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The present work aims to develop a production method of pre-sintered zirconia-toughened-alumina (ZTA) composite blocks for machining in a computer-aided design and computer-aided manufacturing (CAD-CAM) system. The ZTA composite comprised of 80% Al 2 O 3 and 20% ZrO 2 was synthesized, uniaxially and isostatically pressed to generate machinable CAD-CAM blocks. Fourteen green-body blocks were prepared and pre-sintered at 1000 °C. After cooling and holder gluing, a stereolithography (STL) file was designed and uploaded to manufacture disk-shaped specimens projected to comply with ISO 6872:2015. Seventy specimens were produced through machining of the blocks, samples were sintered at 1600 °C and two-sided polished. Half of the samples were subjected to accelerated autoclave hydrothermal aging (20h at 134 °C and 2.2 bar). Immediate and aged samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Optical and mechanical properties were assessed by reflectance tests and by biaxial flexural strength test, Vickers indentation and fracture toughness, respectively. Samples produced by machining presented high density and smooth surfaces at SEM evaluation with few microstructural defects. XRD evaluation depicted characteristic peaks of alpha alumina and tetragonal zirconia and autoclave aging had no effect on the crystalline spectra of the composite. Optical and mechanical evaluations demonstrated a high masking ability for the composite and a characteristic strength of 464 MPa and Weibull modulus of 17, with no significant alterations after aging. The milled composite exhibited a hardness of 17.61 GPa and fracture toughness of 5.63 MPa m 1/2 , which remained unaltered after aging. The synthesis of ZTA blocks for CAD-CAM was successful and allowed for the milling of disk-shaped specimens using the grinding method of the CAD-CAM system. ZTA composite properties were unaffected by hydrothermal autoclave aging and present a promising alternative for the manufacture of infrastructures of fixed dental prostheses., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Objective: To investigate the effect of ceramic thickness and dental substrate (enamel vs. dentin/enamel) on the survival rate and failure load of non-retentive occlusal veneers., Materials and Methods: Human maxillary molars (n = 60) were divided into five test-groups (n = 12). The groups (named DE-1.5, DE-1.0, DE-0.5, E-1.0, E-0.5) differed in their dental substrate (E = enamel, DE = dentin/enamel) and restoration thickness (standard: 1.5 mm, thin: 1.0 mm, ultrathin: 0.5 mm). All teeth were prepared for non-retentive monolithic lithium-disilicate occlusal veneers (IPS e.max Press, Ivoclar). Restorations were adhesively cemented (Syntac Classic/Variolink II, Ivoclar) and exposed to thermomechanical fatigue (1.2 million cycles, 1.6 Hz, 49 N/ 5-55°C). Single load to failure was performed using a universal testing-machine. A linear-regression model was applied, pairwise comparisons used the Student-Newman-Keuls method (p < 0.05)., Results: Three dentin-based occlusal veneers (one DE-1.0, two DE-0.5) revealed cracks after fatigue exposure, which corresponds to an overall-survival rate of 95%. Load to failure resulted in the following ranking: 2142 N(DE-0.5) > 2105 N(E-1.0) > 2075 N(E-0.5) > 1440 N(DE-1.5) > 1430 N(DE-1.0). Thin (E-1.0) and ultrathin enamel-based occlusal veneers (E-0.5) revealed high failure loads and surpassed the standard thickness dentin-based veneers (DE-1.5) significantly (p = 0.044, p = 0.022)., Conclusion: All tested monolithic lithium disilicate occlusal veneers obtained failure loads above physiological chewing forces. Thin and ultrathin enamel-based occlusal veneers outperformed the standard thick dentin-based occlusal veneers., Clinical Significance: Minimally invasive enamel-based occlusal veneer restorations with non-retentive preparation design may serve as a conservative treatment option., (© 2023 The Authors. Journal of Esthetic and Restorative Dentistry published by Wiley Periodicals LLC.)

Objective: The background and clinical understanding of the properties of currently available indirect restorative systems and fabrication methods is, along with manufacturer and evidence-based literature, an important starting point to guide the clinical selection of materials for tooth and/or implant supported reconstructions. Therefore, this review explores most indirect restorative systems available in the market, especially all-ceramic, along with aspects of manufacturing process, clinical survival rates, and esthetic outcomes., Overview: Progressive incorporation of new technologies in the dental field and advancements in materials science have enabled the development/improvement of indirect restorative systems and treatment concepts in oral rehabilitation, resulting in reliable and predictable workflows and successful esthetic and functional outcomes. Indirect restorative systems have evolved from metal ceramics and polymers to glass ceramics, polycrystalline ceramics, and resin-matrix ceramics, aiming to improve not only biological and mechanical properties, but especially the optical properties and esthetic quality of the reconstructions, in attempt to mimic natural teeth., Conclusions: Based on several clinical research, materials, and patient-related parameters, a decision tree for the selection of indirect restorative materials was suggested to guide clinicians in the rehabilitation process., Clinical Significance: The pace of materials development is faster than that of clinical research aimed to support their use. Since no single material provides an ideal solution to every case, professionals must continuously seek information from well designed, long-term clinical trials in order to incorporate or not new materials and technological advancements., (© 2023 Wiley Periodicals LLC.)

