceramic interface. Water adds a damage accumulation effect. Tensile stress conditions need to be chosen with the desired outcomes considered., (Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objectives: To test the hypotheses that shear bond strength (sigma(s)) and contact angle (theta) are influenced by the thermal expansion/contraction behavior of bilayered all-ceramic systems., Methods: Glass-infiltrated ceramics (A - In-Ceram ALUMINA) and zirconia-reinforced alumina (Z - In- Ceram ZIRCONIA) were veneered with feldspathic ceramics (7 - VM7; 9 - VM9; 13 - VM13), yielding 6 experimental groups. Surface roughness (Ra) of A and Z core ceramic disks (12 mm diameter x 1.2 mm high) was measured to assure that values were similar. A cylinder of veneer (2 mm diameter x 2 mm high) was fired onto the center of all core disks, cooled under identical conditions and tested for sigma(s) to failure (n=20). For the theta evaluation (n=10) similar specimens (veneer 1 mm high) were overfired to develop an equilibrium theta that was then measured from digital images (AutoCAD 2006). Published thermal expansion data were used., Results: The mean values of sigma(s) (MPa) and theta (degrees) for the core-veneer ceramic groups were, respectively: A7 (19.4+/-4.7; 49+/-4.7); Z7 (23.4+/-6.2; 56+/-4.9); A9 (0.9+/-1.6; 55+/-5.8); Z9 (9.8+/-5.7; 59.8+/-2.9); A13 (0; 70+/-6.0); Z13 (0; 67.2+/-6.3). As the difference in coefficient of thermal expansion (coreveneer) increases, the theta value increases (r=0.95) and the sigma(s) value decreases (r=-0.92), p

Objectives: Preliminary studies on implant fatigue testing suggested that fractures were more likely to occur at 2 Hz than at 30 Hz (chi(2), p<0.05). This investigation explores frequency and base elastic modulus effects on strain, strain rate and failure., Methods: A total of 66 implants were mounted in different base materials (acrylic, glass-filled epoxy, aluminum) and loaded up to 10(6) cycles per ISO 14801 (20 N to 420-500 N) at frequencies of 2 Hz and 30 Hz (chosen to accelerate frequency as the stressor). Absolute strain magnitudes and strain rates under varying loading conditions and with different base materials were measured using one strain-gauged implant. Failure probability distributions were analyzed by both Weibull and life data analysis. Measured strain was used to validate an FEA model. Fracture surfaces were examined by SEM., Results: Number of failures and failure-rates-per-cycle differed significantly between implants tested at 2 Hz versus 30 Hz (p<0.05). Strain magnitude was independent of frequency. Strain rates were highly correlated with frequency (linear r(2)>0.99) and differed significantly under failure conditions (420 N): 2 Hz=8292 microstrain/s; (500 N): 30 Hz=80,840 microstrain/s. Measured and FEA-calculated strains were similar. Fracture surfaces were indistinguishable (2 Hz versus 30 Hz)., Significance: Fatigue failure was significantly more likely at 2 Hz than 30 Hz whereas base material and loading magnitude seemed to have only minor influence. Absolute strain was identical at these frequencies suggesting strain rate sensitivity for this commercially pure titanium implant. Both the Weibull and SEM analyses support an identical failure mechanism with damage accumulation more severe at lower frequencies, an interpretation consistent with strain rate sensitivity.

Objectives: This work begins to explore the influence of cycling rate and environment on fatigue testing of dental implants according to the ISO protocol 14801., Methods: Twenty-four Straumann implants (4.1 mm x 12 mm) were tested up to five million cycles per ISO 14801: loaded at either 2 or 30 Hz in room air at 25 degrees C or normal saline at 37 degrees C (n=6 per group). Implant displacements/cycle were captured during all testing. Fracture-surface features were examined using scanning electron microscopy (n=12). Two complimentary methods were developed to estimate fatigue crack growth rates., Results: Failures (bulk fracture) were found to be bi-modally distributed, either <350,000 cycles or >1.5 million cycles at both cycling rates. Following initial crack formation, fatigue crack growth required merely 1100-4200 cycles to failure. Initial crack pop-in was statistically more likely under 2 Hz than 30 Hz (chi(2), p<0.05) but testing in air and normal saline were equivalent in terms of likelihood of fracture versus runout (chi(2), p>0.6). On a microscopic level, fatigue crack growth rates appears to be similar at 2 and 30 Hz, but may be slower in the presence of saline versus dry at 2 Hz., Significance: Implant failure under fatigue conditions involved "classic" damage mechanisms. Failure appears more likely at 2 Hz than 30 Hz for reasons that remain to be elucidated. Saline may enable chemically assisted crack growth involving grain boundaries during the stage of fatigue crack growth, but did not influence likelihood of failure.

