Fatigue behavior, failure mode, and stress distribution of occlusal veneers: influence of the prosthetic preparation cusp inclinations and the type of restorative material.

OBJECTIVE: To evaluate the effects of cusp inclination of the prosthetic preparation's occlusal surface and type of restorative material on the fatigue behavior, failure mode, and stress distribution of occlusal veneers. MATERIALS AND METHODS: Glass fiber-reinforced epoxy resin prosthetic preparations for occlusal veneers with three different occlusal surface cusp inclination degrees (0°, 15°, and 30°) were produced and assigned into six testing groups (n = 11) according to the cusp inclination (0°, 15°, or 30°) and type of restorative material (lithium disilicate-LD or resin composite-RC). Despite different substrate preparation cusp inclination degrees, the restorations were designed maintaining 30° inclination between the cusps at the occlusal surface and a thickness of 0.7 mm at the central groove region of the restorations to be machined in a CAD/CAM system. After cementation, the specimens were stored for about 7 days (under water at 37 °C), and subsequently submitted to a load to failure test (n = 2) and an intermittent cyclic fatigue test (n = 9) (initial load: 100 N; step size: 50 N; cycles/step: 10,000; loading frequency: 20 Hz; loading piston: 6-mm-diameter stainless steel) until observing cracks. The data were analyzed by two-way ANOVA, Kaplan-Meier, and Mantel-Cox post hoc tests. Finite element analysis (FEA) and fractographic analyses were performed. RESULTS: The fatigue performance of LD and RC occlusal veneers was evaluated based on different prosthetic preparation cusp inclinations. The 0° inclination showed the best fatigue performance for both materials (LD: 944N, RC: 861N), while the 15° and 30° inclinations had lower values (LD: 800N and 533N, RC: 739N and 717N, respectively). The study also found that for a 0° inclination, LD occlusal veneers performed better than RC ones (LD: 944 N > RC: 861N), while for a 30° inclination, RC occlusal veneers had better fatigue performance than LD ones (LD: 533N < RC: 717N). No significant difference was observed between the materials for a 15° inclination (LD: 800N = RC: 739N). The FEA results showed a higher tensile stress concentration on lithium disilicate than on resin composite occlusal veneers. All lithium disilicate occlusal veneers showed radial crack failures, while resin composite occlusal veneers showed Hertzian cone cracks and radial cracks combined. CONCLUSION: Considering mechanical perspective only, RC occlusal veneers should be indicated when prosthetic preparation cusps inclinations are 30°. When 0° prosthetic preparation cusps inclinations are observed, LD occlusal veneers will behave mechanically better. When a 15° cusp inclination is preserved, both restorative materials behave similarly.

Effect of Hydrofluoric Acid Concentration on Resin Adhesion to a Feldspathic Ceramic.

PURPOSE: To evaluate the effect of different concentrations of hydrofluoric acid (HF) on the contact angle and the resin bond strength durability to feldspathic ceramic. MATERIALS AND METHODS: To evaluate the contact angles of distilled water on etched feldspathic ceramic, 25 specimens (12×10×2.4 mm) of VitaBlocks Mark II were used, divided into 5 groups (n=5): one unconditioned control (UC) group with no ceramic surface treatment, and 4 other groups that were etched for 60 s with different concentrations of HF: 1% (HF1), 3% (HF3), 5% (HF5) and 10% (HF10). The bond testing utilized 40 ceramic blocks (12×10×4 mm) that were fabricated and subjected to the same surface treatments as previously mentioned (excluding the control). The etched surfaces were silanized and resin cement was applied. After 24 h, the blocks were sectioned to produce bar specimens that were divided into two groups, non-aged (immediate testing) and aged (storage for 230 days+12,000 thermocycles at 5°C and 55°C), and subjected to microtensile testing (µTBS). Micromorphogical analysis of the treated surfaces was also performed (atomic force and scanning electron microscopy). One-way ANOVA and Tukey's tests were applied for data analysis. RESULTS: UC had the highest contact angle (61.4°), whereas HF10 showed the lowest contact angle (17.5°). In non-aged conditions, different acids promoted statistically similar bond strengths (14.2 to 15.7 MPa) (p>0.05); in terms of bond durability, only the bond strength of the HF1 group presented a statistically significant decrease comparing before and after aging (14.5 to 10.2 MPa). CONCLUSION: When etched with 3%, 5%, or 10% hydrofluoric acid, the ceramic tested showed stable resin adhesion after long-term aging.

How does the occlusal contact region influence the mechanical fatigue performance and fracture region of monolithic lithium disilicate ceramic crowns?

