The comparison of strengths between the zirconia which have diffeerent translucency levels after the thermal and mechanical aging

Due to the change in today's aesthetic perception, new materials are tried to be developed that are both aesthetically acceptable and provide sufficient resistance to chewing forces. Monolithic zirconium restorations are an alternative to zirconium-based and metal-supported restorations with their high fracture strength, natural tooth-like abrasion on the opposite tooth, and aesthetics. By changing the translucency parameters, it has been tried to produce both improved optical properties and more durable monolithic zirconium materials for the anterior and posterior regions. For this purpose, Katana High Translucent, Katana Ultra Translucent Multi Layered and UPCERA blocks were used in our study where we compared the biaxial bending strength of zirconiums with different translucencies before and after thermal and mechanical aging. These blocks were produced in 1.2 mm diameter and 16 mm thickness discs in accordance with ISO 6872 standards in the form of 40 discs in each group and a total of 120 discs. Each group was divided into four subgroups (N=10); One group was aged with 10.000 thermal cycles between 5 °C and 55 °C, one group was aged with a chewing simulator at 50 N load for 240.000 cycles, and one group with both thermal cycle and chewing simulator. Biaxial bending strength and Vicker's hardness values of a total of 12 groups were compared. SEM / EDS analysis of random samples from each group was performed. The data were analyzed by Shapiro Wilk's (p = 0.05) and Mann Whitney U and Kruskal Wallis H tests. The relationship between biaxial bending strength and Vickers hardness values was found to be significantly different for Katana UTML, Katana HT and UPCERA groups. In the tests, the lowest fracture strength value was found in Katana UTML discs, while the highest strength was measured in UPCERA groups. Vickers hardness value was found the highest in Katana UTML group, while the lowest was found in Katana HT groups. It was observed that the aging procedures did not make a statistically significant difference in terms of fracture strength and Vickers hardness. It was determined that the fracture strength of zirconias with different translucency is suitable for oral use. According to the results of the SEM analysis, there was no deformation that would cause surface deterioration in the groups after artificial aging. According to the EDS analysis results, the highest ytrium ratio was observed in Katana UTML groups, while the lowest was found in UPCERA groups. Keywords: Biaxial bending strength, translucent, zirconia