Effect of fatigue on biaxial flexural strength of bilayered porcelain/zirconia (Y-TZP) dental ceramics

Abstract

Objectives. The aim of this study was to evaluate the effect of fatigue on biaxial flexural strength of bilayered disks of two Y-TZP cores. Methods. Twenty bilayered veneer/zirconia disks were fabricated from each material (Lava veneer + core, 3 M/ESPE, and Cercon veneer + core, Densply). Ten specimens from each material were tested for biaxial flexural strength either with or without being subjected to fatigue (20,000 cycles, 2 Hz, 200 N load) in a universal testing machine (1 mm/min). Stresses generated at the core and the veneer, at the top and the bottom surfaces, and the interface of bilayered disk were calculated using Huesh's solutions. Data were statistically analyzed using Weibull statistics. The fractured core was also examined via Raman spectroscopy and the monoclinic fraction was calculated at the top, the middle of thickness, and the bottom of the cross-section of fractured core. The results of monoclinic fraction were statistically analyzed by Three-Factor ANOVA with Repeated Measures on One Factor. Results. Weibull modulus (m) of Cercon control (CC), Cercon fatigue (CF), Lava control (LC) and Lava fatigue (LF) were between 11.8 and 14.3, 7.1 and 13.1, 9.4 and 13, and 7.1 and 8.2, respectively. There were no significant differences between characteristic strength (sigma(0)) of CC (970.9 MPa) and CF (947.7 MPa) (p > 0.05). For Lava, sigma(0) of LF (1444.8 MPa) was significantly higher than LC (1240.5 MPa) (p < 0.05). At the interfaces, sigma(0) values of CC and CF groups were not significantly different while LF showed significantly higher sigma(0) than LC. The monoclinic zirconia was significantly lower for CF than CC and significantly higher for LF than LC. Significance. Fatigue showed different effects on the strength of Cercon and Lava ceramic systems. Decreases in m values were observed at the interfaces of two materials after fatigue.