Effect of Repeated Firings and Thickness on Optical Properties of Variable Preshaded and Shaded Novel Translucent Zirconia Blocks

Abstract

Objective. The purpose of this study was to examine the optical properties of translucent zirconia with different thickness during multiple firings. Materials and Methods. Three different types of translucent zirconia (Vita YZ HT (HT), Vita YZ ST (ST), Vita YZ XT (XT)) with thickness of 0.5, 1, and 1.5 mm were used in the study. 180 disk-shaped specimens ( $n=10$ ) were prepared from preshaded and nonshaded blocks. The coloring liquid (A2, Vita Shade Liquid) was applied with a synthetic nylon brush in the nonshaded group. Then, the specimens were then subjected to 1, 3, and 5 firing times. After consecutive firings, color differences ( $\Delta E$ ) and translucency parameter ( $\text{TP}$ ) were measured. Statistical analysis was carried out by using repeated measure ANOVA followed by Tukey test. Results. ANOVA analysis reveals that $\text{TP}$ and $\Delta E$ were significantly affected by the repeated firings. The highest $\text{TP}$ was seen in 0.5 mm XT specimen. For all specimens, $\text{TP}$ decreases from 1st to 3rd firing cycles, despite $\text{TP}$ increases from 3rd to 5th firing cycles. Although there is a significant change in $\text{TP}$ values in 0.5 mm thickness, there is no significant change between firing cycles for 1 and 1.5 mm thickness specimens. The highest $\Delta E$ value was observed for shaded specimens between 1st and 5th firings. $\Delta E$ values were not significantly different between 1 and 3 firings. Conclusions. Changes in thickness and repeated firings of zirconia specimens affected final color and translucency of zirconia specimens. HT blocks are more affected by consecutive firings than ST and XT blocks. $\Delta E$ increased as the thicknesses decreased for both types of translucent zirconia specimens tested.