Objectives: To characterize the optical and mechanical properties of a commercial and in-house translucent Y-TZP before and after aging in autoclave or hydrothermal reactor., Methods: In-house experimental discs were obtained through uniaxial and isostatic pressing a translucent Y-TZP powder and sintering at 1,550 °C/1 h. Commercial discs were milled from pre-sintered blocks fabricated with the same powder through uniaxial and isostatic pressing and sintering. Discs were allocated into three groups according to aging condition: immediate, aged via autoclave, or reactor (134 °C, 20 h, 2.2 bar). Crystalline content and microstructure were evaluated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Residual compressive stress (CS) was determined by Raman spectroscopy. Optical properties were determined by the contrast ratio (CR) and translucency parameter (TP) using reflectance data. Mechanical properties were assessed by Vickers hardness, fracture toughness and biaxial flexural strength tests., Results: XRD and SEM revealed a typical Y-TZP crystalline content, chiefly tetragonal phase, and a dense crystalline matrix for both processing protocols. Reactor aging triggered a more pronounced t-m transformation relative to autoclave. In-house and commercial Y-TZPs demonstrated similar CR and TP, with reactor aging significantly increasing their translucency. Similarly, reactor aging influenced Vickers hardness and fracture toughness. In-house processed Y-TZP clearly demonstrated the presence of CS, whereas commercial Y-TZP showed no presence of CS. Non-aged in-house Y-TZP resulted in significantly lower characteristic strength relative to commercial Y-TZP. While aging protocols significantly increased the characteristic strength of in-house Y-TZP, reactor significantly decreased commercial Y-TZP characteristic strength. Both Y-TZP processing protocols demonstrated high reliability at high-stress missions, with no detrimental effect of aging., Conclusions: Laboratory aging methodology significantly influenced optical and mechanical properties of a commercial and in-house translucent Y-TZP., (Copyright © 2020. Published by Elsevier Ltd.)

Objectives: Controversy exists about whether the elastic modulus (E) mismatch between the loading indenter and ceramic materials influences fatigue testing results. The research hypotheses were that for porcelain veneered Y-TZP crowns 1) A low modulus Steatite indenter (SB) leads to higher fatigue reliability compared to a high modulus tungsten carbide indenter (WC); 2) Different surface damage patterns are expected between low and high modulus indenters after sliding contact fatigue testing. All ceramic crowns will exhibit similar step-stress accelerated life testing (SSALT) contact fatigue reliability (hypothesis 1) and failure characteristics (hypothesis 2) when using high stiffness tungsten carbide (WC, E = 600 GPa) vs. enamel like steatite (SB, E = 90 GPa) indenters., Methods: Manufacturer (3M Oral Care) prepared Y-TZP-veneered all-ceramic molar crowns were bonded to aged resin composite reproductions of a standard tooth preparation and subjected to mouth-motion SSALT fatigue (n = 18 per indenter type). Failure was defined either as initial inner cone crack (IC), or final fracture (FF) when porcelain fractured (chipping). Selected IC specimens that did not progress to FF were embedded in epoxy resin and sectioned for fractographic analysis., Results: The distribution of failures across the load and cycle profiles lead to similar calculated Weibull Use Level Probability Plots with overlap of the 2-sided 90% confidence bounds. The calculated reliability for IC and FF was equivalent at a mission of 300 N or 700 N load and 50,000 cycles, although the WC indenter had a trend for lower reliability for IC at 700 N. Both indenters produced similar patterns of wear and cracking on crown surfaces. Fractographic landmarks showed competing failure modes, but sliding contact partial inner cone cracks were the most dominant for both groups., Significance: The more compliant Steatite indenter had similar veneered crown fatigue reliability and failure modes to those found with use of a high stiffness tungsten carbide indenter (hypotheses 1 and 2 rejected)., Competing Interests: Declaration of competing interest No conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Objectives: To evaluate the probability of survival and failure modes of implant-supported resin nanoceramic relative to metal-ceramic crowns., Methods: Resin nanoceramic molar crowns (LU) (Lava Ultimate, 3M ESPE, USA) were milled and metal-ceramic (MC) (Co-Cr alloy, Wirobond C+, Bego, USA) with identical anatomy were fabricated (n=21). The metal coping and a burnout-resin veneer were created by CAD/CAM, using an abutment (Stealth-abutment, Bicon LLC, USA) and a milled crown from the LU group as models for porcelain hot-pressing (GC-Initial IQ-Press, GC, USA). Crowns were cemented, the implants (n=42, Bicon) embedded in acrylic-resin for mechanical testing, and subjected to single-load to fracture (SLF, n=3 each) for determination of step-stress profiles for accelerated-life testing in water (n=18 each). Weibull curves (50,000 cycles at 200N, 90% CI) were plotted. Weibull modulus (m) and characteristic strength (η) were calculated and a contour plot used (m versus η) for determining differences between groups. Fractography was performed in SEM and polarized-light microscopy., Results: SLF mean values were 1871N (±54.03) for MC and 1748N (±50.71) for LU. Beta values were 0.11 for MC and 0.49 for LU. Weibull modulus was 9.56 and η=1038.8N for LU, and m=4.57 and η=945.42N for MC (p>0.10). Probability of survival (50,000 and 100,000 cycles at 200 and 300N) was 100% for LU and 99% for MC. Failures were cohesive within LU. In MC crowns, porcelain veneer fractures frequently extended to the supporting metal coping., Conclusion: Probability of survival was not different between crown materials, but failure modes differed., Significance: In load bearing regions, similar reliability should be expected for metal ceramics, known as the gold standard, and resin nanoceramic crowns over implants. Failure modes involving porcelain veneer fracture and delamination in MC crowns are less likely to be successfully repaired compared to cohesive failures in resin nanoceramic material., (Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Classification systems for all-ceramic materials are useful for communication and educational purposes and warrant continuous revisions and updates to incorporate new materials. This article proposes a classification system for ceramic and ceramic-like restorative materials in an attempt to systematize and include a new class of materials. This new classification system categorizes ceramic restorative materials into three families: (1) glass-matrix ceramics, (2) polycrystalline ceramics, and (3) resin-matrix ceramics. Subfamilies are described in each group along with their composition, allowing for newly developed materials to be placed into the already existing main families. The criteria used to differentiate ceramic materials are based on the phase or phases present in their chemical composition. Thus, an all-ceramic material is classified according to whether a glass-matrix phase is present (glass-matrix ceramics) or absent (polycrystalline ceramics) or whether the material contains an organic matrix highly filled with ceramic particles (resin-matrix ceramics). Also presented are the manufacturers' clinical indications for the different materials and an overview of the different fabrication methods and whether they are used as framework materials or monolithic solutions. Current developments in ceramic materials not yet available to the dental market are discussed.

