Mechanical behavior and adhesive potential of glass fiber-reinforced resin-based composites for use as dentin analogues.

PURPOSE: To characterize experimental glass fiber-reinforced resin-based composites (GFIR-isophthalic; and GFOR-orthophthalic), evaluating their mechanical behavior and adhesive potential to ceramic in comparison to human dentin and a traditional glass fiber-reinforced epoxy resin (G10). METHODS: Density (ρ), elastic modulus (E), and Poisson's ratio (ν) were evaluated using 2 mm thick specimens from GFIR, GFOR, human dentin and G10. Biaxial flexural strength (δf), Knoop hardness and surface topography under scanning electron microscopy (SEM) were assessed for GFIR and GFOR specimens. G10 was also tested for δf. For the adhesive potential, ceramic specimens (n=10) bonded to GFIR, GFOR or human dentin were tested for microtensile bond strength (MTBS). Disc-shaped ceramics were cemented onto dentin, GFIR, GFOR and G10 (n=15) and loaded to failure. Data were statistically evaluated using Weibull, ANOVA, and Tukey's test (α=0.05). RESULTS: The experimental resins (GFIR and GFOR) showed similar values of HK (53.1 and 52.7 GPa), (ν (0.44 and 0.43) and δf (41.2 MPa and 40.7 MPa). Considering the human dentin values for ρ and E, the corresponding values obtained from GFIR, GFOR and G10 were different, with GFOR values being closer to dentin than GFIR and G10. G10 had statistically greater(δf than GFIR and GFOR. Mean bond strength of ceramic to GFIR, GFOR and dentin were statistically similar. The fracture load of resin-cemented ceramic was influenced by substrate. CLINICAL SIGNIFICANCE: The experimental materials (GFIR and GFOR) showed similar adhesion characteristics to human dentin, however GFOR showed a better potential to be used as a dentin analogue.

Bond strength between composite repair and polymer-infiltrated ceramic-network material: Effect of different surface treatments.

OBJECTIVE: To evaluate the bond strength of a polymer-infiltrated ceramic-network (PICN) material and to composite repair after different surface treatments. MATERIALS AND METHODS: Eighteen blocks of the PICN material were obtained from CAD/CAM blocks, aged and randomly divided into 2 groups: 5% hydrofluoric acid (HF) or sandblasting with aluminum oxide particles (SAND). For each condition, three treatments were tested: silane (Sil), silane-containing adhesive (Ad), or silane + silane-containing adhesive (SilAd). The treated PICN surfaces were restored with composite resin. The microtensile bond strength test was performed in a universal testing machine, and data (MPa) were compared with two-way Analysis of variance (anova) and Tukey (α = 0.05). Roughness (Ra) and contact angle (CA) were obtained after HF and SAND conditions. RESULTS: The greatest bond strength values were obtained for the groups Sil and SilAd, for both HF and SAND pretreatments. The Ra values of SAND were statistically greater than HF. The CA generated by the adhesive on SAND surface was lower than HF surface. CONCLUSIONS: The use of silane improves the bond strength of the composite repair to PICN substrate compared to the single use of silane-containing adhesive. The HF pretreatment is most indicated when the silane-containing adhesive is applied alone. CLINICAL SIGNIFICANCE: Fractured PICN restorations can be repaired with composite resin, because the surface is treated with hydrofluoric acid or sandblasting followed by the individual use of silane.

Precision of different fatigue methods for predicting glass-ceramic failure.

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

How does the piston material affect the in vitro mechanical behavior of dental ceramics?

STATEMENT OF PROBLEM: Variables involving the indication, manufacturing, and clinical use of ceramic restorations make the standardization of in vitro studies a challenge and raise questions as to the clinical validity of the resulting data. PURPOSE: The purpose of this in vitro study was to assess the effect of piston material on the fracture behavior of ceramics tested under compressive load. MATERIAL AND METHODS: Two ceramics were evaluated: a lithium disilicate-based glass-ceramic (D) and a feldspathic porcelain (P). Plate-shaped ceramic specimens (1.5-mm thick) were adhesively cemented onto a dentin analog substrate. The specimens from each ceramic were divided into 4 groups according to the piston material (n=20): metal (M) (stainless steel), composite resin (R) (NEMA-G10, fiber-reinforced epoxy resin), ceramic (C) (lithium disilicate-based glass-ceramic), and human tooth (T) (canine). A gradual compressive load (0.5 mm/min) was applied to the center of the specimen with a universal testing machine. The test was performed in 37°C distilled water, and the initial crack was detected by using an acoustic system. The fracture load values (N) were statistically analyzed with the Kruskal-Wallis and Dunn tests (α=.05). A finite element analysis (FEA) was also performed. RESULTS: Piston material had no influence on fracture load and failure mode of ceramic D. Ceramic P showed higher fracture load values when loaded with the composite resin piston. Ceramic P showed more combined failures (cone crack and radial crack) than D. The FEA showed a distinct stress distribution for R piston on P. Pistons C and T resulted in similar stress distribution, fracture load, and failure mode for both ceramics. CONCLUSIONS: The effect of piston material on the ceramic fracture behavior depends on the ceramic being evaluated.