OBJECTIVE: To characterize the effect of the occlusal contact region on the mechanical fatigue performance and on the fracture region of monolithic lithium disilicate ceramic crowns. MATERIALS AND METHODS: Monolithic lithium disilicate ceramic crowns were machined in a CAD/CAM system and adhesively luted onto glass-fiber reinforced epoxy resin preparations with resin cement. The crowns were divided into three groups (n = 16) according to load application region (cusp tip: restricted to cusp tips; cusp plane: restricted to cuspal inclined plane; or mixed: associating tip cusp and cuspal inclined plane). The specimens were submitted to a cyclic fatigue test (initial load: 200 N; step-size: 100 N; cycles/step: 20,000; loading frequency: 20 Hz; load applicator: 6 mm or 40 mm diameter stainless steel) until observing cracks (1st outcome) and fracture (2nd outcome). The data were analyzed by the Kaplan-Meier + Mantel-Cox post-hoc tests for both outcomes (cracks and fracture). Finite element analysis (FEA), occlusal contact region, contact radii measurements, and fractographic analyzes were performed. RESULTS: The mixed group presented worse fatigue mechanical behavior (550 N / 85.000 cycles) compared to the cuspal inclined plane group (656 N / 111,250 cycles) (p < 0.05) for the first crack outcome, while the cusp tip group was similar to both groups (588 N / 97,500 cycles) (p > 0.05). The mixed group had the worst fatigue behavior (1413 N / 253,029 cycles) in relation to the other groups (Cusp tip: 1644 N / 293,312 cycles; Cuspal inclined plane: 1631 N / 295,174 cycles) considering the crown fracture outcome (p < 0.05). FEA showed higher tensile stress concentration areas just below the load application region. In addition, loading on the cuspal inclined plane induced a higher tensile stress concentration in the groove region. The most prevalent type of crown fracture was the wall fracture. Groove fracture was observed in 50% of the loading specimens exclusively on the cuspal inclined plane. CONCLUSION: Load application on distinct occlusal contact regions affects the stress distribution pattern and consequently the mechanical fatigue performance and fracture region of the monolithic lithium disilicate ceramic crowns. A combination of loading at distinct regions is recommended to promote better evaluation of the fatigue behavior of a restored set.

Effect of the region of the CAD/CAM block on the flexural strength and structural reliability of restorative materials.

The aim of the study was to evaluate whether the region (internal or external) of the CAD/CAM block influences the mechanical performance of restorative materials. Blocks of different CAD/CAM materials (Composites: KAV - Katana Avencia; LULT - LULT Ultimate; Ceramics: ENAM - Vita Enamic; NICE - N!CE; EMP - IPS Empress CAD; VMII - Vita Mark II; EMAX - IPS e.max CAD) were selected, and direct resin composite blocks (APX - Clearfil AP-X; FSUP - Filtek Supreme) were built using the incremental technique on a mold from one of the CAD/CAM blocks. All blocks were sectioned into bar-shaped specimens (1 × 1 × 14 mm), which were separated into two groups according to the region of the block (inside or outside). 3-point bending tests were performed following ISO 6872:2015 and flexural strength data were analyzed using one-way ANOVA and Bonferroni post-hoc tests (p < 0.05). Weibull module and characteristic strength were also calculated. In general, the mean flexural strength values were not statistically different (p > 0.05) between the inside and outside regions of each material, except for LULT (inside > outside) and EMAX (outside > inside). Comparing the materials, a similar strength (only discrete variations) was observed for inside, outside or merged (inside and outside data assembled together) regions: EMAX > KAV = LULT > NICE = APX > EMP = ENAM = VMII ≥ FSUP (merged condition). Characteristic strength at 63.2% failure probability and at 5% failure probability generally corroborates such observations. There were no statistical differences for Weibull module data (inside, outside, or merged), except for KAV and NICE (outside > inside). Thus, the region from where the restoration is milled within the CAD/CAM block generally does not influence the mechanical performance hereof (flexural strength, failure probability, risk of premature failures, and mechanical reliability) of the material, except for LULT and EMAX.

Ceramic surface conditioning, resin cement viscosity, and aging relationships affect the load-bearing capacity under fatigue of bonded glass-ceramics.