Several all-ceramic systems have been developed in dentistry to meet the increased expectations of patients and dentists for highly aesthetic, biocompatible, and long-lasting restorations. However, early bulk fractures or chippings have led the research community to investigate the mechanical performance of the all-ceramic systems. This overview explores the current knowledge of monolithic and bilayer dental all-ceramic systems, addressing composition and processing mechanisms, laboratory and clinical performance, and possible future trends for all-ceramic materials., (Copyright © 2011 Elsevier Inc. All rights reserved.)

In a crown system, core fracture requires replacement of the restoration. Understanding maximum principal stress concentration in the veneered core of a tooth-crown system as a function of variations in clinically relevant parameters is crucial in the rational design of crown systems. This study evaluated the main and interacting effects of a set of clinical variables on the maximum principal stress (MPS) in the core of an anatomically correct veneer-core-cement-tooth model. A 3D CAD model of a mandibular first molar crown was generated; tooth preparation was modeled by reducing the proximal walls by 1.5 mm and the occlusal surface by 2.0 mm. A cemented veneered core crown was modeled on the preparation. This "crown system" permitted finite element model investigation of the main and interacting effects of proximal wall height reduction, core material, core thickness, cement modulus, cement thickness, and load position on the maximum stress distribution in a factorial design. Analysis of variance was used to identify the main and interacting influences on the level of MPS in the crown core. Statistical significance was set at p<0.05. MPS levels varied as a function of two-way interactions between the following: core thickness and load position; cement thickness and load position; cement modulus and load position; cement thickness and core thickness; and cement thickness and cement modulus; and also three-way interactions among the load position, core material, and proximal wall height reduction, and among the core thickness, cement thickness, and cement modulus. MPS in the crown-tooth system is influenced by the design parameters and also by the interaction among them. Hence, while the geometry of molar crowns is complex, these analyses identify the factors that influence MPS and suggest levels that will minimize the core MPS in future studies of crown design.

The aim of this study was to evaluate the effect of two finishing techniques, glazing or polishing, in comparison with the as‐cut condition, on the biaxial‐flexural‐strength (BFS) of a zirconia‐reinforced lithium silicate ceramic (ZLS). Cylinders were milled from CAD/CAM blocks and sliced to obtain disc‐shaped specimens (ISO6872:2015). Polished and glazed specimens were processed following the manufacturer's instructions. Thirty‐three specimens were obtained for each condition and microstructural and BFS/fractographic characterizations were performed. BFS and roughness data were analyzed using Weibull statistics and ANOVA one‐way with Tukey post‐hoc test, respectively. While a rougher surface was observed for as‐cut specimens, smoother surfaces were observed for polished and glazed ZLS at microscopical evaluation and confirmed through surface‐roughness evaluation. X‐ray spectra depicted a glass phase for all groups and characteristic metasilicate, lithium disilicate, and lithium phosphate peaks for the as‐cut and polished specimens. Glazed specimens showed higher characteristic strength than polished and as‐cut specimens, which did not differ significantly. While higher Weibull‐modulus was observed for the polished than for the as‐cut specimens, no statistically significant differences were noted between glazed and polished, and between glazed and as‐cut specimens. ZLS presents higher strength when glazed, and polishing increases the structural reliability of the material relative to the as‐cut condition. Both finishing techniques reduced surface roughness similarly. [ABSTRACT FROM AUTHOR]

