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Statement of Problem: New computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate glass-ceramics have been marketed. However, information concerning their biomechanical behavior is lacking., Purpose: The purpose of this in vitro study was to compare the fit and fatigue behavior of two recently introduced CAD-CAM lithium disilicate materials with the standard IPS e.max CAD ceramic and to investigate the effect of the thermal treatment for crystallization on crown fit., Material and Methods: Monolithic crowns (n=15) were milled from 3 CAD-CAM lithium disilicates: IPS e.max CAD (Ivoclar AG), Rosetta SM (Hass), and T-lithium (Shenzhen Upcera Dental Technology). Marginal and internal fit were evaluated using the replica technique before and after crystallization, and the fatigue behavior of the luted crowns was evaluated by the step-stress method. One-way ANOVA and the Tukey test were used to compare fit among the materials. Fatigue failure load was evaluated by the Kaplan-Meier and Mantel-Cox tests. The effect of crystallization on fit was evaluated with the paired t test (α=.05)., Results: Marginal fit was different between IPS e.max CAD (74 μm) and Rosetta SM (63 μm) (P=.02). T-lithium was similar to the other ceramics (68 μm) (P>.05). Occlusal internal space was similar among all materials (P=.69). Fatigue failure loads of Rosetta SM (1160 N) and T-lithium (1063 N) were similar to IPS e.max CAD (1082 N) (P>.05). The fatigue failure load of Rosetta SM was higher than that of T-lithium (P=.04). Crystallization reduced the axial internal space of all materials (P<.05) without significantly affecting marginal fit (P>.05)., Conclusions: The fit and fatigue behavior of Rosetta SM and T-lithium were similar to that of IPS e.max CAD. Crystallization reduced the internal space of the crowns., (Copyright © 2023 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

This study evaluated the effect of resin cement coating with high and low viscosities on the flexural fatigue strength of machined lithium disilicate glass-ceramic. Discs (IPS e.max CAD; Ivoclar Vivadent) were prepared and divided according to the surface condition (machining [M]-CEREC inLab; and polishing [P]-laboratory procedures), resin cement coating (with or without), and cement viscosity (high [H] and low [L]). The ceramic bonding surface was etched/primed by a one-step primer application followed by resin cement application (Variolink N base + high or low viscosity catalyst; Ivoclar Vivadent). Biaxial flexural fatigue strength was evaluated on a piston-on-three-ball set by the step-test method (n = 15) (initial stress: 60 MPa; incremental steps: 20 MPa; 10,000 cycles/step, at 20 Hz). Weibull statistics were used for fatigue data. Contact angle, topographic, and fractographic analysis were also performed. Machining produced statistically lower contact angle than polishing and a significant detrimental effect on the fatigue behavior (σ 0 M = 247.2 [246.9-268.3]; σ 0 P = 337.4 [297.8-382.4]). Machined groups followed by resin cement coating (σ 0 MH = 297.9 [276.0-321.5]; σ 0 Ml = 301.2 [277.1-327.4]) behaved similarly to the polished and coated groups (σ 0 PH = 342.0 [308.9-378.5]; σ 0 PL = 357.3 [324.7-393.1]), irrespective of the cement viscosity. Therefore, cement coating has able to revert the detrimental effects of the machining on the fatigue strength of lithium disilicate glass-ceramic. High and low viscosity cements behaved similarly in the improvement of CAD-CAM lithium disilicate fatigue strength., (© 2022 Wiley Periodicals LLC.)

