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Abstract This study aimed to characterize the fatigue behavior using two fatigue methods, boundary and staircase, and to predict the probability of failure (P f) of zirconia-reinforced lithium silicate glass-ceramic (ZLS). Bar-shaped specimens of ZLS (18 ×4 ×1.2 mm) were fabricated. Thirty specimens were subjected to a three-point flexural strength test using a universal testing machine with 0.5 mm/min crosshead speed, in 37 °C distilled water. Flexural strength data were analyzed with Weibull statistics. Eighty-six bars were subjected to cyclic fatigue using boundary and staircase methods. Fatigue tests were performed in a pneumatic cycling machine (2 Hz, 37 °C distilled water) for 10 ³ and 104 cycles. Fatigue data were analyzed using an inverse power law relationship and log normal-lifetime distribution. Fracture toughness (K Ic) was determined using V-notched specimens (18 ×4 ×3 mm) and the short beam toughness method (n = 7). Vickers hardness (VH) was evaluated (4.9 N, 20 s). Fractographic and EDS analyses were also performed. ZLS showed a characteristic strength of 197 MPa, Weibull modulus of 4, VH of 6.67 GPa and K Ic of 1.93 MPa m1/2. After 103 cycles, for both methods, there was a degradation of 78% of the initial strength. There was no significant degradation when the number of cycles increased from 103 to 104. Both methods resulted in similar P f and precision at 40 MPa (~50% P f). Yet, staircase shows good accuracy and precision in predicting the stress amplitude for a P f near 50%; while boundary is also effective for P f lower than 50%. The fatigue methods evaluated show similar accuracy and precision for predicting the P f of a glass-ceramic when simulations were made in the range of stress levels and lifetimes used in the fatigue tests. Highlights • Both methods showed similar accuracy and precision for predicting 50% P f of ceramics. • Boundary method is efficient to predict low values of P f. • ZLS glass-ceramic has a significant strength degradation under fatigue. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the survival of maxillary anterior cantilever resin-bonded metal-ceramic (MC) and all-ceramic (AC) fixed dental prostheses (RBFDPs). Materials and Methods: Between August 2007 and December 2009, 40 patients received 40 RBFDPs made of either cobalt-chromium-ceramic (n = 20) or glass-infiltrated alumina (In-Ceram, Vident; n = 20) and were followed up until December 2012. Restorations were adhesively cemented (Panavia 21, Kuraray). Results: Two fractures were observed with AC. No debondings were observed with MC (n = 0) but were observed with AC (n = 3). The difference in survival rates of MC and AC was not significant (MC: 100%; AC: 90%; P = .15) (Kaplan-Meier method, confidence interval = 95%). Conclusions: Cantilever AC RBFDPs could be a promising alternative to MC RBFDPs for replacement of missing anterior incisors, provided that no mechanical complications were experienced with the latter. [ABSTRACT FROM AUTHOR]

Ultra-translucent zirconias are drawing immense attention due to their fascinating esthetic appearance. However, the high translucency came at the expense of diminishing strength along with the reduced ability of transformation toughening due to the increased cubic zirconia content. We aim to address these issues by infiltrating glass on the surface of an ultra-translucent zirconia (5Y-PSZ). Glasses of different shades can be used and the resulting graded glass/zirconia layer is expected to improve the material's flexural strength without compromising its esthetics. We also aim to elucidate how clinically relevant surface treatments-namely, air abrasion, glazing, or polishing-affect the fracture resistance of these zirconias with a high cubic content. All surface treatments were performed on bar-shaped (2 × 3 × 25 mm3) and plate-shaped (12 × 12 × 1 mm3) specimens, which were then subjected to a 4-point bending test and translucency measurements, respectively. 5Y-PSZ proved to be significantly more translucent than 3Y-TZP but also much weaker. Our hypothesis was accepted, as the strength of the glass-infiltrated ultra-translucent 5Y-PSZ (582 ± 20 MPa) is over 70% higher than its uninfiltrated counterpart (324 ± 57 MPa). Its strength is also over 25% higher than the highly polished 5Y-PSZ (467 ± 38 MPa). In addition, the translucency of 5Y-PSZ (translucency parameter [ TP] = 34, contrast ratio [ CR] = 0.31) is not affected by glass infiltration ( TP = 34, CR = 0.32) when the residual surface glass is removed by gentle polishing using 6- and then 3-µm diamond grits. Finally, both air abrasion and the presence of a glaze layer on the tensile surface decreased flexural strength significantly, being 274 ± 55 and 211 ± 21 MPa, respectively. With a combined high strength and translucency, the newly developed glass-infiltrated 5Y-PSZ may be considered a suitable material for next-generation, damage-resistant, and esthetic dental restorations. [ABSTRACT FROM AUTHOR]

