Effect of different surface treatments on optical, colorimetric, and surface characteristics of a lithium disilicate glass-ceramic.

OBJECTIVE: To evaluate the effect of surface treatments on optical, colorimetric, and surface characteristics of lithium disilicate glass-ceramic. MATERIALS AND METHODS: Specimens (n = 5, IPS e.max CAD) were randomly allocated to the following treatments: mirror-polished: SiC papers; as-cut: mimicking CAD-CAM milling; ground: 90-120 µm-grit diamond bur; ground polished: ground, finished (46-30 µm-grit diamond bur), polished (diamond cups, brush and diamond paste); ground glazed: ground, glazed; ground polished glazed: association of methods. CIELAB color coordinates were obtained by a spectrophotometer. CIEDE2000 color differences (ΔE00 ) and the translucency parameter (TP00 ) were calculated. Light transmittance was assessed with a colorimeter. Surface characteristics (topography and roughness) were analyzed. Statistical differences for each condition and outcome were detected using one-way ANOVA with Tukey's post-hoc test (α = 0.05). RESULTS: TP00 data show statistical reduction after grinding (p < 0.05), which was only restored with polishing (solely or with glazing). ΔE00 shows that grinding results in perceptible variations in color (above 0.81), which were restored after all post-processing protocols (exception to only glaze application in contact with a black background). Light transmittance data corroborated such performance. Polishing and glazing reduced roughness and improved surface topography. CONCLUSION: Grinding statistically increased roughness, reduced translucency, light transmittance through the ceramic, and resulted on color differences. On contrary, polishing (followed or not by glazing) reduced roughness and enhanced ceramic translucency and light transmittance. Glaze also reduced roughness, but it still presented reduced translucency. The positioning (facing up or down) of the ceramic treated surface influenced the considered outcomes. CLINICAL SIGNIFICANCE: Grinding with diamond burs results in a deleterious impact to the optical, colorimetric and surface characteristics of lithium disilicate ceramic. Thus, polishing (followed or not by glazing) is recommended for optical and topographical enhancements when lithium disilicate monolithic restorations require occlusal adjustments.

Fatigue performance of adhesively luted glass or polycrystalline CAD-CAM monolithic crowns.

STATEMENT OF PROBLEM: Data comparing the fatigue performance of adhesively luted glass or polycrystalline ceramic systems for computer-aided design and computer-aided manufacturing (CAD-CAM) are scarce. PURPOSE: The purpose of this in vitro study was to evaluate and compare the fatigue performance of monolithic crowns manufactured from glass or polycrystalline CAD-CAM ceramic systems adhesively luted to a dentin analog. MATERIALS AND METHODS: Fifty-four pairs of standardized preparations of dentin analog (NEMA Grade G10) and simplified ceramic crowns of 1.5-mm thickness were obtained with 3 ceramic materials: lithium disilicate (LD) glass-ceramic (IPS e.max CAD); zirconia-reinforced lithium silicate (ZLS) glass-ceramic (Vita Suprinity); and translucent yttrium fully stabilized polycrystalline zirconia (Trans YZ) (Prettau Anterior). The simplified crowns (n=15) were adhesively cemented onto the preparations and subjected to step-stress fatigue test (initial load of 400 N, 20 Hz, 10 000 cycles, followed by 100-N increment steps until failure). Collected data (fatigue failure load [FFL] and cycles for failure [CFF]) were submitted to survival analysis with the Kaplan-Meier and Mantel-Cox post hoc tests (α=.05) and to Weibull analysis (Weibull modulus and its respective 95% confidence interval). Failed crowns were submitted to fractography analysis. The surface characteristics of the internal surface (roughness, fractal dimension) of additional crowns were accessed, and the occlusal cement thickness obtained in each luted system was measured. RESULTS: Trans YZ crowns presented the highest values of FFL, CFF, and survival rates, followed by ZLS and LD (mean FFL: 1740 N>1187 N>987 N; mean CFF: 149 000>92 613>73 667). Weibull modulus and cement thickness were similar for all tested materials. LD presented the roughest internal surface, followed by ZLS (mean Ra: 226 nm>169 nm>93 nm). The LD and ZLS internal surfaces also showed higher fractal dimension, pointing to a more complex surface topography (mean fractal dimension: 2.242=2.238>2.147). CONCLUSIONS: CAD-CAM monolithic crowns of Trans YZ show the best fatigue performance. In addition, ZLS crowns also showed better performance than LD crowns.