Objective: To characterize the effect of pigmentation techniques on the fatigue behavior of a 4YSZ ceramic adhesively luted onto dentin analog (glass fiber-reinforced epoxy resin)., Methods: 4YSZ ceramic discs (Ø= 10 mm, 1 mm thickness) were allocated into 5 groups: Ctrl - unshaded (IPS e.max ZirCAD MT BL); Manuf - shaded by the manufacturer (IPS e.max ZirCAD MT A2); Brush - unshaded pigmented, pre-sintering, using a brush; Stain - unshaded pigmented, post-sintering, during glaze application; Brush+Stain - combination of both techniques. Color assessments ensured the same perceived color (Vita Classical A2). Dentin analog discs (Ø= 10 mm, 2.5 mm thickness) were obtained, paired with the 4YSZ discs, and adhesively luted using a resin cement. Cyclic fatigue testing (n = 15) was run (20 Hz; 10,000 cycles/step, initial load 200 N; step-size 100 N up to 700 N; then 50 N until specimen failure). Fractographic, roughness and topography analyses were performed., Results: No statistical (p > 0.05) detrimental influence were observed for fatigue outcomes (Ctrl = Manuf = Brush = Stain = Brush+Stain). However, the Brush+Stain technique induced inferior statistical (p < 0.05) fatigue performance compared to Stain. All failures were radial cracks with origin at the ceramic intaglio surface. The staining technique triggered statistically higher roughness (p < 0.05). Uniformly sized zirconia crystals were seen in the Ctrl, Manuf and Brush groups, and a smooth vitreous surface with encrusted pigments in the Stain and Brush+Stain groups., Significance: Pigmentation techniques (Vita Classical A2 shade) have no detrimental effect on the mechanical fatigue properties of 4YSZ ceramic adhesively luted onto dentin analog., (Copyright © 2022 Elsevier Inc. All rights reserved.)

It aims on evaluate the effect of the test environment on static fatigue behavior of lithium disilicate-based (LD), and yttrium oxide-stabilized zirconia (YSZ) ceramics. Specimens of LD (IPS e.max CAD, Ivoclar Vivadent) and YSZ (IPS e.max ZirCAD MO, 3 mol% Y2O3, Ivoclar Vivadent) were randomly allocated into three groups: tested in air, inert (paraffin oil, Sigma Aldrich) or distilled water. The static fatigue test (n=15) was performed using a piston-on-three ball assembly, adapted from ISO 6872, as follows: starting load 100 N for LD and 300 N for YSZ; loading application time set to 1 hour for each loading step; step size of 50 N for LD and 100 N for YSZ, applied successively until fracture. Data from static fatigue strength (MPa) and time to fracture (hours) were recorded. Fractographic analysis was executed. Survival analysis corroborates absence of influence of environment on static fatigue outcomes (fatigue strength, time to fracture and survival rates) for YSZ. For LD, specimens tested in air presented statistically superior survival rate and static fatigue strength (p= 0.025). In regards of time to fracture, LD tested in air were superior than when tested in distilled water (p=0.019) or inert (p=0.017) environments. No statistical differences for Weibull modulus were observed. Failures started on the tensile stress surface. Thus, the test environment did not affect slow crack growth (SCG) mechanisms during static fatigue test of YSZ ceramics, but it plays a significant role for the static fatigue behavior of lithium disilicate-based glass ceramics, indicating a high susceptibility to SCG.

This study aimed to evaluate the influence of loading frequency on the fatigue mechanical behavior of adhesively cemented polymer-infiltrated ceramic-network (PICN) and lithium disilicate (LD) simplified monolithic restorations. Thirty (30) disc-shaped specimens (Ø = 10 mm; thickness = 1.0 mm) of each ceramic material (PICN - Enamic, Vita Zahnfabrik or LD - IPS e.max CAD, Ivoclar Vivadent) were produced and adhesively cemented onto dentin analogue discs made of fiber and epoxy resin material (Ø = 10 mm; thickness = 2.0 mm). PICN and LD cemented assemblies were randomly allocated into 2 groups (n = 15) according to the loading frequency used for the fatigue testing (20 Hz or 2 Hz), composing the PICN&#95;20, PICN&#95;2, LD&#95;20 and LD&#95;2 testing groups. Fatigue tests were run using the step-stress approach (initial load = 200 N; step-size = 100 N; 10,000 cycles per step) and the collected data (fatigue failure load - FFL and number of cycles for failure - CFF) were analyzed by survival tests (Kaplan Meier and Mantel-Cox) and Weibull analysis. Fractographic analysis of failed specimens were also performed. No statistically significant differences were detected in relation to FFL and CFF between the groups within the same ceramic material (PICN&#95;20: 1127 N/102,667 cycles = PICN&#95;2: 1120 N/102,000 cycles; LD&#95;20: 980 N/88,000 cycles = LD&#95;2: 900 N/80,000 cycles). All failures were radial cracks in the cementation surface. Therefore, the