Four pressure-sensitive phenomenological constitutive models for brittle ceramics are compared to available experimental data over a wide range of materials and confinement pressures. It is shown that the linear Mohr–Coulomb and Drucker Prager models are only applicable at low pressures. While the nonlinear strain-rate dependent Johnson–Holmquist (JH-2) model provides a reasonable fit to experimental data up to HEL for most materials, it completely fails to capture the experimentally observed pressure and strain-rate independent strength saturation of ceramics at pressures beyond HEL. It is demonstrated that the extended Mohr–Coulomb model is the only model that can not only capture the linear response at low pressures, but also the experimentally observed nonlinear response at higher pressures up to HEL and the pressure-independent response beyond HEL with a single curve. Further, the constants used in this model are shown to be universal and applicable to most brittle materials, allowing the model to be used in the absence of additional experimental data. The potential to extend the extended Mohr–Coulomb model to damaged ceramics and its implementation into computational codes is also discussed. [ABSTRACT FROM AUTHOR]

The effects of moderate intensity ‘hot’ or ‘cold’ shock in brittle solids have been extensively studied, while much less is known about thermal shock response during large temperature variations. In this study, a combined finite element – peridynamics numerical procedure is proposed for the simulation of cracking in ceramic materials, undergoing severe thermal shock. Initially, Finite Element nonlinear heat transfer analysis is conducted. The effects of surface convection and radiation heat exchange are also included. Subsequently, the interpolated temperature field is used to formulate a varying temperature induced action for a bond-based peridynamics model. The present model, which is weakly coupled, is found to reproduce accurately previous numerical and experimental results regarding the case of a ‘cold’ shock. Through several numerical experiments it is established that ‘cold’ and ‘hot’ shock conditions give rise to different failure modes and that large temperature variations lead to intensified damage evolution. [ABSTRACT FROM AUTHOR]

In recent years, numerous studies have been conducted on the crack-healing behavior of ceramic materials. Design of ceramic structures with the ability of crack-healing in service is one of the most important objectives of many scientists. Development of such structures in fuel cells, aerospace, automotive and military industries can save a lot of money from a maintenance cost viewpoint. This paper addresses the most recent findings from researchers in the field of crack-healing in ceramics and discusses future perspectives in this research area. [ABSTRACT FROM AUTHOR]

The effects of control mode and test rate on the measured fracture toughness of ceramics were evaluated by using chevron-notched flexure specimens in accordance with ASTM C1421. The use of stroke control gave consistent results with about 2% (statistically insignificant) variation in measured fracture toughness for a very wide range of rates (0.005 to 0.5 mm/min). Use of strain or crack mouth opening displacement (CMOD) control gave ~5% (statistically significant) variation over a very wide range of rates (1 to 80 µm/m/s), with the measurements being a function of rate. However, the rate effect was eliminated by use of dry nitrogen, implying a stress corrosion effect rather than a stability effect. With the use of a nitrogen environment during strain controlled tests, fracture toughness values were within about 1% over a wide range of rates (1 to 80 µm/m/s). CMOD or strain control did allow stable crack extension well past maximum force, and thus is preferred for energy calculations. The effort is being used to confirm recommendations in ASTM Test Method C1421 on fracture toughness measurement. [ABSTRACT FROM AUTHOR]