Ceramic Surface Treatment with a Single-component Primer: Resin Adhesion to Glass Ceramics.

PURPOSE: To evaluate the microshear bond strength (µSBS) of composite cement bonded to two machined glass ceramics and its durability, comparing conventional surface conditioning (hydrofluoric acid + silane) to a one-step primer (Monobond Etch & Prime). MATERIALS AND METHODS: Machined slices of lithium disilicate ceramic (LDC) (IPS e.max CAD) and feldspathic ceramic (FC) (VITA Mark II) glass ceramics were divided into two groups (n = 10) according to two factors: 1. surface treatment: HF+S (ca 5% hydrofluoric acid [IPS Ceramic Etching GEL] + silane coupling agent [SIL; Monobond Plus]) or MEP (single-component ceramic conditioner; Monobond Etch & Prime); 2. storage condition: baseline (without aging; tested 24 h after cementing) or aged (70 days of water storage + 12,000 thermal cycles). Composite cement (Multilink Automix, Ivoclar Vivadent) was applied to starch matrices on the treated ceramic surfaces and photoactivated. A µSBS test was performed (0.5 mm/min) and the failure pattern was determined. Contact angle and micromorphological analyses were also performed. Data were analyzed with Student's t-test (α = 5%). RESULTS: For both ceramic materials, HF+S resulted in higher mean µSBS (MPa) at baseline (LDC: HF+S 21.2 ± 2.2 > MEP 10.4 ± 2.4; FC: HF+S 19.6 ± 4.3 > MEP 13.5 ± 5.4) and after aging (LDC: HF+S 14.64 ± 2.31 > MEP 9 ± 3.4; FC HF+S: 14.73 ± 3.33 > MEP 11.1 ± 3.3). HF+S resulted in a statistically significant decrease in mean µSBS after aging (p = 0.0001), while MEP yielded no significant reduction. The main failure type was adhesive between composite cement and ceramic. HF+S resuted in the lowest contact angle. CONCLUSIONS: Hydrofluoric acid + silane resulted in higher mean µSBS than Monobond Etch & Prime for both ceramics; however, Monobond Etch & Prime had stable bonding after aging.

Fatigue failure load of feldspathic ceramic crowns after hydrofluoric acid etching at different concentrations.

STATEMENT OF PROBLEM: Hydrofluoric acid etching modifies the cementation surface of ceramic restorations, which is the same surface where failure is initiated. Information regarding the influence of hydrofluoric acid etching on the cyclic loads to failure of ceramic crowns is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the influence of different hydrofluoric acid concentrations on the fatigue failure loads of feldspathic ceramic crowns. MATERIAL AND METHODS: Eighty feldspathic ceramic crowns were cemented with resin cement to identical simplified complete crown preparations machined in a dentin-like polymer. The preparations were etched with 10% hydrofluoric acid for 60 seconds and received a primer coating. Before cementation, the intaglio of the ceramic crowns was treated with 1 of 4 surface conditionings (n=20): nonconditioned (control, CTRL), or etched for 60 seconds with different hydrofluoric acid concentrations: 1% (HF1), 5% (HF5), and 10% (HF10). A silane coupling agent was applied on this surface of all crowns, which were cemented to the preparations. Each crown was cyclically loaded in water with a G10 epoxy-glass piston positioned in the center of the occlusal surface. Fatigue failure loads of ceramic crowns were obtained by the staircase approach after 500000 cycles at 20 Hz. Mean failure loads were analyzed by 1-way ANOVA and the Tukey test (α=.05). RESULTS: Mean failure loads of groups CTRL (245.0 ±15.1 N), HF1 (242.5 ±24.7 N), and HF10 (255.7 ±53.8 N) were statistically similar (P>.05), while that of the HF5 group (216.7 ±22.5 N) was significantly lower (P<.05). CONCLUSIONS: HF5 acid had a negative effect on the fatigue loads of the tested feldspathic ceramic crowns, while HF1 and HF10 acids did not change the fatigue resistance.

The effect of extended glaze firing on the flexural fatigue strength of hard-machined ceramics.

