Aging Effect on Flexural Strenght of Zirconia in Different Thicknesses

Objectives: The purpose of this study was to investigate the aging characteristics of three yttria-stabilized tetragonal zirconia polycrystalline materials (Prettau, Supra, Lava) and effect of aging on flexural strenght.
Methods: Total of 120 bars ( 25 mm × 4 mm ) were obtained from three presintered zirconia-based materials (Prettau, Supra, Lava) in different thicknesses (0.5 mm, 1 mm, 1.5 mm, 2 mm). Specimens were cut and ground from blocks and sintered according to manufacturers specifications. Control specimens for each brand left in distilled water at 37°C for 5 h.Experimental specimens were artificially aged at standard autoclave sterilization conditions, 134°C at 0.2 MPa for 5h and standard industrial ceramic aging conditions, the specimens were left in 4% asetic asid at 80°C for 168.Tetraragonal to monoclinic transformation was measured by using X-ray diffraction for all groups. Flexural strength was measured in biaxial flexural strenght test for all groups.Datas were analyzed using one-way ANOVA and Kruskall Wallis follewed by Tukey HSD and Mann Whitmey U test (α=.05).
Results: Corresponding to the XRD results; relative amount of the monoclinic phase content showed diversity among the groups due to aging. The lowest biaxial flexural strength mean was recorded in Supra.
Conclusions: Hydrothermal aging of Y-TZP can cause significant transformation from tetragonal to monoclinic crystal structure, which results in a statistically significant decrease in the flexural strength of thin bars. Long term in vivo studies are insisted to evaluate whether the results presented are transmissible to the clinical situation.