Background and Objectives: There are limited data regarding the behavior of resin matrix ceramics for current CAD-CAM materials. Further studies may be beneficial and can help clinicians planning to use these materials during prosthodontic rehabilitation. The aim of this study was to evaluate and compare the flexural strength and strain distributions, filler content, wear, and reliability of two resin matrix ceramic CAD-CAM materials. Materials and Methods: Two resin matrix ceramics, Ambarino High-Class (AH) and Vita Enamic (VE), were tested for flexural strength (n = 24), wear (n = 10), and reliability (n = 18). Thermogravimetric analysis was used to determine the percentage of filler by weight, and digital image correlation (DIC) was used for strain analysis in flexural strength test. Reliability of each resin matrix ceramic was compared after accelerated lifetime testing of crowns using a two-parameter Weibull distribution. Data of flexural strength, wear, and thermogravimetry were analyzed by independent t-tests with significance level at 5%. Results: The results of DIC analysis were analyzed by a qualitative comparison between the images obtained. The materials tested showed different flexural strength (p < 0.05) and strain distributions. The filler content was the same as informed by manufacturers. No difference was observed in the wear or reliability analysis (p > 0.05). The flexural strength of material AH was superior to VE, and the strain distribution was compatible with this finding. Conclusions: The two resin matrix ceramics tested showed similar behavior in wear and reliability analysis. Both can provide safe use for dental crowns. [ABSTRACT FROM AUTHOR]

No evidence-based prosthetic treatment concept for 3-unit fixed-dental-prostheses (FDPs) on ceramic implants is currently available. Therefore, the aim of this in vitro study was to investigate the failure load and fatigue behavior of monolithic and bi-layer zirconia FDPs supported by one-piece ceramic implants. Eighty 3-unit FDPs supported by 160 zirconia-implants (ceramic.implant; vitaclinical) were divided into 4 groups (n = 20 each): Group Z-HT: 3Y-TZP monolithic-zirconia (Vita-YZ-HT); Group Z-ST: 4Y-TZP monolithic-zirconia (Vita-YZ-ST); Group FL: 3Y-TZP zirconia (Vita-YZ-HT) with facial-veneer (Vita-VM9); Group RL (Rapid-layer): PICN "table-top" (Vita-Enamic), 3Y-TZP-framework (Vita-YZ-HT). Half of the test samples (n = 10/group) were fatigued in a mouth-motion chewing-simulator (F = 98 N, 1.2 million-cycles) with simultaneous thermocycling (5–55 °C). All specimens (fatigued and non-fatigued) were afterwards exposed to single-load-to-failure-testing (Z010, Zwick). Statistical analysis was performed using ANOVA, Tukey's post-hoc tests and two-sample t-tests (p < 0.05, Bonferroni-corrected where appropriate). All specimens withstood fatigue application. While the effect of fatigue was not significant in any group (p = 0.714), the choice of material had a significant effect (p < 0.001). Material FL recorded the highest failure loads, followed by Z-ST, Z-HT and RL, both with and without fatigue application. Taken together, all tested FDP material combinations survived chewing forces that exceeded physiological levels. Bi-Layer FL and monolithic Z-ST showed the highest resilience and might serve as reliable prosthetic reconstruction concepts for 3-unit FDPs on ceramic implants. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effect of ceramic thicknesses, bonding surface (enamel vs. dentin), and preparation design (box vs. no box) on the fatigue survival and failure load of minimally invasive full‐veneer restorations. Materials and Methods: Human‐premolars (n = 60) were divided into five test groups (n = 12). All teeth received full‐veneer preparation with the following occlusal/labial thicknesses: standard: 1.5/0.8 mm; thin: 1.0/0.6 mm; ultrathin 0.5/0.4 mm. Preparations for each ceramic thickness were refined in enamel (E‐1.0 and E‐0.5) or dentin (D‐1.5, D‐1.0, and D‐0.5). Control groups DB‐1.5, EB‐1.0, and EB‐0.5 received box preparations. Monolithic lithium disilicate restorations (IPS‐e.max‐Press, Ivoclar Vivadent) were adhesively cemented (Syntac‐Classic/Variolink‐II, Ivoclar Vivadent) and subjected to cyclic mechanical loading (F = 49 N, 1.2 million cycles) with simultaneous thermocycling (5–55°C). All specimens were exposed to single load‐to‐failure. Pair‐wise differences were calculated by using a linear regression model and Student–Newman–Keuls method (p < 0.05). Results: All full‐veneers of group D‐1.5, E‐1.0, E‐0.5, DB‐1.5, EB‐1.0, and EB‐0.5 survived fatigue. Two full‐veneers (D‐1.0 and D‐0.5) revealed cracks during fatigue, resulting in an overall fatigue survival rate of 98.1%. Mean load‐to‐failure values (N) were as followed: 1005 (D‐1.5); 866 (D‐1.0); 816 (D‐0.5); 1495 (E‐1.0); 1279 (E‐0.5); 1129 (DB‐1.5); 1087 (EB‐1.0); and 833 (EB‐0.5). Irrespective of ceramic thicknesses, enamel‐based full‐veneers resulted in higher failure loads than dentin‐based restorations. Box preparation reduced the failure loads of thin and ultrathin enamel‐based restorations. Conclusion: All tested monolithic lithium disilicate full‐veneer restorations exceeded physiological masticatory forces. Minimally invasive full‐veneer restorations with enamel as a bonding surface and a non‐retentive preparation design showed superior performance. Clinical Significance: Enamel‐based non‐retentive full‐veneers made of monolithic lithium disilicate may serve as a reliable and esthetical minimally invasive treatment option for premolars. [ABSTRACT FROM AUTHOR]