This study aimed to evaluate the influence of ceramic surface treatments, resin cement viscosities, and storage regimens on the fatigue performance of bonded glass-ceramics (lithium disilicate, LD; feldspathic, FEL). Ceramic discs (Ø = 10 mm; thickness = 1.5 mm) were allocated into eight groups per ceramic (n = 15), considering three factors: "ceramic surface treatment" in two levels - 5% hydrofluoric acid etching and silane-based coupling agent application (HF), or self-etching ceramic primer (E&P); "resin cement viscosity" in two levels - in high or low viscosity; and "storage regimen" in two levels - baseline, 24 h to 5 days; or aging, 180 days + 25,000 thermal cycles. Adhesive luting was performed onto glass fiber-reinforced epoxy resin discs (Ø = 10 mm; thickness = 2 mm) and the bonded assemblies were subjected to cyclic fatigue tests: initial load = 200 N; step-size = 25 N (FEL) and 50 N (LD); 10,000 cycles/step; 20 Hz. Scanning electron microscopy (SEM) inspections were performed. Regarding the LD ceramic, the fatigue behavior was reduced after aging for HF_HIGH and E&P_LOW conditions, while stable performance was observed for HF_LOW and E&P_HIGH. Regarding the FEL results, aging negatively affected HF_HIGH, E&P_HIGH, and E&P_LOW, being that only the HF_LOW condition presented a stable behavior. The failure initiated from defects on the etched surface of the ceramics, where the cross-sectional analysis commonly revealed unfilled areas. Long-term aging might induce a decrease in mechanical behavior. The 'ceramic microstructure/surface conditioning/resin cement viscosity relationships' modulate the fatigue performance of lithium disilicate and feldspathic glass-ceramics.

Cyclic fatigue tests on non-anatomic specimens of dental ceramic materials: A scoping review.

The aim of the present scoping review was to identify and discuss the methods, testing parameters, and characteristics used to induce cyclic fatigue on non-anatomic dental ceramic specimens. In vitro studies written in English which evaluated commercially-available non-anatomic dental ceramic specimens subjected to mechanical cyclic fatigue were selected. The search was performed in the PubMed, Scopus and Web of Science databases. The initial search yielded 1,636 articles, of which 81 were included. Based on the collected data, most of the included studies evaluated dental ceramic specimens cemented to supporting substrate (n= 42; 51.9%); used step-stress (n= 35; 42.2%) accelerated fatigue test, loading frequencies above 10 Hz (n= 31, 35.6%), stainless steel (n = 28, 32.6%) load applicator with spherical shaped tip 40 mm diameter (n= 25, 30.9%); applied only axial loads (n= 77, 95.1%); and considered a wet testing environment (n= 65, 78.3%). The definition of test geometry, method, and testing parameters must be cautiously considered according to the study objective and the scenario that is simulated. Accelerated fatigue tests, load frequencies up to 20 Hz, a 40 mm stainless steel spherical load applicator and a wet testing environment are the major common defined parameters presented in the existing literature. More studies exploring the influence of such factors on fatigue mechanism are necessary.

Do resin cement viscosity and ceramic surface etching influence the fatigue performance of bonded lithium disilicate glass-ceramic crowns?

OBJECTIVE: To assess the effects of a resin cement in high and low viscosity and distinct conditioning of the intaglio surface of lithium disilicate glass-ceramic crowns on fatigue performance of the crowns. METHODS: Prosthetic preparations (full-crown) in resin epoxy and crowns in lithium disilicate glass-ceramic were machined and allocated considering 2 factors (n = 10): "surface treatment" (HF - 5% hydrofluoric acid etching, followed by silane application; or E&P-self-etching ceramic primer) and "resin cement" (high or low viscosity). The preparations were etched with 10% hydrofluoric acid and an adhesive was applied. The intaglio surfaces of the ceramic crowns were treated as aforementioned (HF or E&P) and luted with high or low viscosity. The bonded sets were subjected to fatigue testing (step-stress approach: initial load of 200 N, step-size of 50 N, 10,000 cycles/step, 20 Hz) and complementary analyses (fractographic, topographic, and cross-sectional bonded interfacial zone analyses) were performed. RESULTS: Treatment with HF and silane with high viscosity resin cement (955 N/156,000 cycles) and E&P with low viscosity resin cement (1090 N/183,000 cycles) showed the best fatigue performance (statistical similarity between them). The failures originated from defects of the cement-ceramic interface, and the HF treatment induced a more pronounced topographical alteration. SIGNIFICANCE: Distinct topographical patterns from the HF and E&P treatments induced better fatigue results for the specific viscosity of the resin cement. Therefore, the fatigue performance depended on the existing topography, type of intaglio surface's defects/irregularities after surface treatment, and how the luting agent filled the irregularities.

Effects of material and piston diameter on the fatigue behavior, failure mode, and stress distribution of feldspathic ceramic simplified restorations.

