Effects of Pretreatment, Specimen Thickness, and Artificial Aging on Biaxial Flexural Strength of Two Types of Y-TZP Ceramics

Objectives: To evaluate the effects of surface treatment, specimen thickness, and aging on the biaxial flexural strength (BFS) of two types of yttria-stabilized, tetragonal zirconia polycrystal (Y-TZP) ceramics. Methods and Materials: Disc-shaped specimens, 0.4 and 1.3 mm thick, made from hot isostatic pressed (Denzir) and non-hot isostatic pressed (ZirPlus) Y-TZP, were sandblasted, heat treated, and autoclaved. The surface topography was assessed in accordance with European Standard 623-624:2004 and the BFS tests in accordance with International Organization for Standardization Standard 6872:2008. For statistical analyses, one-way Shapiro-Wilk test, analysis of variance (post hoc: least significant differences), Mann-Whitney U-test, and Pearson correlation tests (p<0.05) were used. Results: As delivered, the BFS of the 0.4-mm ZirPlus was >1.3-mm ZirPlus (p<0.01), and the BFS of the 0.4-mm Denzir was >1.3-mm Denzir (p<0.001). Sandblasting with 0.2 MPa reduced the BFS of the ZirPlus and Denzir discs (p<0.01), whereas sandblasting with 0.6 MPa increased the BFS of the 0.4-mm Denzir (p<0.001) and reduced the BFS of the 0.4-mm ZirPlus (p <0.05). Heat treatment significantly reduced the BFS of all the groups except for the 0.6 MPa sandblasted 0.4-mm ZirPlus. Autoclaving reduced the BFS of the as-delivered ZirPlus and Denzir specimens (p<0.001), whereas autoclaving the 0.6 MPa sandblasted and heat-treated specimens had no effect (p>0.05) on the BFS. The 0.6 MPa sandblasted, heat-treated, and autoclaved 0.4-mm Denzir exhibited higher BFS than the 0.6 MPa sandblasted, heat-treated, and autoclaved 0.4-mm ZirPlus (p <0.05). Conclusions: Thickness and surface treatment of Y-TZP-based ceramics should be considered since those factors could influence the BFS of the material.