Effect of hydrothermal aging on the optical properties of monolithic zirconia ceramics

Background/Purpose: Monolithic zirconia which have good optical properties and excellent mechanical properties such as flexural strength and fracture resistance. This study aimed to investigate the effect of hydrothermal aging on the optical properties of the monolithic zirconia. Materials and methods: In this in vitro study, some groups of all-ceramic restorations were examined, of which monolithic zirconia with high translucency was used as the restorative material and three materials, grade 5 titanium and white and yellow zirconia, as substructure materials. Color standard characteristics, l, a and b values, were measured and recorded by a digital spectrophotometer before and after the aging process. Then, the mean values of data were compared by variance analysis. Results: The statistical results show that the difference in mean values of color changes (.E) between the titanium group and yellow zirconia group was statistically significant. However, no significant difference was observed between titanium and white zirconia groups and between white zirconia and yellow zirconia groups. In all the groups, the differences in the mean.E in various thicknesses were significant. The differences between the mean l, a, and b indices were significant in all the groups before and after the aging process. Conclusion: The color changes associated with the aging process were higher in the yellow zirconia group than in the other two groups. The l and.E indices decreased, and the a and b values increased due to the aging process. Restorations with the thickness of 1.5-mm and above exhibited greater color stability after aging.