This study evaluated the influence of the piston material (glass fiber-reinforced epoxy resin or stainless steel) and the piston tip diameter (6 or 40 mm) on the fatigue mechanical behavior, failure mode, and stress distribution of feldspathic ceramic simplified restorations. Pistons were machined in glass fiber-reinforced epoxy resin (ER) and in stainless steel (SS), with active tips simulating the curvature radius of 6- or 40-mm diameter spheres. A total of sixty (N= 60) feldspathic ceramic discs (Ø= 10 mm; thickness= 1.0 mm) were adhesively luted onto supporting substrate discs (Ø= 10 mm; thickness= 2.5 mm) and allocated into 4 groups (n= 15) according to the piston used for fatigue testing: ER_6, ER_40, SS_6, SS_40. Afterwards, the specimens were submitted to the cyclic fatigue test (20 Hz frequency; initial load= 100 N; step= 50 N; 10,000 cycles/step, upon specimen failure detection). The collected data were analyzed by two-way ANOVA (α= 0.05) to verify differences by considering 'piston material' and 'piston diameter' as factors, and their association. In addition, a survival analysis (Kaplan Meier with Mantel-Cox log-rank post-hoc tests) was conducted (α= 0.05). Fractographic and finite element (FEA) analyzes were also performed. 'Piston material' (p= 0.040, F= 4.43) and 'piston diameter' (p < 0.000, F= 563.21) had a significant influence on the fatigue failure load (FFL) and the number of cycles for failure (CFF) values. Feldspathic restorations showed higher FFL and CFF (p < 0.05) when tested with a 40 mm diameter piston compared to a 6 mm diameter piston (ER_40 and SS_40 > ER_6 > SS_6). In relation to the piston material, ER and SS pistons with 40 mm diameter promoted similar fatigue performance (ER_40: 946.67 N/179,333 cycles = SS_40: 936.67 N/177,333 cycles), while 6 mm diameter groups presented different fatigue performance (ER_6: 440 N; 78,000 cycles > SS_6: 353.3 N; 60,667 cycles). Hertzian cone crack failures were only observed in the groups tested with 6 mm pistons, regardless of piston material. Higher stress concentration on the ceramic surface was observed when using 6 mm diameter pistons, whereas the SS_6 group showed a slight increase in stress concentration in comparison to the ER_6 group. The piston diameter showed an influence on the fatigue behavior, failure mode, and stress distribution of feldspathic ceramic simplified restorations. However, the influence of piston material is only observed when 6 mm diameter pistons are used. The 40 mm diameter pistons led to radial crack, being more appropriate for fatigue test of simplified feldspathic ceramic restorations with a thickness ≤ 1 mm. Whilst the 6 mm diameter pistons should be avoided, once tend to induce Hertzian cone crack failures and to underestimate fatigue performance.

Alumina particle air-abrasion and aging effects: Fatigue behavior of CAD/CAM resin composite crowns and flexural strength evaluations.

The aim of this study was to characterize the flexural strength and elastic modulus of CAD/CAM resin composite material and to evaluate the influence of different surface treatments and storage conditions on the fatigue behavior of bonded composite crowns. Bars (flexural strength, n= 30; elastic modulus, n= 5) (1.2 × 4 × 12 mm) were produced for three-point bending test and CAD/CAM milled crowns (n= 5) (thickness= 1 mm) adhesively cemented to an epoxy resin substrate for fatigue tests. Bars and crowns were randomly allocated into two "surface treatments": no surface treatment (CTRL) and air-abrasion with 110 µm Al2O3 particles (AlOx); while the crowns were also subdivided into "aging condition" (baseline - storage for 24 h to 7 days, and aging - storage for 150 days + 25,000 thermal cycles). The three-point bending test was performed according to ISO 6872 and the luted crowns were subjected to step-stress fatigue test (initial load of 200 N; step-size of 50 N; 10,000 cycles per step; 20 Hz). Complementary analysis by Stereomicroscopy and Field Emission Scanning Electron Microscopy (FE-SEM) were performed. The flexural strength and fatigue data were submitted to statistical tests (α= 0.05). The results showed that air-abrasion reduces the flexural strength and the characteristic strength of the resin composite, without modifying its elastic modulus or its structural reliability (Weibull Modulus). Air-abrasion did not influence the fatigue behavior of the cemented crowns. Notwithstanding, a decrease in the survival rate was observed after 445,000 cycles (2,400 N) when subjected to aging at both the CTRL or AlOx conditions. FE-SEM micrographs of the crowns showed that alumina particle air-abrasion treatment can modify the topography of its treated inner surface. Therefore, air-abrasion with alumina powder introduces defects onto the surface of the CAD/CAM resin composite material, decreasing the flexural strength, but without changing its elastic modulus and reliability. Adhesive cementation onto an epoxy resin substrate prevented an influence of the introduced defects on the fatigue performance of the resin composite restoration. Nevertheless, the fatigue behavior may be damaged by aging regimen.

Influence of the foundation substrate on the fatigue behavior of bonded glass, zirconia polycrystals, and polymer infiltrated ceramic simplified CAD-CAM restorations.