STATEMENT OF PROBLEM: It is unclear whether an extended glaze firing could improve the long-term mechanical performance of densely sintered CAD-CAM ceramics. PURPOSE: The purpose of this in vitro study was to analyze the effect of an extended glaze firing on the flexural fatigue strength (FFS) of densely sintered milled (hard-machined) leucite-based (LEU) and lithium disilicate-based (DIS) ceramics. MATERIAL AND METHODS: Disks were machined from ceramic blocks and divided into 6 groups (n=20) according to the material, LEU or DIS, and to the applied glaze firing: manufacturer-recommended glaze (G group), extended glaze (EG group), and control/no firing (C group). The surface roughness of the disks was measured before and after firing by using a contact profilometer, and data were compared by paired sample tests. Specimens were submitted to fatigue by using the staircase test design in water (piston-on-3 balls; 500 000 cycles, 20 Hz, and sinusoidal loading). Mean (±SD) FFS values were then calculated and analyzed by using 1-way analysis of variance and post hoc Tukey test (α=.05). RESULTS: Surface roughness did not change after the firing (P>.05). The highest FFS value in both ceramics was obtained after EG firing (LEU-EG=80.52 ±6.3 MPa; DIS-EG=147.25 ±10.5 MPa), which was statistically superior to G firing (LEU-G=73 ±6.8 MPa, P=.003; DIS-G=134.34 ±15.6 MPa; P=.023) and C group (LEU-C=61.94 ±6.3 MPa; P<.001; DIS-C=134.13 ±17.3 MPa; P=.023). CONCLUSIONS: EG firing optimized the biaxial flexural fatigue strength of hard-machined leucite and lithium disilicate ceramics compared with conventional glaze firing.

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.

Simulation of CAD/CAM milling on lithium disilicate: Mechanical and topographic analyses of surface grinding different protocols.

The aim of this study was to evaluate the topography and the fatigue performance of lithium disilicate glass-ceramic after surface grinding through different laboratory protocols used to simulate the Computer-aided design/Computer-aided manufacturing (CAD/CAM) milling. Ceramic discs (IPS e.max CAD, Ø = 13.5 mm × 1.2 mm of thickness) were produced through different methodologies: milling in CAD/CAM system (CAD/CAM group); produced in-lab with a polished surface (POL group); or produced through in-lab methods and randomly distributed into five groups according to different grinding protocols to simulate the CAD/CAM milling [grinding with a CAD/CAM bur coupled to a mandrel (CAD/CAM Bur group); fine diamond bur using oscillatory movements (DBO group); fine diamond bur in x and y axes of the disc (DBXY group); #60-grit silicon carbide sandpaper (SiC group); and #60-grit wood sandpaper (WS group)]. The specimens were fatigue tested (n = 15) according to the step-stress method (initial load: 60 N; step-size: 20 N; 10,000 cycles/step; 20 Hz frequency). A roughness analysis was performed on all specimens, while fractal dimension (FD) and fractography were performed on representative samples. The Kaplan-Meier analysis showed that the POL (293.3 N) group presented better fatigue performance (higher load and number of cycles for failure) (p < 0.05) than the other groups (CAD/CAM = 222.7 N; CAD/CAM Bur = 181.3 N; DBO = 184.0 N; DBXY = 192.0 N; SiC = 182.6 N; WS = 182.6 N). For roughness, only the SiC (Ra = 1.616; Rz = 10.465) and WS (Ra = 1.673; Rz = 10.655) groups produced statistically similar Ra (µm) and Rz (µm) values to the CAD/CAM (Ra = 1.628; Rz = 9.571) group (p > 0.05). The surface created by CAD/CAM milling and POL group exhibited more complexity (FD) higher values than the experimental groups. For the ceramic surface topography images, the CAD/CAM milling visibly produced a uniform surface compared to the other groups; however, the POL group was the smoothest. The DBO, DBXY, SiC, and WS groups resulted in similar characteristics of surface topography. Therefore, although the SiC and WS groups showed similar roughness to the control group (CAD/CAM), no in-lab simulation method was fully capable to mimic the mechanical performance of the CAD/CAM-milled lithium disilicate glass-ceramic.

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.

Young's modulus and Poisson ratio of composite materials: Influence of wet and dry storage.

In the oral environment dental materials are subject to a wet condition what might in time change their elastic properties. In this article, we evaluated the influence of the storage condition (dry versus wet) on the Young's modulus and the Poisson ratio in compression of three composite materials. The data of the Young's modulus and Poisson ratio published of dental composite materials are not always comparable, due to different test methods and sample dimensions influencing the results. Therefore, we established the degree of exactness of the results out of the test set-up used. Since the present study depicted differences of the properties after dry and wet storage, the elastic properties should be measured after wet storage. The bonding between the matrix and the filler particles showed to have an influence on the elastic properties and on the influence of a wet environment.