PURPOSE. The objective of this study was to evaluate the effect of thickness reduction and fatigue on the failure load of monolithic zirconia crowns. MATERIALS AND METHODS. 140 CAD-CAM fabricated crowns (3Y-TZP, inCorisTZI, Dentsply-Sirona) with different ceramic thicknesses (2.0, 1.5, 1.0, 0.8, 0.5 mm, respectively, named G2, G1.5, G1, G0.8, and G0.5) were investigated. Dies of a mandibular first molar were made of composite resin. The zirconia crowns were luted with a resin composite cement (RelyX Unicem 2 Automix, 3M ESPE). Half of the specimens (n = 14 per group) were mouth-motion-fatigued (1.2 million cycles, 1.6 Hz, 200 N/5 - 55°C, groups named G2-F, G1.5-F, G1-F, G0.8-F, and G0.5-F). Single-load to failure was performed using a universal testing-machine. Fracture modes were analyzed. Data were statistically analyzed using a Weibull 2-parameter distribution (90% CI) to determine the characteristic strength and Weibull modulus differences among the groups. RESULTS. Three crowns (21%) of G0.8 and five crowns (36%) of G0.5 showed cracks after fatigue. Characteristic strength was the highest for G2, followed by G1.5. Intermediate values were observed for G1 and G1-F, followed by significantly lower values for G0.8, G0.8-F, and G0.5, and the lowest for G0.5-F. Weibull modulus was the lowest for G0.8, intermediate for G0.8-F and G0.5, and significantly higher for the remaining groups. Fatigue only affected G0.5-F. CONCLUSION. Reduced crown thickness lead to reduced characteristic strength, even under failure loads that exceed physiological chewing forces. Fatigue significantly reduced the failure load of 0.5 mm monolithic 3Y-TZP crowns. [ABSTRACT FROM AUTHOR]

To characterize the physicomechanical properties of an alumina‐toughened zirconia (ATZ). ATZ synthesis consisted of the addition of alumina particles in an yttria‐stabilized tetragonal zirconia polycrystals (3Y‐TZP) matrix. Specimens were obtained by uniaxial and isostatic pressing ATZ and 3Y‐TZP powders and sintering at 1600°C/1 h and 1550°C/1 h, respectively. Crystalline content and residual stress were evaluated using X‐ray diffraction (XRD). Microstructure was characterized by scanning electron microscopy (SEM). Optical properties were determined by reflectance test. Mechanical properties were assessed by biaxial flexural strength test. All analyses were performed before and after aging (134°C, 20 h, 2 bar). XRD and SEM revealed a typical ATZ and 3Y‐TZP crystalline content, chiefly tetragonal phase, with a dense polycrystalline matrix, though a smaller grain size for ATZ. Aging triggered a similar monoclinic transformation for both systems; however, ATZ exhibited higher residual compressive stresses than 3Y‐TZP. While as‐processed 3Y‐TZP demonstrated significantly higher characteristic strength relative to ATZ, no significant difference was observed after aging (~215 MPa increase in the ATZ strength). ATZ presented significantly higher opacity relative to 3Y‐TZP, although aging significantly increased the translucency of both systems (increase difference significantly higher in the 3Y‐TZP compared to ATZ). ATZ physicomechanical properties support its applicability in the dental field, with a lower detrimental effect of aging relative to 3Y‐TZP. [ABSTRACT FROM AUTHOR]

The article focuses on real challenge in tooth reconstructions mainly involving periodontally and endodontically sound dentitions is to define how the interplay between the new ceramic materials properties along with handling by dentist and dental technician. Topics include improving the successful adhesion to glass-matrix ceramics will always open research field, and etching concentrations on the optical and physical properties of different ceramics to the microstructure and thicknesses.