This study evaluated the influence of distinct substrates on the mechanical fatigue behavior of adhesively cemented simplified restorations made of glass, polycrystalline or polymer infiltrated-ceramics. CAD/CAM ceramic blocks (feldspathic - FEL; lithium disilicate - LD; yttria-stabilized zirconia - YZ; and polymer-infiltrated ceramic network - PICN) were shaped into discs (n = 15, Ø = 10 mm; thickness = 1.0 mm), mimicking a simplified monolithic restoration. After, they were adhesively cemented onto different foundation substrates (epoxy resin - ER; or Ni-Cr metal alloy - MA) of the same shape (Ø = 10 mm; thickness = 2.0 mm). The assemblies were subjected to fatigue testing using a step-stress approach (200N-2800 N; step-size of 200 N; 10,000 cycles per step; 20 Hz) upon the occurrence of a radial crack or fracture. The data was submitted to two-way ANOVA (α = 0.05) to analyze differences considering 'ceramic material' and 'type of substrate' as factors. In addition, a survival analysis (Kaplan Meier with Mantel-Cox log-rank post-hoc tests; α = 0.05) was conducted to obtain the survival probability during the steps in the fatigue test. Fractographic and finite element (FEA) analyzes were also conducted. The factors 'ceramic material', 'type of substrate' and the interaction between both were verified to be statistically significant (p < .001). All evaluated ceramics presented higher fatigue failure load (FFL), cycles for failure (CFF) and survival probabilities when cemented to the metallic alloy substrate. Among the restorative materials, YZ and LD restorations presented the best fatigue behavior when adhesively cemented onto the metallic alloy substrate, while FEL obtained the lowest FFL and CFF for both substrates. The LD, PICN and YZ restorations showed similar fatigue performance considering the epoxy resin substrate. A more rigid foundation substrate improves the fatigue performance of adhesively cemented glass, polycrystalline and polymer infiltrated-ceramic simplified restorations.

Step-stress vs. staircase fatigue tests to evaluate the effect of intaglio adjustment on the fatigue behavior of simplified lithium disilicate glass-ceramic restorations.

The aim of the study was to compare the outcomes for the fatigue mechanical behavior of bonded simplified lithium disilicate restorations, with and without an internal adjustment by grinding with diamond bur in running two fatigue tests: Staircase and Step-stress testing approaches. Ceramic discs (IPS e.max CAD) were prepared (Ø = 10 mm; thickness = 1.0 mm), submitted to an in-lab simulation of CAD/CAM milling (#60 SiC paper) and allocated into 2 groups according to the internal adjustment by grinding of the cementation surface: no adjustment (CTRL); or grinding with a coarse diamond bur (GR). Adhesive cementation (Multilink N) was performed onto epoxy resin discs (Ø = 10 mm; thickness = 2 mm) after ceramic/epoxy surface treatments. The cemented assemblies of each group were randomly assigned into 2 subgroups considering two fatigue tests (n = 15): Staircase - SC (250,000 cycles; 20 Hz), or Step-stress - SS (10,000 cycles per step; 20 Hz). Roughness, topographic and fractographic analyses were additionally performed. Statistical analyses were carried out using the Dixon and Mood method for Staircase data, and Kaplan-Meier and Mantel-Cox (log-rank) tests for Step-stress data. Ceramic restorations having its intaglio surface ground (GR group: SC test = 306.67 N; SS test = 646.67 N) presented lower fatigue failure load (FFL) values than the CTRL group (SC test = 879.28 N; SS test = 1090.00 N), regardless of the fatigue testing approach. The percentage of mean FFL decrease comparing the CTRL to GR group was higher for SC (65.1%) than the SS (40.7%) approach. However, a different total number of cycles was applied for each method. Both fatigue tests were able to detect the negative effect of internal adjustments of lithium disilicate glass-ceramic simplified restorations on their mechanical behavior. Therefore, both methods can be applied for similar evaluations (fatigue testing for ceramic restorations).

Different Etching Times of a One-step Ceramic Primer: Effect on the Resin Bond Strength Durability to a CAD/CAM Lithium-Disilicate Glass-Ceramic.

PURPOSE: To evaluate the effect of different etching times of a self-etching ceramic primer on the microshear bond strength (µSBS) and topographic surface pattern of a lithium-disilicate glass-ceramic. MATERIALS AND METHODS: Ceramic slices were subjected to an in-lab simulation of CAD/CAM milling and randomly allocated to 10 groups (n = 35) considering two factors: "surface treatment" in 5 levels - one control group (5% hydrofluoric acid + silane application [HF5+SIL]), and 4 experimental groups using ceramic etching/primer (Monobond Etch & Prime, E&P) with different passive application times (40 s, 2 min, 5 min, or 10 min); and "aging" factor in 2 levels - short-term (after 24 h), or long-term (storage for 180 days + 12,000 thermal cycles). Composite cement cylinders were built and µSBS tests were run in a universal testing machine. The failure patterns were categorized, and complementary analyses with SEM and Atomic Force Microscopy (AFM) were performed. RESULTS: The groups showed statistically similar bond strengths in the short term (range 22.4 to 25.1 MPa). However, only the E&P 20s+40s (19.3 MPa) and E&P 20s+5min (21.5 MPa) groups maintained stable bond strength in the long term, and HF5+SIL (17.1 MPa) presented statistically significantly lower values than did E&P 20s+5min. The failure pattern was predominantly adhesive. The increased application time of the ceramic primer promoted greater dissolution of the glass matrix; thus, the E&P 20s+10min group presented the most complex surface characteristics in the fractal dimension analysis. CONCLUSION: The self-etching ceramic primer can be used as an alternative to classical conditioning with HF plus silane, promoting stable bond strength for etching times of 40 s or 5 min of passive application.

