Effect of position within a blank and thermo-mechanical aging on fracture force and failure mode of strength-gradient multilayer zirconia crowns

Abstract

PURPOSE. This study aimed to investigate the effects of blank position and thermo-mechanical aging on the fracture force of strength-gradient multilayer (SGM) zirconia crowns. MATERIALS AND METHODS. Eighty premolar SGM zirconia crowns (KATANA™ Zirconia YML) were assigned to eight groups (n = 10), based on four blank positions (1, 2, 3, and 4 mm below the top edge) and two conditions (with and without thermo-mechanical aging). Aging simulated five years of clinical service through 6, 000 thermocycles (5°C - 55°C) and cyclic fatigue (50 N, 1.2 Hz, 1, 200, 000 cycles). Fracture force was measured using a universal testing machine. Failure modes and fractographic features were examined. Data were assessed using two-way ANOVA, Bonferroni post hoc tests, independent t-tests, and Spearman correlation (P