Influence of Heat Treatment on the Fracture Toughness and Microstructure of Zirconia Ceramics: An In Vitro Study

Abstract

The aim of this study was to evaluate the impact of heat treatment on the fracture toughness and surface roughness of zirconia ceramics. Forty disks were performed from zirconia blocks using CAD/CAM technology and distributed into 4 groups according to the frequency of the heat treatments (n = 10). Group HT0: without heat treatment (control group). Group HT1: One time heat treatment according to the first step of the veneering procedures. Group HT5: heat-treated 5 times to replicate the complete veneering process. Group HT7: heattreated 7 times to represent the complete veneering process plus 2 correction firings. A hardness testing apparatus was used to measure the fracture toughness, and the surface roughness was evaluated. Data was analyzed by using 1-way ANOVA, and the Pearson correlation coefficient was used to define the significant correlation between fracture toughness and surface roughness (α = 0.05). No significant difference was found in the mean fracture toughness (KIC) of the tested groups (P > 0.05). Furthermore, no significant difference was observed in the mean surface roughness (Ra) of the tested groups (P > 0.05). No statistically significant correlation between surface roughness and fracture toughness in any group was detected (P > 0.05). Within the limitation of the current laboratory study, a heat treatment showed no influence on the fracture toughness (KIC) and surface roughness (Ra) values of zirconia ceramics.