Accelerated loading frequency does not influence the fatigue behavior of polymer infiltrated ceramic network or lithium disilicate glass-ceramic restorations.

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_20, PICN_2, LD_20 and LD_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_20: 1127 N/102,667 cycles = PICN_2: 1120 N/102,000 cycles; LD_20: 980 N/88,000 cycles = LD_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.

Effect of resin cement space on the fatigue behavior of bonded CAD/CAM leucite ceramic crowns.

This study evaluated the influence of occlusal resin cement space on the fatigue performance of bonded-leucite crowns to a dentin-analogue material. Leucite anatomical crowns were adhesively cemented to dentin-like preparations having distinct occlusal cement space (50, 100 and 300 µm) (n = 18), and subjected to step-stress fatigue testing (150 N - 350 N; step-size: 25 N; 20,000 cycles/step; 20 Hz). Fatigue data (load and number of cycles for failure) were analyzed using Kaplan-Meier and Mantel-Cox (log-rank) tests (p <0.05). Fractographic analysis and occlusal internal space measurements were also performed. There was no significant difference for the distinct occlusal cement layer (50 µm: 289 N, 136,111 cycles; 100 µm: 285 N, 132,778 cycles; 300 µm: 246 N, 101,667 cycles). Occlusal internal space analysis showed a mean thickness of 120.4 (50 µm), 174.9 (100 µm) and 337.2 (300 µm). All failures were radial cracks originating at the ceramic-cement interface. Distinct occlusal cement spaces had no effect on the fatigue behavior of anatomical leucite crowns.

One-step ceramic primer as surface conditioner: Effect on the load-bearing capacity under fatigue of bonded lithium disilicate ceramic simplified restorations.

The aim of the study was to evaluate the effect of a ceramic primer and its increased passive application on the fatigue performance of adhesively cemented lithium disilicate simplified restorations. Ceramic discs (Ø = 10 mm; thickness = 1.0 mm) were submitted to an in-lab simulation of CAD/CAM milling and allocated into 8 groups (n = 15), considering 2 factors: "surface treatment"- PRIMER, only coupling agent application (Monobond N); HF5+PRIMER, 5% hydrofluoric acid and coupling agent; E&P 20s + 40s and E&P 20s+5min, ceramic etching/priming (Monobond Etch & Prime, E&P) for 20 s of active application followed by 40 s or 5 min of passive application, respectively; and "aging condition"- baseline, storage for 24 h to 5 days; aged, storage for 90 days +12,000 thermal cycles. Adhesive cementation (Multilink N) was performed onto epoxy discs (Ø = 10 mm; thickness = 2 mm) and the cemented assemblies were subjected to step-stress fatigue tests (initial load of 200 N; step-size of 50 N; 10,000 cycles per step; 20 Hz). The results showed that the groups had similar fatigue performance in the baseline condition (except for E&P 20s+5min: 940.0 N; 123,000 cycles > PRIMER: 786.7 N; 92,333 cycles). When aged, the PRIMER group presented the worst fatigue performance (480.8 N; 31,154 cycles) compared to the other groups (810.0-840.0 N; 97,000-103,000 cycles). In addition, only the PRIMER treatment showed unstable fatigue performance (baseline > aged). Therefore, ceramic surface treatment promoting micromechanical interlocking and chemical bonds is mandatory for stable fatigue performance of adhesively cemented lithium disilicate restorations. The one-step ceramic primer/conditioner promoted similar fatigue performance to the 5% hydrofluoric acid + coupling agent, but increased E&P etching time did not improve the fatigue behavior.

Survival probability of zirconia-reinforced lithium silicate ceramic: Effect of surface condition and fatigue test load profile.