Objectives: The purpose of this study was to derive a simple closed-form solution for the stress distribution through the thickness of multilayered discs subjected to biaxial moment loading, such that it can be used readily to evaluate the biaxial strength of multilayered dental ceramics using biaxial flexure tests., Methods: A simple analytical model was developed to derive the stress distribution through the thickness of multilayered discs subjected to biaxial moment loading. The accuracy of the solution was verified by comparing with previous rigorous analytical solutions and finite element results. The results obtained from Roark's formulas for bilayered discs were also included for comparison., Results: Examples of porcelain/zirconia bilayered discs subjected to ring-on-ring and piston-on-ring loadings were used for comparison among different analyses. Despite the simplicity in deriving the present solution, it is sufficiently accurate in comparing with previous rigorous solutions and finite element results. Also, if the biaxial stresses on the top and the bottom surfaces of the disc can be measured during testing, the biaxial stress/strain through the entire thickness of the multilayered disc can be determined using equations derived in the present model., Significance: International Organization for Standardization has selected piston-on-three-ball tests to establish ISO 6872 for dentistry-ceramic materials. However, monolayered specimens are considered in tests for this standard. While dental materials are usually fabricated into layered structures, modification of the current standard is essential. Our simple closed-form solution serves as a basis for extending the current standard to multilayered systems.

This review introduces concepts and background from the ceramics engineering literature regarding metastable zirconia ceramics to establish a context for understanding current and emerging zirconia-based dental ceramics.

Zirconia has been recently introduced in prosthetic dentistry for the fabrication of crowns and fixed partial dentures, in combination with CAD/CAM techniques. This review encompasses the specific types of zirconia available in dentistry, together with their properties. The two main processing techniques, soft and hard machining, are assessed in the light of their possible clinical implications and consequences on the long-term performance of zirconia. An update on the status of clinical trials occurring worldwide is provided.

Objective: This study investigated whether contact area (i.e. facet size) would influence the loads necessary for subsurface radial crack formation in porcelain specimens bonded to a dentin analog material., Methods: Dental porcelain discs (0.5 mm, 1 mm, and 1.5 mm thick) were bonded to compliant bases simulating dentin, and loaded with either a 1 mm, 2 mm, or 3 mm diameter aluminum piston until fracture. Pop-in of the subsurface radial crack from the bonded interface was detected using the acoustic emission (AE) method. Pre-test and post-test finite element analysis (FEA) was used to model the experiment and to calculate subsurface failure stresses., Results: There were significant differences in loads sustained before fracture according to both the ceramic thickness and the piston diameter (p<0.05; ANOVA and post-hoc Scheffe). Failure loads were found to be proportional to the square of the porcelain thickness. For all thicknesses, significantly higher loads were sustained beneath the 3mm piston than beneath the 1mm piston. FEA calculated failure strengths for the 1 mm thick porcelain (calculated from experimental mean loads) differed significantly for loading with the 1mm piston (168 MPa) or 3 mm piston (60 MPa)., Conclusions: It appears that both ceramic thickness and contact facet size may be clinically controlled to increase load-bearing ability of all-ceramic crowns. Single value strengths may not accurately model bonded dental ceramics; adjustments such as with Weibull scaling may improve accuracy. These results further suggest that small spherical indenters do not create clinically analogous contact conditions.

Objectives: Develop fractographic techniques to perform failure analyses of three ceramic whole-crown clinical failures., Methods: Three clinical whole-crown failures of different ceramic material systems were studied. The systems included appropriate veneers applied to core materials of cold isostatically pressed alumina, injection molded alumina/alumina-magnesia spinel, and hot pressed lithium disilicate. The surface topography was examined for classical fractographic features, utilizing both optical and scanning electron microscopes independently as well as group examination by four fractographers., Results: All three restorations displayed many common fractographic features, the most important of which was wake hackle. Wake hackle occurs when an approaching crack front sweeps by a small bubble or discontinuity in a brittle material, leaving a trail. The resulting trails can be used to trace back crack progression to an initial starting area. Wake hackle was found to be common in the veneer portions of the crowns, and the strategy of creating a wake hackle map enabled crack paths to be traced from a core area outward in all three restorations. The fracture origin areas were located where hoop stresses are high. Another helpful fracture feature was compression curl, an indication of flexural stress, most visible under low incident optical lighting., Significance: This study indicates that fractographic analyses can be productively performed on ceramic whole-crown failures. Optical examination under low incident lighting and wake hackle mapping were developed as promising techniques. Hoop stress was implicated as a concern in the three studied specimens, and should be considered when analyzing other whole-crown failures.