In this paper, we aim at determining the actual fracture toughness of three difference yttria concentrations (3 mol%, 5 mol% and 8 mol%) zirconia ceramics by single-edge V-notched beam (SEVNB) method. The notch root radius (ρ≈0.25 μm) introduced by femtosecond laser is smaller than the grain size of 3YSZ. As obtained K Ic values for the three zirconia samples are 4.4 ± 0.12, 2.8 ± 0.11 and 1.6 ± 0.05 MPa m 1/2 for 3YSZ, 5YSZ and 8YSZ, respectively. However, for a notch root radius of 9 µm cut by a razor blade, the K Ic value of 3YSZ is 6.2 ± 0.47 MPa m 1/2 . The volume fraction of m-ZrO 2 on fractured surface determined by XRD is found to be nearly equal to that of SENB method. Specifically, the load-deflection curves of SEVNB method under the loading rate of 0.05 mm/min, 0.03 mm/min and 0.01 mm/min exhibit a stable crack propagation behavior. [ABSTRACT FROM AUTHOR]

This paper is concerned with numerical modeling of deformation and fracture of a metal ligament bridging the crack faces in ceramic–metal composites, as a prerequisite for the determination of the J integral for composites with interpenetrating microstructure. A finite element model is proposed of an elasto-plastic crack-reinforcing fiber undergoing large plastic deformations and progressive debonding from the elastic matrix through a cohesive matrix–fiber interface. The σ-u relationships are derived first in the case of pullout of an elasto-plastic fiber embedded in an elastic matrix and then in uniaxial tension of the elasto-plastic fiber bridging the crack faces in elastic matrix. The obtained numerical results are discussed and compared with the theoretical predictions reported by other authors. [ABSTRACT FROM AUTHOR]

The results of a combined computational and experimental research into the fracture resistance of ceramic materials by specimen edge chipping are provided. The chipping was performed with conic diamond indenters that had spherical tip radii of 100, 200 and 400 μ m . The computational analysis was conducted on the basis of finite element modeling by means of ANSYS software. The parameters of the basic distances in an analysis of the stress, strain, and displacement fields in the chipping zone for the tests (upper and lower limit) have been established for the above-mentioned indenters in order to ensure the correct comparative assessment of the materials under research. Unified curves of edge chipping resistance of the ceramic materials have been obtained for the indenters with various spherical tip radii. [ABSTRACT FROM AUTHOR]

A cohesive element numerical model, which reproduces the three-dimensional microstructure of a 2.5-dimensional silicon-nitrogen-oxide fibre/fabric-reinforced boron nitride ceramic matrix composite (SiNO/BN) is applied to simulate the failure of specimens that are observed in situ during diametral compression testing. Measurements of deformation by image correlation of two-dimensional optical surface observations and three-dimensional X-ray computed tomographs are used to fit the simulation's elastic properties for the matrix and fibre tows. The observed patterns of damage nucleation and propagation are correctly simulated using a local tensile strain criterion. [ABSTRACT FROM AUTHOR]

It is difficult to observe the thermal shock cracking in real time, so the measurement of the crack after thermal shock is considered as an alternative method. This paper proposes a new experimental method which can exhibit the thermal shock cracking in real time by water quenching of translucent ceramic and high-speed imaging. The crack propagation is captured, and the crack growth rate is calculated. The results confirm the previous theoretical predictions of crack propagation under thermal shock. This paper expands the research on understanding the failure mechanisms of ceramic materials in thermal shock. [ABSTRACT FROM AUTHOR]

A model for the penetration of a ceramic target with the formation of an expanding conical hole is proposed that can be used to determine the apex angle of the cone knocked out from the target. The main cause of this fracture of ceramic targets is that the tensile strength of a ceramic material is much lower than its compressive strength. A method for calculating the maximum penetration velocity in a ceramic target without substrate was developed using the energy fracture criterion for ceramics. Two-dimensional numerical simulation of the impact of a steel projectile on a corundum plate showed satisfactory agreement between the calculated and experimental configurations of the resulting conical crack provided that the ratio between the compressive and tensile strengths corresponds to the recommendations of the developed model. [ABSTRACT FROM AUTHOR]

