Effect of different loading pistons on stress distribution of a CAD/CAM silica-based ceramic: CAD-FEA modeling and fatigue survival analysis.

Abstract

This study evaluated the effect of different loading pistons, made of various materials and with different elastic moduli acting as antagonist material, on stress distribution and fatigue behavior of a CAD/CAM silica-based ceramic. Discs of CAD/CAM made silica-based ceramic (N = 60) (VITA MARK II) were divided into six groups (n = 10 per group), according to the test method (M: Monotonic; F: Fatigue) and the antagonist piston material (T: Tungsten; S: Steel; G: Epoxy resin). FT, FS and FG combinations were submitted to mechanical cycling (2 × 10⁶ cycles, 4 Hz, 45 N). The bending stress after fatigue were also valuated using Weibull analysis and the parameters η (eta), β (beta) and the mean time to failure (MTTF) were calculated. Fractographic analysis and Finite Element Analysis (FEA) were performed. Data were analyzed using ANOVA and Tukey's tests (alpha=0.05). MG presented significantly less bending strength (MPa) (75.6) compared to MT (87.8) and MS (84.4) (p < 0.05). Six specimens from FT (MMTF: 8.3 × 10⁶; β:0.60; η:5.6 × 10⁶), four from FS (MMTF: 1.9 × 10⁶; β:1.2; η:2.0 × 10⁶) and one from FG (MMTF: 1.3 × 10⁶; β:0.48; η:0.64 × 10⁶) survived the fatigue test. The stress peak on the tensile surface of S was similar to that of T and both were less than that of G. The failure origins were on the tensile surface. The epoxy resin pistons were able to decrease the bending stress, and life expectancy (faster failure) of a silica-based ceramic compared to tungsten and steel.