Zirconia multilayer presents promising prospects, but there is scarce information about its microstructural and mechanical characterization. Therefore, this study sought to produce them in-house and to perform their characterization by comprising four groups of specimens to assess the biaxial flexural strength, microhardness, fracture toughness, phase characterization and quantification, fractography, and microstructural features. Weibull analysis was performed to determine the Weibull modulus and characteristic strength. The results showed that bilayers 3YSZ and 5YSZ presented intermediate mechanical properties when compared to 3YSZ and 5YSZ monolithic controls (680 MPa, 464 MPa, 885 MPa, 594 MPa, respectively). Fractographic analysis revealed that the failure origin was not at the interface in the bilayer groups, but residual stress was present between the layers. Hardness and fracture toughness were not affected by the interface. • In-house zirconia bilayers were produced to mimic real-use configuration. • Mechanical performance of bilayer zirconia varied according to layer configuration. • Monolithic zirconia outperformed the mechanical properties of bilayer systems. • Residual stresses in the interfaces of bilayer systems were characterized. • Failures originated from surface flaws, but different propagation patterns existed. [ABSTRACT FROM AUTHOR]

Abstract: Purpose: A ceramic and metal abutment prototype was fatigue tested to determine the probability of survival at various loads. Materials and Methods: Lithium disilicate CAD‐milled abutments (n = 24) were cemented to titanium sleeve inserts and then screw attached to titanium fixtures. The assembly was then embedded at a 30° angle in polymethylmethacrylate. Each (n = 24) was restored with a resin‐cemented machined lithium disilicate all‐ceramic central incisor crown. Single load (lingual‐incisal contact) to failure was determined for three specimens. Fatigue testing (n = 21) was conducted employing the step‐stress method with lingual mouth motion loading. Failures were recorded, and reliability calculations were performed using proprietary software. Probability Weibull curves were calculated with 90% confidence bounds. Fracture modes were classified with a stereomicroscope, and representative samples imaged with scanning electron microscopy. Results: Fatigue results indicated that the limiting factor in the current design is the fatigue strength of the abutment screw, where screw fracture often leads to failure of the abutment metal sleeve and/or cracking in the implant fixture. Reliability for completion of a mission at 200 N load for 50K cycles was 0.38 (0.52% to 0.25 90% CI) and for 100K cycles was only 0.12 (0.26 to 0.05)—only 12% predicted to survive. These results are similar to those from previous studies on metal to metal abutment/fixture systems where screw failure is a limitation. No ceramic crown or ceramic abutment initiated fractures occurred, supporting the research hypothesis. The limiting factor in performance was the screw failure in the metal‐to‐metal connection between the prototyped abutment and the fixture, indicating that this configuration should function clinically with no abutment ceramic complications. Conclusion: The combined ceramic with titanium sleeve abutment prototype performance was limited by the fatigue degradation of the abutment screw. In fatigue, no ceramic crown or ceramic abutment components failed, supporting the research hypothesis with a reliability similar to that of all‐metal abutment fixture systems. A lithium disilcate abutment with a Ti alloy sleeve in combination with an all‐ceramic crown should be expected to function clinically in a satisfactory manner. [ABSTRACT FROM AUTHOR]

To evaluate the failure-load and survival-rate of screw-retained monolithic and bi-layered crowns bonded to titanium-bases before and after mouth-motion fatigue, 72 titanium-implants (SICvantage-max, SIC-invent-AG) were restored with three groups (n = 24) of screw-retained CAD/CAM implant-supported-single-crowns (ISSC) bonded to titanium-bases: porcelain-fused-to-metal (PFM-control), porcelain-fused-to-zirconia (PFZ-test) and monolithic LDS (LDS-test). Half of the specimens (n = 12/group) were subjected to fatigue in a chewing-simulator (1.2 million cycles, 198 N, 1.67 Hz, thermocycling 5–55 °C). All samples were exposed to single-load-to-failure without (PFM0, PFZ0, LDS0) or with fatigue (PFM1, PFZ1, LDS1). Comparisons were statistically analyzed with t-tests and regression-models and corrected for multiple-testing using the Student–Neuman–Keuls method. All PFM and LDS crowns survived fatigue exposure, whereas 16.7% of PFZ showed chipping failures. The mean failure-loads (±SD) were: PFM0: 2633 ± 389 N, PFM1: 2349 ± 578 N, PFZ0: 2152 ± 572 N, PFZ1: 1686 ± 691 N, LDS0: 2981 ± 798 N, LDS1: 2722 ± 497 N. Fatigue did not influence load to failure of any group. PFZ ISSC showed significantly lower failure-loads than monolithic-LDS regardless of artificial aging (p < 0.05). PFM ISSC showed significantly higher failure loads after fatigue than PFZ (p = 0.032). All ISSC failed in a range above physiological chewing forces. Premature chipping fractures might occur in PFZ ISSC. Monolithic-LDS ISSC showed high reliability as an all-ceramic material for screw-retained posterior hybrid-abutment-crowns. [ABSTRACT FROM AUTHOR]

