摘要：OBJECTIVE: The purpose of this study was to evaluate the effect of thermal and mechanical aging on the fracture toughness of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) core materials. MATERIALS AND METHOD: Disc-shaped specimens for each core material (diameter: 15 mm, thickness: 1.2 mm), Cercon Base and Lava Plus, were randomly divided into three groups (control, thermal aging and mechanical aging). No aging was applied to control specimens. Thermal aging group specimens were subjected to 10 4 thermal cycles in water between 5-55 °C (dwell time of 30 s). Mechanical aging group specimens were subjected to a 200 N load for 10 5 times, with a frequency of 2 Hz. The fracture toughness of the control, thermal and the mechanical aging groups were measured by using the indentation fracture technique. Ten indentations were performed for each material. After each indentation, microscopic readings were recorded and the fracture toughness was calculated according to an established formula. Results were statistically analyzed by using a two-way analysis of variance (ANOVA) test. RESULTS: Indentation fracture toughness values of the control, the thermal and the mechanical aging groups of Cercon Base were 6.28, 6.39 and 6.02 MPa√m, respectively. There was no significant difference between the control group of Cercon Base and the aging groups (p>0.05). However, significant difference was found between the thermal and the mechanical aging groups of Cercon Base (p<0.05). Indentation fracture toughness values of the control, the thermal and the mechanical aging groups of Lava Plus were 4.79, 4.76 and 4.91 MPa√m, respectively. Again, there was no significant difference between the control the aging groups of Lava Plus (p>0.05). CONCLUSION: Compared to control, thermal and mechanical aging had no significant effect on the fracture toughness of the different Y-TZP core materials.