Aim: To evaluate the resistance to axial forces of screw-retained monolithic high translucency zirconia (mHTZr) crowns compared with high translucency zirconia + feldspathic ceramic (HTZrC) crowns, low translucency zirconia + feldspathic ceramic (LTZrC) crowns, and metal-ceramic (MC) crowns, and also to observe the different fracture patterns between all groups. Methods: Twenty-four crowns were fabricated (6 of each group) and loaded until failure, using a testing machine with a 5.0-kN load cell. Results: Mean fracture results varied between 1092.7 N (LTZrC group) and 3439.7 N (mHTZr group). No statistically significant differences were found between the HTZrC, LTZrC, and MC groups. However, statistically significant differences (P < 0.05) were found between mHTZr and the other 3 groups. In the MC group, only chipping of the ceramic veneering occurred. In the mHTZr group, when fracturing occurred, it was of the whole structure. Finally, the LTZrC and HTZrC groups suffered both chipping and core fractures. Conclusion: High translucency monolithic zirconia implant-supported crowns proved to be the toughest group studied when an axial force was applied. Fracture patterns varied between different materials, chipping being the most common occurrence. [ABSTRACT FROM AUTHOR]

We study a crack lying along an imperfect interface in an anisotropic bimaterial. A method is devised where known weight functions for the perfect interface problem are used to obtain singular integral equations relating the tractions and displacements for both the in-plane and out-of-plane fields. The problem can be considered as modelling bimaterial ceramics which are joined with a thin soft adhesive substance. The integral equations for the out-of-plane problem are solved numerically for orthotropic bimaterials with differing orientations of anisotropy and for different extents of interfacial imperfection. These results are then compared with finite element computations. [ABSTRACT FROM AUTHOR]

ZrN’s good thermal and mechanical properties make it suitable for many commercial applications including in nuclear fuels. An understanding of its oxidation behaviour is essential to prevent catastrophic failures and ensure it is employed safely in nuclear power plants. Based on available experimental results on oxidation of ZrN in the temperature range 1173–1373 K, a continuum damage mechanics-based combined creep and time-dependent material oxidation model is proposed. The model allows for the development of a surface oxide layer combined with damage due to creep under an applied load. A representative grain structure has been modelled according to ZrN microstructural characteristics in order to allow intergranular cracking and individual oxidation damage rates for grains and grain boundaries. The proposed damage model is implemented as a user subroutine and runs in a coupled temperature-displacement analysis using the commercial finite element software Abaqus. Available data on ZrN are used to validate the capability of the model to predict oxidation damage in ceramics at high temperatures. [ABSTRACT FROM AUTHOR]

A model for crack propagation along a non-locally pre-stressed interface in ceramic materials is studied. The problem is analysed on a discrete chain of oscillators, with local and non-local interactions. The pre-stressed state is defined by the stiffnesses of the non-local links. Small negative stiffnesses of such links reveals the existence of crack speeds supporting stable crack propagation, which is not possible in a structure which has only local interactions. [ABSTRACT FROM AUTHOR]

Experimental validation is provided for a linear elastic model describing the trajectory of a crack which propagates under Mode-I conditions in a ceramic sample, as influenced by non-interacting voids. A wide range of experiments were performed by quasi-static loading standard notched unglazed ceramic samples under pure Mode-I loading conditions. It is found that the predicted crack trajectories are in close agreement with the experimental results, so that the model is fully validated and therefore permits correct simulations of crack paths in brittle materials containing small voids. [ABSTRACT FROM AUTHOR]

Knowledge of crack initiation, propagation, and corresponding thermal shock failure evolution is prerequisite for effective maintenance of civil engineering so as to avoid disaster. Experimental analysis of the cracking in the ceramic sheets subsequent to water quenching has been conducted. Based on statistical mesoscopic damage mechanics, it was revealed that there are four stages in the process of thermal shock evolution of ceramics subjected to water quenching. The multiple cracks interaction mechanism has been analyzed from the viewpoint of the evolution of the elastic strain energy and stress intensity factor. [ABSTRACT FROM AUTHOR]