How oral environment simulation affects ceramic failure behavior.

STATEMENT OF PROBLEM: Investigating the mechanical behavior of ceramics in a clinically simulated scenario contributes to the development of new and tougher materials, improving the clinical performance of restorations. The optimal in vitro environment for testing is unclear. PURPOSE: The purpose of this in vitro study was to investigate the failure behavior of a leucite-reinforced glass-ceramic under compression loading and fatigue in different simulated oral environment conditions. MATERIAL AND METHODS: Fifty-three plate-shaped ceramic specimens were produced from computer-aided design and computer-aided manufactured (CAD-CAM) blocks and adhesively cemented onto a dentin analog substrate. For the monotonic test (n=23), a gradual compressive load (0.5 mm/min) was applied to the center of the specimens, immersed in 37ºC water, using a universal testing machine. The initial crack was detected with an acoustic system. The fatigue test was performed in a mechanical cycling machine (37ºC water, 2 Hz) using the boundary technique (n=30). Two lifetimes were evaluated (1×106 and 2×106 cycles). Failure analysis was performed using transillumination. Weibull distribution was used to evaluate compressive load data. A cumulative damage model with an inverse power law (IPL) lifetime-stress relationship was used to fit the fatigue data. RESULTS: A characteristic failure load of 1615 N and a Weibull modulus of 5 were obtained with the monotonic test. The estimated probability of failure (Pf) for 1×106 cycles at 100 N was 31%, at 150 N it was 55%, and at 200 N it was 75%. For 2×106 cycles, the Pf increased approximately 20% in comparison with the values predicted for 1×106 cycles, which was not significant. The most frequent failure mode was a radial crack from the intaglio surface. For fatigue, combined failure modes were also found (radial crack combined with cone crack or chipping). CONCLUSIONS: Fatigue affects the fracture load and failure mode of leucite-reinforced glass-ceramic.

Characterization of a polymer-infiltrated ceramic-network material.

OBJECTIVES: To characterize the microstructure and determine some mechanical properties of a polymer-infiltrated ceramic-network (PICN) material (Vita Enamic, Vita Zahnfabrik) available for CAD-CAM systems. METHODS: Specimens were fabricated to perform quantitative and qualitative analyses of the material's microstructure and to determine the fracture toughness (KIc), density (ρ), Poisson's ratio (ν) and Young's modulus (E). KIc was determined using V-notched specimens and the short beam toughness method, where bar-shaped specimens were notched and 3-point loaded to fracture. ρ was calculated using Archimedes principle, and ν and E were measured using an ultrasonic thickness gauge with a combination of a pulse generator and an oscilloscope. RESULTS: Microstructural analyses showed a ceramic- and a polymer-based interpenetrating network. Mean and standard deviation values for the properties evaluated were: KIc=1.09±0.05MPam(1/2), ρ=2.09±0.01g/cm(3), ν=0.23±0.002 and E=37.95±0.34GPa. SIGNIFICANCE: The PICN material showed mechanical properties between porcelains and resin-based composites, reflecting its microstructural components.

Influence of Y-TZP ceramic treatment and different resin cements on bond strength to dentin.

OBJECTIVES: Evaluating the bond strength (σ) of resin cement systems (RXA - RelyX ARC; RXU - RelyX U100; and PF - Panavia F) to dentin and yttria-stabilized zirconia-based ceramic (YZ - In-Ceram YZ) after different surface treatments and aging. METHODS: Occlusal dentin of 54 human molars was exposed and conditioned following manufacturers' instructions. Fifty-four YZ blocks were sintered and divided into two groups according to surface treatment: PA - airborne particle abrasion, and SC - tribochemical silica coating. All treated YZ blocks were cemented to dentin using one of the cement systems (RXA, RXU, and PF) following manufacturers' recommendations, which includes specific silane agents. Teeth-cement-ceramic blocks were stored in 37°C distilled water for 24h before cutting into non-trimming bar-shaped specimens (adhesive area, A=1±0.1mm(2)). Specimens (n≥12) were assigned to one of the following conditions: N - no storage; W - stored in 37°C distilled water for 60days; and TC - thermal cycling (5-55°C; 10,000 cycles). All specimens were loaded in tension (F) to failure using a universal testing machine. The σ (F/A) was calculated and data were statistically analyzed using ANOVA and Tukey tests (α=0.05). Fracture surfaces were examined to determine the failure mode. RESULTS: RXA-SC and PF-PA specimens showed the greatest mean σ values after N (13.9 and 13.0MPa, respectively) and TC (12.9 and 14.8MPa, respectively). SC-treated showed greater mean σ values than PA-treated YZ specimens after W. SIGNIFICANCE: Regardless of the cement used, W and TC did not significantly reduce the σ of SC-treated YZ resin bonded to dentin.