OBJECTIVES: The present investigation evaluated the step stress accelerated test (SSALT) load profiles on the survival probability of a glass ceramic under two surface conditions (polished or roughened). METHODS: Suprinity-ZLS blocks (Vita Zhanfabrik) were shaped into cylinders, cut in a sawing machine, and crystalized according to the manufacturer's instructions. 60 discs were obtained (Ø=12mm, thickness=1.2mm) and randomly assigned into two surface conditions: "p" polished surface (400-1200-grit SiC papers), and "r" roughened surface (200-grit SiC papers). Profilometry was performed in all discs to evaluate average surface roughness prior to flexural fatigue strength testing. 3 discs of each group were submitted to biaxial flexural strength in an universal testing machine (0.5mm/min) and the mean load to failure (N) was calculated to determine SSALT profiles. 27 specimens per surface condition were assigned into three profiles - Mild (n=9), Moderate (n=9), and Aggressive (n=9), and submitted to the fatigue test (60-320N, 140,000 cycles at 1.4Hz). The results were analyzed using the Kaplan-Meier and Wilcoxon tests (5%), 2-way ANOVA and Tukey test (α=5%). RESULTS: Kaplan-Meier and generalized Wilcoxon showed (P=0.002) that polished groups showed higher survival probability than roughened condition (P<0.05). A rough internal surface impacted deleteriously on the fatigue strength and reliability of ZLS ceramic. Both surface conditions were more sensitive to the aggressive profile than the other profiles, even worst for the roughened group. Regardless the load profile, 0% survival probability was observed at 384MPa for polished condition. While for roughened, aggressive tested specimens did not survived 147MPa followed by moderate at 312MPa and mild at 384MPa. The failure modes showed fracture marks originating from superficial grooves for both surface conditions. SIGNIFICANCE: Polished specimens are sensitive to the load profile variation, confirming the effect of surface morphology on the fatigue results.

Load-bearing capacity under fatigue and survival rates of adhesively cemented yttrium-stabilized zirconia polycrystal monolithic simplified restorations.

This study evaluated the fatigue failure load, number of cycles for failure and survival probability of 2nd and 3rd generation yttrium-stabilized zirconia (YSZ) adhesively cemented to a dentin analogue substrate. Disc-shaped specimens (n = 10; Ø = 10 mm; thickness = 1.0 mm) were produced from four 2nd generation YSZs (Lava Plus, 3M ESPE; Vita In-Ceram YZ-HT, VITA Zahnfabrik; Zirlux FC, Ivoclar Vivadent; Katana ML-HT, Kuraray) and two 3rd generation YSZs (Katana UTML and Katana STML, Kuraray). Each YSZ disc was adhesively cemented (Multilink Automix System) onto its dentin analogue pair (epoxy resin, Ø = 10 mm; thickness = 2.5 mm). Fatigue tests were conducted through step-stress approach (load ranging from 400 to 2600 N; step-size of 200 N; 20,000 cycles per step, 20 Hz) and the obtained data were analyzed using Kaplan Meier and Mantel-Cox tests. Surface topography and phase transformation (m-, t-, and c-phases) inspections after particle air-abrasion of the YSZs were performed, as well as fractographic analysis of the failed specimens. Second-generation zirconia materials presented higher fatigue failure load, number of cycles for failure, and survival probability than 3rd generation. Similar topographical characteristics of the YSZs could be noted. Phase transformation (t- to m-phase) after YSZ air-abrasion was only observed for 2nd generation materials. All failures started from the surface/sub-surface defects located at the cementation interface. 2nd generation zirconia presented higher load-bearing capacity under cyclic loading than 3rd generation materials.

Fatigue Failure Load of Resin-bonded Simplified Lithium Disilicate Glass-Ceramic Restorations: Effect of Ceramic Conditioning Methods.

PURPOSE: To evaluate the influence of different ceramic surface conditioning methods on the fatigue failure load of adhesively cemented simplified lithium-disilicate glass-ceramic restorations. MATERIALS AND METHODS: Ceramic (IPS e.max CAD, Ivoclar Vivadent) (Ø = 10 mm; thickness = 1.2 mm) and epoxy resin (Ø = 10 mm; thickness = 2.3 mm) disks were produced. The ceramic bonding surfaces were treated as follows: no etching and MPS-silane primer application only (MN); etching with 10% hydrofluoric acid (HF) for 20 s followed by primer application (HF + MN); HF + universal multimode adhesive application (HF + SU); etching with a one-step etching primer (ME&P); HF + primer + conventional adhesive (HF + MN + PAB). The epoxy resin disks were etched with 10% HF for 20 s followed by a coat of bonding agent (Multilink Primer A+B). Pairs of ceramic/epoxy resin disks were cemented with composite cement (Multilink N, Ivoclar Vivadent). The mean fatigue failure load was determined by the staircase method (100,000 cycles at 20 Hz frequency; initial load = 1435 N; step size = 72 N). RESULTS: ME&P had the highest fatigue failure load, followed by HF etched groups, while the non-etched condition (MN group) had the lowest. All samples presented radial cracks originating from defects at the conditioned ceramic surface (interface). CONCLUSION: The simultaneous physicochemical conditioning with one-step self-etching ceramic primer promoted the best fatigue behavior results of the glass-ceramic restorations. It might indicate that this one-step conditioning reduces the number of flaws at the ceramic surface due to the slighter surface alterations than those produced by hydrofluoric acid etching, improving the fatigue behavior.