A tantalum carbide (TaC) ceramic layer was produced on gray cast iron matrix by in situ technique comprising a casting process and a subsequent heat treatment at 1135 °C for 45 min. Indentation fracture toughness in TaC ceramic layer was determined by the Vickers indentation test for various loads. A Niihara approach was chosen to assess the fracture toughness of TaC ceramic layer under condition of the Palmqvist mode in the experiment. The results reveal that K evaluation of TaC ceramic layer by the Vickers indentation method strongly depends on the selection of crack system and K equations. The critical indentation load for Vickers crack initiation in TaC ceramic layer lies between 1 and 2 N and the cracks show typical intergranular fracture characteristics. Indentation fracture toughness calculated by the indentation method is independent of the indentation load on the specimen. The fracture toughness of TaC ceramic layer is 6.63 ± 0.34 MPa m, and the toughening mechanism is mainly crack deflection. [ABSTRACT FROM AUTHOR]

The fracture toughness, K IC of two 3Y–ZrO 2 with different grain size (177 and 330 nm) and 12Ce–ZrO 2 were determined from a sharp micro-machined notch by Ultra-Short Pulsed Laser Ablation (UPLA) where a micro-cracked zone and non-transformed is generated in front of the notch. The notch plus the damage behaved as an unshielded edge surface crack. The fracture stress, σ f of both 330 nm-3Y–ZrO 2 and 12Ce–ZrO 2 with similar short crack sizes were found to be comparable in despite of their different published R -curves. The results of K IC were discussed in terms of the type of cracks induced and by using a simple R -curve model. It was concluded that for the development of high strength composites with 12Ce–ZrO 2 as the matrix, the relevant K IC that controls the σ f with surface unshielded short cracks is much closer to the intrinsic K IC than to the indentation K IC or to the plateau K IC of long cracks. [ABSTRACT FROM AUTHOR]

Metal/ceramic composites with lamellar microstructures are a novel class of metal-matrix composites produced by infiltration of freeze-cast or ice-templated ceramic preforms with molten aluminium alloy. The cost-effectiveness of production and relatively high ceramic content make such composites attractive to a number of potential applications in the automotive, aerospace and biomedical engineering. A hierarchical lamellar microstructure exhibited by these composites, with randomly orientated domains in which all ceramic and metallic lamellae are parallel to each other, is the result of the ice crystal formation during freeze-casting or ice-templating of preforms from water-ceramic suspensions. In this paper, a single-domain sample of metal/ceramic composite with lamellar microstructure is modelled theoretically using a combination of analytical and computational means. Stress field in the sample containing multiple transverse cracks in the ceramic layer is determined using a modified 2-D shear lag approach and a finite element method. Using finite element modelling, the shear layer thickness is determined and used as input in the analytical model. Degradation of stiffness properties of the sample due to multiple transverse cracking is predicted using the equivalent constraint model. [ABSTRACT FROM AUTHOR]

In this paper, we present results of a study of the generation of electromagnetic emission during impact loading of ZnS and ZnSe ceramics prepared by various techniques. The choice of the type of mechanical action is associated with the typical applications of these ceramics. Separate contributions to emission activity from the dislocations movement and the microcracks development depending on the crystallite size in the ceramics are shown. The electromagnetic emission is compared with parallel time series of pulses of mechanoluminescence and acoustic emission. In all three cases, emission activity was recorded with a time resolution of 10 ns. [ABSTRACT FROM AUTHOR]

Cylindrical and bamboo-like boron nitride nanotubes (BNNTs) have been used to reinforce brittle amorphous borosilicate glass matrix materials prepared by spark plasma sintering. The mechanical properties, such as hardness, Young's modulus, fracture toughness, and scratch resistance of the materials have been investigated. The fracture toughness of the composites showed an improvement of ~30% compared to the pure amorphous glass. BNNTs pull-out, crack bridging, stretching, and crack deflection toughening mechanisms were observed in the reinforced glass matrix composites. Extensive pull-out of the BNNTs (>400nm) was observed in the form of the telescopic "sword-in-sheath" mechanism, resulting in poor energy dissipation due to the weak Van der Waals force between the inner walls of the BNNTs. The scratch resistance was significantly improved (~26%) after the addition of the BNNTs, and the results correspond well with the brittleness index of the materials. [ABSTRACT FROM AUTHOR]