use of a 20 Hz loading frequency shows to be a viable alternative to accelerate cyclic fatigue tests without affecting the fatigue mechanical behavior and the failure pattern of simplified restorations made of lithium disilicate glass ceramic or polymer infiltrated ceramic network bonded to the dentin analogue., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Considering the long time spent in low frequency cyclic fatigue tests, this study aimed to evaluate the influence of loading frequency (2 Hz and 20 Hz) on the flexural fatigue strength (FFS) and on the time and number of cycles to failure of a leucite-reinforced glass-ceramic. Disc-shaped specimens were produced using leucite-reinforced glass-ceramic CAD/CAM blocks (IPS Empress CAD), according to ISO 6872/2015. Two fatigue tests were performed. The FFS (n = 17) was determined by staircase approach at a lifetime of 500,000 cycles, for 2 Hz (control - chewing frequency estimative) and 20 Hz (accelerated approach). To determine the time and the number of cycles to failure in flexural fatigue, discs (n = 20) were submitted to a cyclic loading ranging from 10 MPa to 99 MPa (60% of the monotonic strength), until a maximum of 500,000 cycles. Means, standard deviation and confidence intervals (CI) at 95% for FFS were calculated, whereas statistical differences were detected based on maximum likelihood estimations and overlapping of 95% CIs. Kaplan Meier (α = 0.05) and log rank post-hoc tests were used to analyze the time (in minutes) and the number of cycles to failure in the lifetime test. FFS did not differ significantly between 2 Hz (mean: 78 MPa; 95% CI: 69-88 MPa) and 20 Hz (mean: 84 MPa; 95% CI: 78-90 MPa). Regarding the lifetime test, there was no difference (p = 0.3) in the time to failure for 2 Hz (mean: 13 min; 95% CI: 6-20 min) and 20 Hz (mean: 69 min; 95% CI: 9-128 min). However, the group tested with 20 Hz survived a significantly (p < 0.01) higher number of cycles (mean: 82,247 cycles; 95% CI: 11,450-153,044) than the group tested with 2 Hz (mean: 1588 cycles; 95% CI: 779-2397). Therefore, in leucite-reinforced glass-ceramic fatigue strength tests, limited to a lifetime of 500,000 cycles, the use of loading frequencies up to 20 Hz did not influence the FFS estimations when compared to 2 Hz (chewing frequency estimative), and may be an alternative to accelerate data collection in this type of mechanical test. However, in lifetime tests, the use of higher loading frequencies, as 20 Hz, did not save time, since a higher number of cycles was necessary to promote the failure, when compared to 2 Hz., Competing Interests: Declaration competing of interest No conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Objectives: To assess the effect of machining on the flexural fatigue strength and on the surface roughness of different computer-aided design, computer-aided manufacturing (CAD/CAM) ceramics by comparing machined and polished after machining specimens., Methods: Disc-shaped specimens of yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP), leucite-, and lithium disilicate-based glass ceramics were prepared by CAD/CAM machining, and divided into two groups: machining (M) and machining followed by polishing (MP). The surface roughness was measured and the flexural fatigue strength was evaluated by the step-test method (n=20). The initial load and the load increment for each ceramic material were based on a monotonic test (n=5). A maximum of 10,000 cycles was applied in each load step, at 1.4Hz. Weibull probability statistics was used for the analysis of the flexural fatigue strength, and Mann-Whitney test (α=5%) to compare roughness between the M and MP conditions., Results: Machining resulted in lower values of characteristic flexural fatigue strength than machining followed by polishing. The greatest reduction in flexural fatigue strength from MP to M was observed for Y-TZP (40%; M=536.48MPa; MP=894.50MPa), followed by lithium disilicate (33%; M=187.71MPa; MP=278.93MPa) and leucite (29%; M=72.61MPa; MP=102.55MPa). Significantly higher values of roughness (Ra) were observed for M compared to MP (leucite: M=1.59μm and MP=0.08μm; lithium disilicate: M=1.84μm and MP=0.13μm; Y-TZP: M=1.79μm and MP=0.18μm)., Significance: Machining negatively affected the flexural fatigue strength of CAD/CAM ceramics, indicating that machining of partially or fully sintered ceramics is deleterious to fatigue strength., (Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