Stable Resin Bonding to Y-TZP Ceramic with Air Abrasion by Alumina Particles Containing 7% Silica.

PURPOSE: To evaluate the influence of new air-abrasion powders with different silica concentrations (silica-coated aluminum oxide) and aging on the bond strength between composite cement and Y-TZP ceramic. MATERIALS AND METHODS: Ceramic slices (7 x 6.3 x 2 mm3) were randomly allocated into 8 groups (n = 20) considering different surface treatments (SiC: silica-coated aluminum oxide particles; AlOx: aluminum oxide particles; 7% Si and 20% Si: experimental powders consisting of 7% and 20% silica-coated of AlOx respectively) and aging (baseline: 24 h at 37°C in water; aged: 90 days at 37°C in water + 12,000 thermal cycles). A blinded researcher performed the air-abrasion procedure for 10 s (identical parameters for all groups). Composite resin cylinders (Ø = 3 mm) were cemented onto the silanized ceramic surfaces, light cured, and subjected to shear bond-strength testing (wire loop Ø = 0.5 mm). The topography of the powders and air-abraded surfaces was analyzed using SEM and atomic force microscopy (AFM). The elemental composition of the powders and air-abraded surfaces was analyzed with energy dispersive spectroscopy (EDS), and surface wetting of the air-abraded surfaces was also determined by contact-angle measurements. RESULTS: Under baseline conditions, all groups presented similar bond strengths, but only SiC and 7% Si yielded unaltered bond strength after aging. SiC and 7% Si presented lower contact angles. All groups presented similar surface topographies. The silica content was also similar among groups, except for AlOx. CONCLUSION: 7% Si and SiC presented similar bond strength and better bonding performance after aging than AlOx and 20% Si. A higher silica concentration was not able to promote stable adhesion of composite cement after aging.

Strength of a Zirconia-Reinforced Lithium Silicate Ceramic: Acid-Etching Time and Resin Cement Application Effects.

This study aimed to evaluate the effect of hydrofluoric (HF)-acid-etching time and the impact of a resin-cement layer on the biaxial flexural strength and structural reliability of a zirconia-reinforced lithium silicate (ZLS) glass ceramic. Disc-shaped specimens (n = 15) were divided according to: etching time (conditioning with 10% HF acid for 20, 40, and 60 seconds), and application of a resin-cement layer. Biaxial flexural, contact angle, and roughness analyses were performed. When the resin-cement layer was not present, flexural strength data increased with increasing etching times: 20 seconds = 250.8 MPa; 40 seconds = 278.4 MPa; 60 seconds = 342.9 MPa. Application of resin cement increased the strength values (20 seconds of acid etching on specimens with a resin-cement layer = 341.8 MPa). Different etching times did not affect the roughness of ZLS, and the contact-angle analysis presented lower values for 60 seconds of acid etching. The flexural strength of ZLS was only sensitive to surface changes when less exposure time was conducted. Longer etching times (40 and 60 seconds) should be considered for conditioning ZLS ceramic along with adhesive cementation.

Fatigue performance of adhesively cemented glass-, hybrid- and resin-ceramic materials for CAD/CAM monolithic restorations.

OBJECTIVE: To evaluate the fatigue failure load, number of cycles until failure, and survival probability of adhesively cemented materials with different microstructures (glass-, hybrid- and resin-ceramic) used to manufacture CAD/CAM monolithic restorations. METHODS: Disc-shaped specimens (n=15; Ø=10mm; thickness=1.0mm) were produced from CAD/CAM blocks as follows: feldspathic (FEL); leucite (LEU); lithium disilicate (LD); zirconia-reinforced lithium silicate (ZRLS); polymer-infiltrated ceramic network (PICN); and resin nanoceramic (RNC). Adhesive cementation was performed onto epoxy discs (dentin analogue- Ø=10mm; thickness=2.5mm). The cemented assemblies were subjected to fatigue testing using a step-stress approach (400N-2200N; step-size of 200N; 10,000 cycles per step; 1.4Hz). Fatigue data were analyzed using Kaplan-Meier and Mantel-Cox (log-rank) tests (p<0.05) and Weibull statistical analysis. Fractographic analysis was also performed. RESULTS: All RNC specimens survived the fatigue test (100% probability of survival at 2200N; 100,000 cycles) and presented occlusal deformation in response to loading, while all other tested materials failed in distinct loading steps with radial cracks starting from the bonding surface. LD (1146.7N; 47,333) and ZRLS (1013.3N; 40,666) materials obtained the highest fatigue failure loads and cycles until failure, meanwhile all PICN specimens failed during the first step (0% probability of survival at 400N; 10,000). FEL had similar Weibull modulus to LD and ZRLS and higher than LEU for both load and number of cycles outcomes. SIGNIFICANCE: The microstructure of adhesively cemented glass-, hybrid- and resin-ceramic CAD/CAM restorative materials influence their response during fatigue testing, which aids in suggesting the best clinical indications.