The influence of various rare-earth oxide additives and the addition of SiC nanoparticles on the thermal shock resistance of the Si3N4 based materials was investigated. The location of SiC particles inside the Si3N4 grains contributed to a higher level of residual stresses, which caused a failure at the lower temperature difference compared to the composites with a preferential location of the SiC at the grain boundaries. A critical temperature difference increased with an increasing ionic radius of RE3+ for both the composites and the monoliths. The critical temperature difference for the composite (580°C) and the monolith (680°C) sintered with La2O3 was significantly higher compared to the composite and the monolith doped with Lu2O3 (430°C). A good agreement was found between the results of the critical temperature difference estimated by the indentation quench test and that obtained by the strength retention method. [ABSTRACT FROM AUTHOR]

Si3N4 based composites with 7wt.% of graphene nanoplatelets (GNPs) were prepared using different homogenization methods. Si3N4/GNPs powder mixtures were dispersed in isopropanol and homogenized by attritor milling, ball milling or planetary ball milling. The ball milling technique was also used for the homogenization of Si3N4/GNPs mixture in dry state. Fractography analysis was carried out in order to assess the individual homogenization treatment. Depending on the homogenization methods, the size of the processing flaws varied from 20µm up to 400µm. The agglomeration of the GNPs and the residual porosity were found as the most frequently observed types of the critical flaws. The planetary ball milling with previous ultrasonication of GNPs in isopropanol was found to be the most promising homogenization technique, resulting in the composites with the highest bending strength (average value is 740MPa) and the lowest average size of the processing flaws (around 20µm). [ABSTRACT FROM AUTHOR]

The uniaxial tensile stress-strain behavior of three porous ceramic materials was determined at ambient conditions. Test specimens in the form of thin beams were obtained from the walls of diesel particulate filter honeycombs and tested using a microtesting system. A digital image correlation technique was used to obtain full-field 2D in-plane surface displacement maps during tensile loading, and in turn, the 2D strains obtained from displacement fields were used to determine the Secant modulus, Young's modulus, and initial Poisson's ratio of the three porous ceramic materials. Successive unloading-reloading experiments were performed at different levels of stress to decouple the linear elastic, anelastic, and inelastic response in these materials. It was found that the stress-strain response of these materials was nonlinear and that the degree of nonlinearity is related to the initial microcrack density and evolution of damage in the material. [ABSTRACT FROM AUTHOR]

Introduction: In this study, we present the short-term results of the Selexys TH+ cup with the Ceramys inlay which is a press-fit cup with a ceramic-on-ceramic articulation. (Mathys, Bettlach, Switzerland). We compared the results with a retrospective-matched control group with a Delta PF cup (Lima, Udine, Italy), which is also a press-fit cup with a ceramic-on-ceramic articulation. Materials and methods: 257 elective hip arthroplasties with the Selexys TH+ cup in 250 patients placed in 2009 and 2010 were analyzed and compared with a control group retrospective analysis of the uncemented Delta PF cup (Lima, Udine, Italy) placed in 2007 and 2008 in 208 patients (222 hips). Surgical technique and surgeons were identical in both groups. Results: During a follow-up period of 3–21 months, 19 aseptic loosenings (7.4 %) were found for the Selexys TH+ cup. The survival plotted by a Kaplan–Meier curve shows a 1-year survival of 87.4 %. The Lima Delta PF cup showed a 1-year survival of 99.5 %. Failure analysis showed no clear explanation for this early loosening. Conclusion: The Selexys TH+ cup combined with the Ceramys ceramic-on-ceramic inlay coupling show an unacceptable high early revision rate. Therefore, we advice against using this combination. [ABSTRACT FROM AUTHOR]

Shape memory materials are a class of smart materials able to convert heat into mechanical strain (or strain into heat) by virtue of a martensitic phase transformation. Some brittle materials such as intermetallics and ceramics exhibit a martensitic transformation but fail by cracking at low strains and after only a few applied strain cycles. Here we show that such failure can be suppressed in normally brittle martensitic ceramics by providing a fine-scale structure with few crystal grains. Such oligocrystalline structures reduce internal mismatch stresses during the martensitic transformation and lead to robust shape memory ceramics that are capable of many superelastic cycles up to large strains; here we describe samples cycled as many as 50 times and samples that can withstand strains over 7%. Shape memory ceramics with these properties represent a new class of actuators or smart materials with a set of properties that include high energy output, high energy damping, and high-temperature usage. [ABSTRACT FROM AUTHOR]

