Influence of Repeated Firings on the Optical Properties of Zirconia Ceramic Core with Different Thicknesses of Veneering Ceramic: An in vitro study

Abstract

Statement of the problem: The optical properties of the zirconia based ceramic restoration may be affected by its fabrication protocol and the veneer thickness.Objectives: This study was aimed to investigate the effect of repeated firings and veneer thickness on the final color and translucency of zirconia based ceramic restorations.Materials and methods: 80 disc-shaped zirconia cores (diameter: 10×1 mm) were constructed then divided based on the veneer thickness into 2 main groups (A) and (B) (n=40) with 0.5 mm and 1.00 mm veneer thicknesses, respectively. According to the number of firing cycles (1, 3, 5, and 7), each main group was further subdivided into four subgroups (n=10). A spectrophotometer was utilized to measure the color and translucency after consecutive firings then used to measure them after artificial thermomechanical aging. Data analysis was performed by One-way ANOVA analysis, Paired t-test and Tukey post hoc test.Results: All measured L*, a* and b* and ΔΕ values showed statistical significant differences after repeated firing cycles. Increasing the veneer thickness for all tested subgroups resulted in statistically significant increasing in mean values of L*, a* and b*. Increasing the number of firing cycles significantly increased the TP, while increasing the zirconia veneer thickness significantly decreased them. Following fatigue aging, statistically significant differences were noticed for all color coordinates with all tested subgroups with increased TP.Conclusions: Both firing cycles and veneer thickness had an impact on optical properties of zirconia-based ceramic restorations. Color parameters and translucency were influenced by artificial fatigue aging.