Mechanical performance of Y-TZP monolithic ceramic after grinding and aging: Survival estimates and fatigue strength

Abstract

This study aims to evaluate the flexural fatigue strength and survival estimates of an Y-TZP monolithic ceramic after grinding and aging. Ceramic discs (1.2 mm thickness × 15.0 mm diameter - ISO, 6872, 2015) of zirconia (Zirlux FC2 – Ardent; Ivoclar Vivadent) were made and randomly allocated into 6 groups (n = 10), according to grinding and aging factors: Ctrl – as-sintered; Ctrl Sto – as-sintered and dry stored at room temperature for 2 years; Ctrl Aut Sto – as-sintered, submitted to autoclaved aging (134 °C, 2 bar, 20 h) and then dry stored for 2 years; and similar conditions for ground samples (Ground; Ground Sto; Ground Aut Sto). Grinding was performed with diamond burs (#3101G, KG Sorensen) coupled to a contra-angle torque multiplier attached to a low speed motor under constant irrigation. Fatigue testing followed a step-stress approach. Data from strength and number of cycles until fracture were recorded and analyzed through Kaplan-Meier and Mantel-Cox tests. Both grinding and aging increase monoclinic phase content. The topography was altered by grinding but not by aging procedures. Grinding did not alter the fatigue strength (Ctrl = Ground), while aging increase it only for ground groups (Ground Sto, Ground Aut Sto). Aged conditions (Ctrl Sto; Ground Sto; Ctrl Aut Sto; Ground Aut Sto) showed increased survival probabilities for both flexural fatigue strength and cycles for failure. Therefore, despite promoting monoclinic phase increase, aging and grinding did not deleteriously affect the fatigue behavior of Y-TZP ceramics.