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.

Effect of zirconia polycrystal and stainless steel on the wear of resin composites, dentin and enamel.

This study evaluated the effect of two antagonist substrates (Y-TZP/zirconia or stainless steel) on the wear rate and surface alterations of different composite materials and bovine tooth substrates (enamel and dentin). The wear rate of different composite materials (n = 20; two direct composite resins: HelioMolar - HM; Clearfil AP-X - CAP, three indirect composite resins: Estenia C&B - EST; Adoro - ADO; Sinfony - SFY, and one composite resin for direct/indirect restorations: Filtek Z250 - Z250), bovine enamel and dentin against two different antagonist materials (zirconia or stainless steel) into two mediums (two-body and three-body wear) were collected. After wear tests on ACTA wear machine, Scanning Electron Microscopy (SEM) analysis was performed to access the surface alterations. The wear data were evaluated by three-way ANOVA and Tukey post-hoc test (α = 0.05). The factors 'antagonist', 'medium', 'restorative materials', and the interaction of all factors grouped by two and integrated showed statistical significance on the wear rates. A two-body test depicted no difference among all composites and enamel for wear rate, while a three-body test depicted differences among composites directly related to the filler content: EST < Z250 = CAP < ADO = HM < SFY. Dentin always showed the highest wear rates and enamel the lowest rates. The presence of food bolus (three-body test) led to higher wear rates in comparison to an only aqueous medium (two-body test). SEM analysis showed that different materials present specific wear patterns, regardless of the medium and the antagonist considered. Differently from enamel, dentin substrate was intensively prone to wear, regardless of the antagonist/medium. Resin composite substrates presented intermediate wear rates, depending directly on their filler content (% in weight).

Sequential usage of diamond bur for CAD/CAM milling: Effect on the roughness, topography and fatigue strength of lithium disilicate glass ceramic.

The aim of this study was to evaluate the effect of sequential usage (milling order) of CAD/CAM diamond burs on the surface roughness, topography and fatigue performance of a lithium disilicate glass-ceramic. Seventy-two (72) ceramic discs (Ø= 13.5 mm; thickness= 1.2 mm; IPS e.max CAD) were milled using four pairs of burs and allocated into three groups (n = 24) according to the milling sequence: 1 through 6 (1-6), 7 through 12 (7-12), and 13 through 18 (13-18). The burs were evaluated under SEM at the different milling stages to depict any degradation generated by the milling sequence. Fatigue performance was assessed by a stepwise approach (initial strength of 20 MPa for 5000 cycles; incremental steps of 20 MPa for 20,000 cycles each until fracture; frequency of 20 Hz) using the ISO 6872:2015 recommendation for piston-on-three-balls biaxial flexure strength tests. Surface roughness, topography analysis and fractography of the failed discs were also performed. Survival analysis (Kaplan-Meier and Mantel-Cox post hoc test) showed that the milling sequence had no effect on the fatigue strength (190 - 201 MPa) or the number of cycles until fracture (174,958 - 180,087 cycles). Ceramic topography and roughness (Ra, Rz and RSm parameters) were similar among the groups, even though SEM analysis depicted CAD/CAM diamond burs degraded over time. Fractography evidenced all failures starting from surface defects introduced by milling at the samples' tensile side. The sequential usage of CAD/CAM diamond burs (milling order) does not affect the lithium disilicate surface roughness, topography or fatigue performance.

Lithium disilicate glass-ceramic vs translucent zirconia polycrystals bonded to distinct substrates: Fatigue failure load, number of cycles for failure, survival rates, and stress distribution.

