59 - Effect of Aging Treatment on Fracture Properties of Multilayer Zirconia.

Multilayer zirconia can improve the color and translucency of traditional zirconia. However, the difference in mechanical property and chemical composition among the layers of multilayer zirconia may affect the structural integrity and even the fracture properties of zirconia prostheses. Currently, literature on the fracture performance of multilayer zirconia is very limited. The objective of the study was to investigate the effect of aging treatment on the fracture properties of multilayer zirconia by using four-point bending and biaxial bending tests according to ISO 6872 specifications. Three kinds, including 3, 4, and 5 mol % of yittria, of monolayer zirconia and two kinds, including color gradient and translucency gradient, of multilayer zirconia were used in this study. The test samples were divided into two shapes: strip samples for the four-point bending test and disc samples for the biaxial bending tests. All samples were divided into three groups, including control group, 5-hour aging group, and 20-hour aging group. The aging treatment at 134°C and 0.2 MPa for 5 h was referred to ISO 13356. The four-point bending, and biaxial bending strengths of each group were analyzed statistically by one-way ANOVA. Weibull analysis was performed to calculate the Weibull modulus. Fracture surface morphology and crystalline structure were also analyzed, respectively, by using scanning electron microscope and X-ray diffractometer. The four-point bending strength of multilayer zirconia before and after the aging treatment was significantly lower than that of monolayer zirconia. The color gradient multilayer zirconia did not have a significant difference in bending strength after aging treatment; the translucency gradient multilayer zirconia had an increase in four-point bending strength after aging treatment, but a decrease in biaxial bending strength (Fig. 1). The Weibull modulus of multilayer zirconia was lower than that of monolayer zirconia; multilayer zirconia had more defects than monolayer zirconia, leading to its lower structural stability. The short (5 h) aging treatment did not significantly affect the crystalline structure of the test samples, but when the aging time increased to 20 h, a significant change in the crystalline structure and a decrease in fracture property were obtained. The aging treatment may affect the fracture properties of multilayer zirconia, depending on the aging time and the type (color gradient or translucency gradient) of multilayer zirconia. [Display omitted] [ABSTRACT FROM AUTHOR]