Evaluate the effect of aging using two different methods on the three-dimensional fit of zirconia abutments at the implant-abutment connection and estimate the probability of survival of anterior crowns supported by straight and 17-degree angled abutments. Two different zirconia abutment designs, straight and 17-degree angled abutments (n = 63/group), were evaluated in the current study. The abutments were randomly allocated into three experimental groups according to laboratory aging condition (134°C, 2.2 bar, 20 h): (i) control, (ii) autoclave aging, and (iii) hydrothermal reactor aging. Crystalline content was determined by X-Ray diffraction (XRD) and Raman spectroscopy, and microstructure was analyzed using field-emission gun scanning electron microscope (FEG-SEM). Implant-abutment volume misfit was determined in the straight abutments by micro-computed tomography using the silicone replica technique. For fatigue testing, abutments were torqued to the implants and connected to standardized maxillary incisor zirconia crowns. The assemblies were subjected to step-stress accelerated life testing (SSALT) in water until fracture or suspension. The use level probability Weibull curves and probability of survival for a mission of 50,000 cycles at 50, 100, 150 and 200 N were calculated and plotted. Fractured samples were analyzed using a stereomicroscope and scanning electron microscope. The crystalline spectra depicted a zirconia system primarily composed of the tetragonal phase. Laboratory aging yielded a 20%- and 37%-increase in the monoclinic content for abutments aged in autoclave and hydrothermal reactor relative to control, respectively. A fully crystalline matrix with a regular grain size was observed in the FEG-SEM for control abutments, with a considerable presence of intergranular defects. While autoclave aging triggered no significant alteration to the microstructure, defect population was reduced after hydrothermal reactor aging. Control abutments presented a significantly higher volume misfit (2.128 ± 0.54 mm3) relative to aged abutments using autoclave (1.244 ± 0.48 mm3) or hydrothermal reactor (1.441 ± 0.41 mm3). The beta (β) values indicated that failures were predominantly controlled by material strength rather than fatigue damage accumulation for all groups, except for straight control abutments. Irrespective of aging, the probability of survival of straight and angled zirconia abutments was up to 95% (95–100%) at 50 and 100 N. A 50N-increase in the load resulted in wider range of survival estimate, with straight autoclave abutments percentage significantly lower probability of survival (77%) than angled hydrothermal reactor abutments (99%). At 200N, angled hydrothermal reactor (97%) or autoclave (82%) aged abutments demonstrated the highest probability of survival, angled control (71%) and straight hydrothermal reactor (69%) abutments intermediate values, and straight autoclave (23%) and control (7%) abutments the lowest estimate. The failure mode predominantly involved abutment and/or abutment screw fracture for both straight and angled abutments. Hydrothermal aging significantly influenced volume misfit, as well as the probability of survival of zirconia abutments at higher loads for both angled and straight abutments. [Display omitted] • Laboratory aging method influences degradation behavior of zirconia systems. • Aging triggered a significant increase in the monoclinic phase of zirconia abutments. • Aging significantly reduced volume misfit of zirconia abutments. • Aging can increase the probability of survival of zirconia abutments at high loads. [ABSTRACT FROM AUTHOR]

This study aimed to produce a new SiO 2 +Y-TZP ceramic via uniaxial/isostatic compression that was structurally and chemically characterized relating to its translucency and flexural strength. SiO 2 and Y-TZP were mixed using a ball mill, pressed and sintered at 1150 °C. The optical and mechanical properties of the specimens were compared to lithium disilicate (LD) and zirconia-reinforced lithium silicate (ZLS) (Kruskal-Wallis, α = 0.05). The Fourier Transform Infrared Spectroscopy bands suggested an interaction between Si, O and Zr. Contrast ratio and translucency parameter of the experimental ceramic were higher and lower, (p = 0.000001) respectively, than those of the LD and ZLS. The experimental ceramic presented similar flexural strength to ZLS, but lower than LD (p < 0.0001). It can be concluded that this processing method is efficient to obtain a SiO 2 +Y-TZP ceramic and 1150 °C crystallizes SiO 2 without inducing t-m transformation. The SiO 2 +Y-TZP ceramic presented lower translucency and higher masking ability than the commercially available glass-ceramics, but similar flexural strength to one glass-ceramics. Image 1 • Ceramics containing SiO 2 +Y-TZP can be produced via uniaxial/isostatic pressing. • The ball mill allows chemical interaction between SiO 2 and Y-TZP before sintering. • Sintering parameter crystallized SiO 2 without inducing t-m transformation of Y-TZP. • The lack of translucency could be caused by improper densification. • Reasonable flexural strength was achieved via uniaxial/isostatic pressing. [ABSTRACT FROM AUTHOR]

Dense and homogeneous nanostructured Y-TZP ceramics were prepared by colloidal processing and 2-step sintering using commercial powders. The influence of non-homogeneous yttria distributions on mechanical properties and Low-Temperature Degradation (LTD) resistance were assessed. Physical, structural, microstructural, and mechanical characterizations of all groups were evaluated and compared before and after artificial aging. Nanostructured Y-TZP samples with non-homogeneous yttria distributions presented the highest fracture toughness and elevated fracture strength. These samples were susceptible to LTD, but with the transformed monoclinic phase fraction restricted to the near-surface region. The characterization data of nanostructured samples were compared to those of conventional 3Y-TZP. The results of this work indicate that it may be possible to prepare Y-TZP ceramics with improved mechanical properties and resistance to LTD by careful and systematic design and engineering of nanostructures. [Display omitted] [ABSTRACT FROM AUTHOR]