This study evaluated the effects of different pre-sintering fabrication processing techniques of Y-TZP ceramic (CAD/CAM Vs. in-lab), considering surface characteristics and mechanical performance outcomes. Pre-sintered discs of Y-TZP ceramic (IPS e.max ZirCAD, Ivoclar Vivadent) were produced using different pre-sintering fabrication processing techniques: Machined- milling with a CAD/CAM system; Polished- fabrication using a cutting device followed by polishing (600 and 1200 SiC papers); Xfine- fabrication using a cutting machine followed by grinding with extra-fine diamond bur (grit size 30 μm); Fine- fabrication using a cutting machine followed by grinding with fine diamond bur (grit size 46 μm); SiC- fabrication using a cutting machine followed by grinding with 220 SiC paper. Afterwards, the discs were sintered and submitted to roughness (n=35), surface topography (n=2), phase transformation (n=2), biaxial flexural strength (n=20), and biaxial flexural fatigue strength (fatigue limit) (n=15) analyses. No monoclinic-phase content was observed in all processing techniques. It can be observed that obtaining a surface with similar characteristics to CAD/CAM milling is essential for the observation of similar mechanical performance. On this sense, grinding with fine diamond bur before sintering (Fine group) was the best mimic protocol in comparison to the CAD/CAM milling., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The aim of this study was to systematically review the literature to assess the effect of grinding on the mechanical properties, structural stability and superficial characteristics of Y-TZP ceramics. The MEDLINE via PubMed and Web of Science (ISI - Web of Knowledge) electronic databases were searched with included peer-reviewed publications in English language and with no publication year limit. From 342 potentially eligible studies, 73 were selected for full-text analysis, 30 were included in the systematic review with 20 considered in the meta-analysis. Two reviewers independently selected the studies, extracted the data, and assessed the risk of bias. Statistical analyses were performed using RevMan 5.1, with random effects model, at a significance level of 0.05. A descriptive analysis considering phase transformation, Y-TZP grain size, Vickers hardness, residual stress and aging of all included studies were executed. Four outcomes were considered in the meta-analyses (factor: grinding x as-sintered) in global and subgroups analyses (grinding tool, grit-size and cooling) for flexural strength and roughness (Ra) data. A significant difference (p<0.05) was observed in the global analysis for strength, favoring as-sintered; subgroup analyses revealed that different parameters lead to different effects on strength. In the global analysis for roughness, a significant difference (p<0.05) was observed between conditions, favoring grinding; subgroup analyses revealed that different parameters also lead to different effects on roughness. High heterogeneity was found in some comparisons. Generally grinding promotes decrease in strength and increase in roughness of Y-TZP ceramics. However, the use of a grinding tool that allows greater accuracy of the movement (i.e. contra angle hand-pieces coupled to slowspeed turbines), small grit size (<50μm) and the use of plenty coolant seem to be the main factors to decrease the defect introduction and allow the occurrence of the toughening transformation mechanism, decreasing the risk of deleterious impact on Y-TZP mechanical properties., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Purpose: To investigate the effects of a novel tribochemical silica coating technique with powders made from feldspathic ceramic and leucite-based ceramic on the bond strength of zirconia to resin cement before and after aging., Materials and Methods: Zirconia blocks were divided into 3 groups according to the material used for airborne-particle abrasion: 1) SP (control): silica-coated alumina particles; 2) FP: feldspathic ceramic powder; 3) LP: leucite glass-ceramic powder. After silanization, composite resin cylinders were cemented on the zirconia surface using a dual-curing resin cement. Prior to the shear bond strength (SBS) test, half of the samples (n = 15) were stored in distilled water for 24 h; the other half (n = 15) were submitted to aging (10,000 thermocycles of 5°C to 55°C; 150 days of water storage). The bond strength data were analyzed using two-way ANOVA and Tukey's test (α = 0.05). Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction analysis were performed., Results: The initial bond strengths did not differ significantly between the groups (p = 0.053). However, after aging procedures, airborne-particle abrasion with feldspathic ceramic powder (FP) resulted in higher values of bond strength (p = 0.0001). SEM and EDS indicated that all the treatments promoted silica deposition on the Y-TZP surface ceramic. Airborne-particle abrasion with FP and LP induced a lower percentage of the monoclinic phase., Conclusion: Airborne abrasion with fine feldspathic ceramic particles is a novel tribochemical technique and appears to be suitable for improving the bond strength between zirconia and resin cements.

