CONCLUSION: Compared to control, thermal and mechanical

Abstract

The purpose of this study was to evaluate theeffect of thermal and mechanical aging on the fracturetoughness of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) core materials.MATERIALS ANDMETHOD: Disc-shaped specimens for eachcore material (diameter: 15 mm, thickness: 1.2 mm), Cercon Base and Lava Plus, were randomly divided into threegroups (control, thermal aging and mechanical aging). Noaging was applied to control specimens. Thermal aginggroup specimens were subjected to 104thermal cycles inwater between 5-55 °C (dwell time of 30 s). Mechanicalaging group specimens were subjected to a 200 N load for105times, with a frequency of 2 Hz. The fracture toughnessof the control, thermal and the mechanical aging groupswere measured by using the indentation fracture technique. Ten indentations were performed for each material.After each indentation, microscopic readings wererecorded 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 controlgroup of Cercon Base and the aging groups (p>0.05). However, significant difference was found between the thermaland the mechanical aging groups of Cercon Base (p0.05)