Objective To compare the fatigue life and damage modes of zirconia crowns fabricated with and without framework design modification when porcelain veneered using a fast or slow cooling protocol. Methods Composite resin replicas of a first molar full crown preparation were fabricated. Zirconia copings were milled as conventional (0.5 mm even thickness, Zr-C, n = 20,) or modified (lingual margin of 1.0 mm thickness, 2.0 mm height connected to two proximal struts of 3.5 mm height, Zr-M, n = 20). These groups were subdivided ( n = 10 each) according to the veneer cooling protocol employed: fast cooling (Zr-CFast and Zr-MFast) and slow cooling (Zr-CSlow and Zr-MSlow). Crowns were cemented and fatigued for 10 6 cycles in water. The number of cycles to failure was recorded and used to determine the interval databased 2-parameter probability Weibull distribution parameter Beta ( β ) and characteristic life value Eta ( η ). Results 2-parameter Weibull calculation presented β = 5.53 and β = 4.38 for Zr-MFast and Zr-CFast, respectively. Slow cooled crowns did not fail by completion of 10 6 cycles, thereby Weibayes calculation was applied. Increased fatigue life was observed for slow cooled crowns compared to fast cooled ones. Groups Zr-MFast and Zr-MSlow presented no statistical difference. Porcelain cohesive fractures were mainly observed in fast cooled groups. Slow cooled crowns presented in some instances inner cone cracks not reaching the zirconia/veneer interface. Significance Improved fatigue life in tandem with the absence of porcelain fractures were observed in slow cooled crowns, regardless of framework design. Crowns fast cooled chiefly failed by porcelain cohesive fractures. [ABSTRACT FROM AUTHOR]

• Resin-matrix ceramics systems demonstrated high reliability at functional loads. • Resin-matrix ceramic fracture, chipping or catastrophic, is the chief failure mode. • Cracks originated by quasiplastic deformation under compression loading. To evaluate the fatigue survival, failure mode, and maximum principal stress (MP Stress) and strain (MP Strain) of resin-matrix ceramic systems used for implant-supported crowns. Identical molar crowns were milled using four resin-matrix ceramics (n = 21/material): (i) Shofu Hard, (ii) Cerasmart (iii) Enamic, and (iv) Shofu HC. Crowns were cemented on the abutments, and the assembly underwent step-stress accelerated-life testing. Use level probability Weibull curves at 300 N were plotted and the reliability at 300, 500 and 800 N was calculated for a mission of 50,000 cycles. Fractographic analysis was performed using stereomicroscope and scanning electron microscope. MP Stress and MP Strain were determined by finite element analysis. While fatigue dictated failures for Cerasmart (β > 1), material strength controlled Shofu Hard, Enamic, and Shofu HC failures (β < 1). Shofu HC presented lower reliability at 300 N (79%) and 500 N (59%) than other systems (>90%), statistically different at 500 N. Enamic (57%) exhibited a significant reduction in the probability of survival at 800 N, significantly lower than Shofu Hard and Cerasmart; however, higher than Shofu HC (12%). Shofu Hard and Cerasmart (>93%) demonstrated no significant difference for any calculated mission (300–800 N). Failure mode predominantly involved resin-matrix ceramic fracture originated from occlusal cracks, corroborating with the MP Stress and Strain location, propagating through the proximal and cervical margins. All resin-matrix ceramics crowns demonstrated high probability of survival in a physiological molar load, whereas Shofu Hard and Cerasmart outperformed Enamic and Shofu HC at higher loads. Material fracture comprised the main failure mode. [ABSTRACT FROM AUTHOR]

• High probability of survival was observed even for 0.5 mm restorations. • Models with thinner restorations accumulated more stress in the structures. • Resin-matrix ceramic materials seem up-and-coming systems for occlusal veneers. To evaluate the influence of resin-matrix ceramic material and thickness on reliability and stress distribution of occlusal veneers (OV). One hundred and twenty-six OV of a mandibular first molar were milled using a CAD/CAM system and allocated according to materials (resin nanoceramic (RNC) or polymer-infiltrated ceramic network (PICN)) and thicknesses (0.5, 1.0 and 1.5 mm), totaling six groups (RNC0.5, RNC1, RNC1.5, PICN0.5, PICN1, and PICN1.5). Step-stress accelerated-life testing was performed (n = 21/group) with the load applied at the distobuccal cusp tip of the occlusal veneer until failure or suspension. The use level probability Weibull curves and reliability were calculated and plotted (90% CI). Finite element analysis evaluated the stress distribution according to maximum principal stress (σ max) on the restoration and maximum shear stress (τ max) on the cement layer. There was no difference in the probability of survival for the estimated missions among the groups, except at 600 N in which the results were significantly lower to PICN1.5 (6%) compared to RNC1 (55%) and RNC1.5 (60%). The σ max values were higher for PICN (31.85–48.63 MPa) than RNC (30.78–33.09 MPa) in the same thicknesses. In addition, 0.5 mm groups concentrated more stress in the restoration (33.09–48.63 MPa) than 1.0 mm (31.11–35.36 MPa) and 1.5 mm (30.78–31.85 MPa) groups in the same material. Both resin-matrix ceramic materials seem up-and-coming restorative systems for occlusal veneers irrespective of the thicknesses as a consequence of the high reliability. [ABSTRACT FROM AUTHOR]