This study investigated the influence of the elastic modulus of supporting dies on the fracture strengths of all-ceramic materials used in dental crowns. Four different types of supporting die materials (dentin, epoxy resin, brass, and stainless steel) (24 per group) were prepared using a milling machine to simulate a mandibular molar all-ceramic core preparation. A total number of 96 zirconia cores were fabricated using a CAD/CAM system. The specimens were divided into two groups. In the first group, cores were cemented to substructures using a dual-cure resin cement. In the second group, cores were not cemented to the supporting dies. The specimens were loaded using a universal testing machine at a crosshead speed of 0.5 mm/min until fracture occurred. Data were statistically analyzed using two-way analysis of variance and Tukey HSD tests ( α = 0.05). The geometric models of cores and supporting die materials were developed using finite element method to obtain the stress distribution of the forces. Cemented groups showed statistically higher fracture strength values than non-cemented groups. While ceramic cores on stainless steel dies showed the highest fracture strength values, ceramic cores on dentin dies showed the lowest fracture strength values among the groups. The elastic modulus of the supporting die structure is a significant factor in determining the fracture resistance of all-ceramic crowns. Using supporting die structures that have a low elastic modulus may be suitable for fracture strength tests, in order to accurately reflect clinical conditions. [ABSTRACT FROM AUTHOR]

Abstract: Laminated SiC/ZrB2 ceramic was fabricated by roll-compaction and spark plasma sintering at 1600°C. A maximum fracture toughness of 12.3±0.3MPam1/2 was measured for the sintered SiC/ZrB2 laminated ceramic. This significant improvement in fracture toughness can be attributed to the crack deflection along the interfacial layer and the presence of residual stresses in the sample. The effect of interlayer composition on the residual stresses was discussed in detail. It is observed that the residual thermal stress could be reduced by addition of ZrB2 particles to the SiC interlayer. The bending strength can be increased to 388±44MPa with the addition of 20vol% ZrB2 to the SiC interlayer. [Copyright &y& Elsevier]

Abstract: The Weibull distribution is the most widely used function in the reliability analysis and structural design of dental ceramics; however, it is still unclear whether Weibull distribution is always the most suitable one. With wide applications of dental ceramics, a special attention has been paid in discriminating their strength distributions. In this paper, three versatile functions, involving normal, log-normal and Weibull distributions, are applied to the analysis of ten strength data sets of dental ceramics with different compositions and the results are compared in terms of the Akaike information criterion and the Anderson–Darling test. It reveals that various microstructures and compositions in the investigated dental ceramics cause their strength distributions deviated from the Weibull distribution. The influence of microstructure induced fracture properties (multiple-modal flaw size distribution, R-curve behavior and subcritical crack growth) on strength distributions is discussed. [Copyright &y& Elsevier]

Abstract: Fracture toughness, four-point bending strength of transparent spinel, Y2O3 and YAG ceramics in function of temperature (from room temperature up to 1500°C) were measured. Creep resistance at 1500–1550°C was studied too. Grain size distribution was determined on polished and etched surfaces of samples. Fracture surfaces after tests were examined by scanning electron microscopy. The obtained results showed that: in the case of spinel ceramics fracture toughness and strength decreased from 20 to 800°C, increased from 800 to 1200°C and decreased at higher temperature; in the case of Y2O3 ceramics they increased from 400 to 800°C, and next kept constant up to 1500°C; in the case of YAG ceramics they kept constant from 20 to 1200°C and then decreased. The creep strain rate was measured for spinel and YAG but not for Y2O3 ceramics which appeared creep resistant. The hypotheses concerning toughening and creep mechanisms were proposed. [Copyright &y& Elsevier]