Objective: To investigate the effect of firing protocols on flexural strength, surface roughness, and crystalline structure of a leucite-based glass ceramic., Methods: Discs produced by automated machining were distributed into five groups (n=30) according to the applied firing protocols, conducted above (790°C) or below (575°C) the ceramic transition temperature (Tg) (625±20°C): C - control, no heat treatment; G790 - glaze firing (790°C) for 1.5 min (manufacturer-recommended); G790-SC - G790 modified by slow cooling; EGF790-SC - extended G790 for 15 min, with slow cooling; and EF575-SC - extended firing below Tg at 575°C for 15 min, with slow cooling. Discs were subjected to biaxial flexural tests and results were assessed using Weibull analysis. Surface roughness was measured before and after treatments. One specimen from each group was used for X-ray diffraction (XRD)., Results: Highest values of characteristic strength (σ0) were obtained for EGF790-SC (211.7MPa). Regimens EF575-SC, G790-SC, and G790 produced σ0 values (167.9, 157.7, and 153.7MPa, respectively) lower than the control (C) (187.7MPa). The Weibull modulus (m) was statistically similar between groups. All treatments reduced the mean roughness (Ra) of the specimens. Extended cycles (EGF790-SC, EF575-SC) decreased the mean amplitude (Rz). XRD revealed no crystalline phase transformation and slight changes in size of leucite crystallites., Significance: Increased values of fracture strength and decreased surface roughness for a leucite-reinforced glass ceramic are achieved by extended glaze firing after machining. Crystalline structure is not modified. Glaze cycles, manufacturer-recommended or modified by slow cooling, and firing below Tg, significantly reduce fracture strength., (Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate the effects of hard machining, glaze firing and hydrofluoric acid etching on the biaxial flexural strength and roughness of a CAD/CAM leucite glass-ceramic; to investigate if ceramic post-machining surface roughness is influenced by the machining order and by the pair of burs used for it., Methods: A hundred forty four discs were machined by six nominally identical pairs of burs and divided into groups (n=24): (1) machining-M, (2) machining and glaze firing-MG, (3) machining and hydrofluoric acid etching-MA, (4) machining, glaze firing and hydrofluoric acid etching-MGA, (5) machining followed by polishing, as a control-MP, (6) machining, polishing and hydrofluoric acid etching-MPA. The roughness after each treatment (Ra and Rz) was measured. The discs were submitted to a piston-on-three ball flexure test (ISO 6872/2008) and strength data analyzed through Weibull statistics (95% CI)., Results: M resulted in lower characteristic strength (σ0) (128.2MPa) than MP (177.2MPa). The glaze firing reduced σ0 (109MPa), without affecting roughness. Hydrofluoric acid etching increased the roughness without affecting σ0. Spearman's coefficient (rs) indicated strong and significant correlation between machining order and roughness (rsRa=-0.66; rsRz=-0.73). The ceramic post-machining surface roughness differed significantly according to the pair of burs employed (p<0.05)., Significance: hard machining and glaze firing reduced the leucite ceramic strength, while hydrofluoric acid etching did not affect the strength. Variability in the roughness might be expected after machining, since it was influenced by the machining order and by the bur pairing., (Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)