Objective: To assess the accuracy of potassium measurements in clinical laboratories across Canada., Design and Method: The flame atomic emission spectrophotometry reference method for the determination of potassium was established at the Canadian Reference Laboratory by using National Institute of Science and Technology standard reference materials. The method was subsequently used to assign target values for potassium to Canadian Reference Laboratory's External Quality Assessment human-serum-based testing material. A total of 503 laboratories participated and 9,279 individual External Quality Assessment test results were included in the study. Bias was determined by using difference plots., Results: Clinically significant bias (>1.6%) was observed in 45.9% of the laboratories. Bias ranged from 0.34 mmol/L to -0.54 mmol/L. At low concentrations (<3.5 mmol/L) a positive bias was most frequently observed (14.7% of analytical systems). At high potassium concentrations (>5.1 mmol/L) a negative bias was most frequently observed (31.4% of analytical systems)., Conclusion: Inaccuracy in potassium results can contribute to test redundancy and mismanagement of patients, while prohibiting the merger of laboratory data from disparate testing sites for the purpose of trending and consolidation within a "universal health record." Inaccurate test results and the lack of standardization among laboratories adversely impact our ability to establish common reference intervals and critical limits. This inability has an adverse effect on medical decisions and patient care.

Objectives: Fractographic analysis of indentation cracks is performed following flexure testing as part of the ASTM (1999) standard for fracture toughness, KIc, determination in advanced ceramics. This method depends on the conduciveness of the material towards fractographic interpretation. The purpose of this study was to evaluate the use of fractography in fracture toughness methods with a feldspathic dental porcelain, in which KIc was measured fractographically as well as numerically using two controlled-flaw beam bending techniques., Methods: The following methods for KIc determination were applied to a dental porcelain containing a leucite volume fraction of 15-20%: (1) surface crack in flexure (SCF) (dependent upon fractographic analysis); and (2) indentation strength (IS) at indentation loads of 9.8 and 19.6 N (applying both standard numeric calculations and fractographic analysis). The testing environments were (1) ambient air (IS and SCF) and (2) flowing dry nitrogen (SCF)., Results: No significant differences were found between numeric and fractographic KIc values for the IS technique at both indentation loads (9.8 and 19.6 N) in ambient air, although KIc values were sensitive to indentation load. Due to the presence of residual stresses, stable crack extension was observed fractographically in all IS specimens, as evidenced by differences between initial (ainitial) and critical (acritical) crack dimensions. For the SCF method, there was a significant difference in toughness between specimens tested in air versus dry nitrogen, however no fractographic evidence for chemically assisted slow crack growth (SCG) was observed., Significance: The SCF method as described by the ASTM standard was applicable to the feldspathic porcelain and produced very comparable results with the numeric toughness calculations of the IS procedure. However, fractographic analysis of the surface crack was somewhat difficult for this glassy ceramic compared with polycrystalline ceramics. Knowledge about stable crack extension or slow crack growth and its fractographic appearance is essential when estimating the toughness from examination of flaw dimensions on fractured surfaces since large calculation errors may occur if these effects are not taken into account.

Strength values are often relied upon as indicators of structural performance for brittle dental materials. Strength, however, is more of a "conditional" than an inherent material property, and strength data alone cannot be directly extrapolated to predict structural performance. Strength data are meaningful when placed into context via knowledge of material microstructure, processing history, testing methodology, testing environment and failure mechanism(s). Structure failure is determined by additional failure probability variables (in concert with strength) that describe stress distributions, flaw size distributions, and that can account for either single or multiple failure modes. Lifetime predictions require additional information about the time dependence of slow crack growth. Basic fracture mechanics principles and Weibull failure modeling will be reviewed for the perspective they provide in understanding strength and the data obtained using various laboratory tests. Examples will be given to demonstrate how failed specimens can provide crucial information to either validate or question the failure mechanisms invoked during laboratory testing. The role of interfacial stresses is discussed as applied to dental structures of current interest. Overall, it is emphasized that an understanding of actual clinical failure modes is absolutely necessary before results of in vitro strength testing can be considered to have clinical validity.