High temperature flexural strength of ZrB2-20 vol% SiC ceramics ( ZS) up to 1600°C in high purity argon atmosphere was significantly improved by adding 5 vol% WC, but degraded when 5 vol% ZrC was added. ZrB2-20 SiC-5 WC ceramic ( ZSW) has a very high strength (mean ± SD) of 675 ± 33 MPa at 1600°C, and also an elastic and transgranular fracture mode was observed. According to the analysis of the fracture modes and crack origins in ZSW ceramics, the improvement in strength above 1000°C was attributed to the removal of the oxide impurities from grain boundaries. [ABSTRACT FROM AUTHOR]

Abstract: “Nothing worthwhile is ever without complications.” Nora Roberts The recent increase in reports from clinical studies of ceramic chipping has raised the question of which criteria should constitute success or failure of total-ceramic prostheses. Terminologies such as minor chipping , partial chipping, technical complications , and biological complications have crept into the dental terminology and they have complicated our classification of success and failure of these crown and bridge restorations. Some journals have permitted the reporting of fractures as “complications” and they are not necessarily classified as failures in the study. One study has attempted to classify chipping fractures according to their severity and subsequent treatment . This is a promising approach to resolve the challenges to the classification of chipping fracture. The term ‘chipping fracture’ is more descriptive than ‘chipping’ since the latter term tends to imply an event of minor consequence. Two types of statistics are reported routinely in these studies, i.e., percent success, which is a measure of restorations that survive without any adverse effects, and percent survival, which is a measure of all restorations that survive even though they may have exhibited chipping fracture or they may have been repaired. Why has this scenario occurred? One possible explanation is that many of these types of fractures are very small and do not affect function or esthetics. Another reason is that corporate sponsors prefer to use the term chipping since it does not connote failure in the sense that the term fracture does. In any event, we need to be more precise in our scientific observations of fracture and classifications of the various types of fracture including details on the location of fracture and the prosthesis design configuration. Because of the lack of standardized methods for describing chipping fractures, materials scientists are unable to properly analyze the effect of material properties and design factors on the time-dependent survival probability of ceramic fixed dental prostheses (FDPs). Based on the review of clinical trials and systematic reviews of these trials, the present study was designed to develop guidelines for classifying the functional performance, success, survival, and susceptibility to chipping fracture, and subsequent treatment of ceramic and metal–ceramic restorations. Objective: To develop comprehensive descriptive guidelines and a clinical reporting form to assist dental scientists in their analyses of chipping fracture behavior of metal–ceramic and all-ceramic prostheses with particular emphasis on veneered-zirconia restorations. These guidelines are required to optimize the recording of fracture features that can be used to differentiate ceramic chipping fracture from bulk fracture and to assist dentists in identifying subsequent treatment that may minimize the need to replace affected restorations. A recording form for clinical fracture observations must be sufficiently clear and complete so that dental health professionals can translate the most relevant information in a context that allows their patients to fully understand the potential risks and benefits of treatment with ceramic restorations. It should clearly allow a clinician to determine whether or not a ceramic fracture constitutes a failure, which requires replacement of the prosthesis, or whether the fracture surface is relatively small or located in a nonfunctional area, i.e., one that is not contribute to occlusion, esthetics, proximal contacts, or food impaction. To accomplish this task, a review of the relevant publications of clinical trials was necessary to identify the variability in reporting of fracture events. The reviews were focused on clinical research studies of zirconia-based FDPs and PFM FDPs, which had been monitored through recall exams for three years or more. These reports and systematic reviews of all relevant publications were published in English dental journals between 2004 and 2010.The primary focus in this review was on the susceptibility to chipping fracture or bulk fracture of veneered zirconia-based fixed dental prostheses (FDPs) and metal–ceramic FDPs, which are also referred to in this paper as porcelain-fused-to-metal (PFM) FDPs. [Copyright &y& Elsevier]

Experimental data on the determination of the creep rupture strength (time and strain to rupture) of densely sintered periclase ceramic at temperatures to 1600°C under loads 20 - 50 MPa are presented. It is shown that the durability of materials can be determined from measurements of the rate of steady creep below the rupture level. [ABSTRACT FROM AUTHOR]