CAD-CAM milled versus pressed lithium-disilicate monolithic crowns adhesively cemented after distinct surface treatments: Fatigue performance and ceramic surface characteristics.

To evaluate the fatigue failure load (FFL), number of cycles for failure (CFF) and survival probabilities of lithium-disilicate (LD) monolithic crowns manufactured by two processing techniques (pressing vs. CAD/CAM) adhesively cemented to a dentin-analogue material, considering two surface treatments (conventional vs. simplified). Surface characteristics (topography, roughness and fractal dimensions) were also assessed. Forty (40) monolithic crowns were manufactured considering two specific processing techniques for each ceramic system: LDCAD - CAD/CAM lithium-disilicate (IPS e.max CAD, Ivoclar Vivadent); LDPRESS - pressed lithium-disilicate (IPS e.max Press, Ivoclar Vivadent). The crowns were adhesively cemented (Multilink Automix System, Ivoclar Vivadent) onto dentin analogue preparations considering two distinct protocols of surface treatments (conventional - hydrofluoric acid etching + silane application [HF+Sil] or simplified - etching with one-step primer (Monobond Etch&Prime, Ivoclar Vivadent) [EP]). The cemented assembly was stored in distilled water at 37 °C for 3 days and fatigue tests were run (step-stress approach: load ranging from 400 to 2000 N, step-size of 100 N, 15,000 cycles/step, 20 Hz). Fractography, surface topography, roughness, and fractal dimension analyses were performed. LDPRESS[EP] group depicted higher FFL, CFF and survival probabilities in comparison to LDCAD groups, regardless of the conditioning method. A tendency of higher Weibull modulus (mechanical reliability) was observed when using [EP] for both LDPRESS and LDCAD. SEM and AFM analysis showed very distinct initial surface patterns for the distinct processing techniques considered (LDCAD with higher fractal dimension and lower roughness than LDPRESS), and both surface treatments distinctly affected these surface characteristics. All failures were radial cracks originating at the ceramic-cement interface. Pressed lithium-disilicate monolithic crowns showed better fatigue performance in comparison to CAD/CAM milled crowns, especially when they were treated with self-etching ceramic primer. The surface treatment with self-etching primer led to similar fatigue performance when compared to hydrofluoric acid plus silane application for the same processing technique, but it tended to provide higher mechanical reliability.

Newer vs. older CAD/CAM burs: Influence of bur experience on the fatigue behavior of adhesively cemented simplified lithium-disilicate glass-ceramic restorations.

This study evaluated the effect of the CAD/CAM burs experience (newer vs older as consequence of the milling sequence) on fatigue failure load (FFL), number of cycles for failure (CFF), and survival rates of lithium disilicate glass-ceramic simplified restorations adhesively cemented to a dentin analogue substrate. Three sets of CAD/CAM burs were used to mill disc-shaped ceramic specimens (1 bur set - 18 milled discs with 10 mm diameter and 1.5 mm thickness), considering the bur experience as a result of the milling sequence to compose the study groups: G1-6 - discs obtained from the 1st to 6th milling of each bur set; G7-12 - specimens from the 7th to 12th milling; G13-18 - discs from the 13th to 18th. Discs of dentin analogue (G10, 10 mm diameter and 2.0 mm thickness) were made to serve as substrate (base material) and randomly assigned into pairs with the respective ceramic discs. Then, the ceramic discs were adhesively cemented onto the dentin analogue substrate, composing a three-layer specimen that mimics a monolithic restoration of a posterior tooth. Specimens were tested under stepwise fatigue approach: frequency = 20 Hz, 5000 cycles at maximum load of 400 N to accommodate the testing assembly, followed by incremental steps of 200 N with initial load ranging from 10 to 1000 N, to a maximum of 20,000 cycles/each step, until the occurrence of failure (radial crack). FFL and CFF were recorded at the end of the testing and subjected to statistical analysis. Supplementary roughness analysis of the milled surface was performed (n = 18) using a contact profilometer. Residual stress after milling and acid etching were accessed via X-ray Diffractometry analysis. FFL and CFF were not affected by increase on bur experience (no statistical differences among groups), despite that, it affected both Ra and Rz parameters (G1-6 had the smoothest surface). The residual stress concentration was negligible (milling did not induce residual stress concentration). It is concluded that the fatigue behavior of adhesively cemented lithium-disilicate glass-ceramic restorations was not influenced by CAD/CAM bur experience (newer vs older as consequence of the milling sequence), and so the residual stress concentration induced by milling was negligible.