The present study evaluated the fatigue behavior of monolithic translucent zirconia polycrystals (TZ) and lithium disilicate glass-ceramic (LD) bonded to different substrates. Disc-shaped specimens of ceramic materials TZ and LD were bonded to three substrates with different elastic modulus (E) (fiber-reinforced composite (FRC) - softest material, E = 14.9 GPa; titanium alloy (Ti) - intermediary properties, E = 115 GPa; and zirconia (Yz) - stiffest material, E = 210 GPa). The surfaces were treated and bonded with resin cement (disc-disc set-up). Fatigue testing followed a step-stress approach (initial maximum load = 200 N for 5000 cycles, incremental step load = 200 N for 10,000 cycles/step). The fatigue failure load and number of cycles until failure were recorded and statistically analyzed. Fractographic and finite element (FEA) analyzes were conducted as well. TZ ceramic depicted higher fatigue failure load, number of cycles until failure, and survival probabilities than LD, irrespective of the substrate. Moreover, TZ and LD presented better fatigue behaviors when bonded to substrates Ti and Yz in comparison to FRC. FEA revealed lower tensile stresses at restorative material when bonded to stiffer substrates. Fractography showed that the fracture origin started at bottom surface of restorative material (except for TZ bonded to Yz, in which crack initiated at load contact point). Translucent zirconia polycrystals present superior mechanical behavior than lithium disilicate glass-ceramic. The substrate type influences the mechanical performance of monolithic dental ceramics (stiffer substrates lead to better fatigue behavior).

Air-abrasion using new silica-alumina powders containing different silica concentrations: Effect on the microstructural characteristics and fatigue behavior of a Y-TZP ceramic.

This study assessed the fatigue performance (biaxial flexure fatigue strength), surface characteristics (topography and roughness) and structural stability (t-m phase transformation) of a Y-TZP ceramic subjected to air-abrasion using new powders (7% and 20% silica-coated aluminum oxide particles) in comparison to commercially available powders. Disc-shaped specimens were manufactured (ISO 6872-2015) and randomly allocated into four groups considering the air-abrasion materials: SiC: commercially available silica-coated aluminum oxide; AlOx: commercially available aluminum oxide; 7%Si and 20%Si: experimentally produced materials consisting of 7% and 20% silica-coated AlOx, respectively. Air-abrasion was executed by a blinded researcher (1 cm distance from the tip to the specimen surface, under 2.8 bar pressure for 10 s). The fatigue tests (n = 15) were performed by the staircase method under a piston-on-three-balls assembly. Topography and roughness assessments (n = 30) of abraded samples and fractography of failed discs were performed. The highest fatigue strength (MPa) was observed for 7%Si (887.20 ±â€¯50.54) and SiC (878.16 ±â€¯29.81), while the lowest fatigue strength for 20%Si (773.89 ±â€¯46.44) and AlOx (796.70 ±â€¯46.48). Topography analysis depicted similar surface morphology for all conditions. However, roughness (µm) was only statistically different between 7%Si (Ra = 0.30 ±â€¯0.09; Rz = 2.31 ±â€¯0.63) and SiC (Ra = 0.26 ±â€¯0.04; Rz = 1.99 ±â€¯0.34). Monoclinic phase grains appeared on Y-TZP surface in a similar content (≈11-12%) for the protocols. Fractography showed all failures starting on air-abraded surface/sub-surface defects from the tensile side. In terms of roughness, phase transformation and fatigue, the new 7% silica-coated aluminum oxide presented similar behavior to the commercially available powder. Increasing silica-coating concentration to 20% did not lead to a gentle air-abrasion protocol.

Adhesion to a Lithium Disilicate Glass Ceramic Etched with Hydrofluoric Acid at Distinct Concentrations.

