Investigation of the effect of different aging methods on the structural properties of monolithic translusent zirconia

The aim of this study is to evaluate the effects of different aging methods on the flexural strength, phase transformation, hardness value and fracture toughness of monolithic zirconia material with high translucency. 84 disc-shaped specimens of ultra-translucent monolithic zirconia material (VITA YZ XT) produced by CAD/CAM method were prepared. According to the aging methods of the samples; they were divided into 7 different groups: 2 hours rapid aging, 6 hours rapid aging, 12 hours rapid aging, thermal cycle, thermomechanical aging under 50 N force, thermomechanical aging under 100 N force and non-aged control group (n=12). 134 oC temperature and 2 bar pressure parameters were applied to the rapid aging groups. In the thermal cycle group, water cycles at a temperature of 5-55 oC and 50.000 cycles with a waiting time of 30 seconds were applied. In thermomechanical aging groups, 1.200.000 cycles were applied at 1.7 Hz frequency. Biaxial bending strength, Vickers hardness values and fracture toughness values of 7 groups were calculated. SEM analyzes were applied to one sample from each group and XRD analyzes to two samples from each group. Data were analyzed with Kolmogrov Smirnov, Kruskal-Wallis and Dunn tests. The variability of the flexural strength values was analyzed using the Weibull distribution function and the Weibull modulus (m) and characteristic strengths (σo) were calculated for each group and Weibull distribution graph created. The chewing simulator 50 N, 100 N, and 12 h rapid aging groups showed higher flexural strength than the control, 2 h rapid aging and 6 h rapid aging groups (p<0.05). In paired comparisons, no significant difference was found between the thermal cycle group and any group (p>0.05). No significant change was observed between the control and aging groups in terms of hardness and fracture toughness. According to the Weibull distribution analysis, the thermo cycle group showed a lower m value than the other groups, no significant difference was found between the other groups. According to the XRD findings, no aging procedure resulted in a significant increase in the monoclinic phase rate. Keywords: Artificial aging, zirconia, translucent.