This study evaluated the effect of different hydrofluoric acid (HF) concentrations on the bond strength between a lithium disilicate-based glass ceramic and a resin cement. Eighty ceramic-blocks (12×7×2 mm) of IPS e.Max CAD (Ivoclar Vivadent) were produced and randomly assigned to 8 groups, considering 2 study factors: HF concentration in 4 levels, i.e., 1% (HF1), 3% (HF3), 5% (HF5), and 10% (HF10), and storage in 2 levels, i.e., baseline (tests were performed 24 h after cementation), and aged (storage for 150 days + 12,000 thermal-cycles at 5°C and 55°C). Acid etching (20 s) was performed, followed by washing, drying, and silanization. Four resin cement cylinders (ϕ= 0.96 mm) were built-up from starch matrices on each ceramic sample (n= 40). Additional ceramic samples were etched and analyzed for contact angle, micro-morphology, and roughness. In baseline condition (without aging), the HF3, HF5, and HF10 groups showed similar bond strength values (13.9 - 15.9 MPa), and HF1 (11.2 MPa) presented lower values than HF5, being that statistically different (p= 0.012). After aging, all the mean bond strengths statistically decreased, being that HF3, HF5, and HF10 (7.8 - 11 MPa) were similar and higher than HF1 (1.8 MPa) (p= 0.0001). For contact angle, HF3, HF5, and HF10 presented similar values (7.8 - 10.4°), lower than HF1 and CTRL groups. HF5 and HF10 presented rougher surfaces than other conditions. For better bond strength results, the tested ceramic may be etched by HF acid in concentrations of 3%, 5%, and 10%.

The effect of hydrofluoric acid concentration on the fatigue failure load of adhesively cemented feldspathic ceramic discs.

OBJECTIVE: This study investigated the influence of hydrofluoric acid (HF) etching at different concentrations on the fatigue failure load of adhesively cemented feldspathic ceramic discs (Vita Mark II). Besides, their effect on the micromorphology of ceramic surface was investigated. METHODS: Eighty ceramic discs (ϕ=10 mm; thickness=1.5 mm) were cemented to epoxy supporting discs (ϕ=10 mm; thickness=2.0mm) using different surface conditioning methods (n=20): nonetched control (CTRL), or etched for 60s with different HF concentrations: 1% (HF1), 5% (HF5), or 10% (HF10). All the ceramic discs received a silane application (Monobond Plus). The epoxy discs were etched with 10% HF for 60s and received a primer coating (Multilink Primer A+B). Adhesively cementation was performed (Multilink Automix), and the assemblies (ceramic discs/epoxy discs) were subjected to cyclic loads in water by a staircase approach (500,000 cycles; 20Hz; initial load=290N; step size=30N). Fatigue failure load data were analyzed using 1-way ANOVA and post-hoc Tukey's tests (α=.05). RESULTS: Mean failure load of the HF5 group (255.0±23.0N) was significantly lower; HF1 group (301.7±71.0N) presented intermediate values, and the highest values were achieved in CTRL (351.7±13.4N) and HF10 (341.7±20.6N) groups. All the failures were radial cracks starting from the bonding surface. SIGNIFICANCE: In terms of fatigue failure load, etching with 1% and 5% HF had a deleterious effect on the fatigue behavior of an adhesively cemented feldspathic ceramic, while 10% HF had no negative influence.

Internal adjustments decrease the fatigue failure load of bonded simplified lithium disilicate restorations.

OBJECTIVE: To investigate the effect of intaglio surface adjustment of simplified lithium disilicate ceramic restorations adhesively cemented to a dentin-like material on its fatigue behavior. METHODS: Ceramic discs (IPS e.max CAD) were prepared and an in-Lab simulation of machining roughness was performed by grinding with SiC paper (#60). Ceramic discs were divided into 4 groups according to the internal adjustment of the cementation surface: no adjustments (CTRL); adjustment with a medium (M), fine (F), or extra fine (FF) diamond bur. Dentin-like material discs were also produced. Ceramic disc intaglio surfaces were etched (5% hydrofluoric acid; 20s) and received a silane coating. Dentin-like material discs were etched (10% hydrofluoric acid; 1min) and received a primer coating. Pairs of ceramic/dentin-like material were adhesively cemented (Multilink Automix), and fatigue failure load tests were performed using the Staircase approach (250,000 cycles; 20Hz). Roughness, topographic and fractographic analyses were performed. Statistical analyses were carried out through ANOVA tests. RESULTS: All ground groups (M=521.3 N; F=536.9 N; FF=676.2 N) presented lower fatigue failure load values than the control (1241.6 N). M diamond bur created a rougher surface than F (Ra and Rz parameters). However, FF was similar to F and M for Ra, and similar to F for Rz. SIGNIFICANCE: Bur adjustments on the intaglio surface of simplified lithium disilicate ceramic restorations greatly decreased the fatigue failure load even using an extra-fine diamond bur. Care should be taken when internal adjustments are needed.