The effect of different surface finishing procedures on the color and translucency of monolithic zirconia after low-temperature degradation

Aim: The aim of this thesis is to investigate in vitro the effects of different surface finishing processes and hydrothermal aging on the color and translucency of two different monolithic zirconia materials. Materials and Methods: In the study, samples 4Y-ZTP and 5Y-TZP (Vita YZ ST and Vita YZ XT, Vita Zahnfabrik, Germany) including 2 different CAD/CAM zirconia materials were used. 60 samples of each materials, 120 samples in total were prepared with final dimensions of 15 mm in diameter and 1.2 mm in thickness . Following the sintering process (2 hours at 1450°C) in accordance with the manufacturer's instructions, each material group was divided into three subgroups based on the surface treatment applied. The groups underwent polishing with a zirconia polishing kit, glazing, and a combination of polishing + glazing. Half of the samples were subjected to hydrothermal aging at 134°C and 0.2 MPa pressure for 10 hours (n=10). Color measurements were recorded using the CIEDE2000 formula with a white background, and translucency measurements were taken against both white and black backgrounds. The differences in color and translucency were calculated. Data were analyzed using Minitab v14 and R software. Three-way ANOVA and Tukey's multiple comparison tests were conducted, and for data not following a normal distribution, Robust ANOVA was performed using the WRS2 package. Multiple comparisons were evaluated using the Bonferroni test (p<0.05). Results: The statistical analysis revealed that surface finishing processes and hydrothermal aging significantly affected the color values of monolithic zirconia materials (p<0.05). While the type of zirconia caused a significant difference in translucency values (p<0.05), surface finishing processes and hydrothermal aging had no significant effect on translucency values (p>0.05). The color stability in groups with glaze application was found to be below the clinically perceptible level (ΔE<0.8), whereas in groups subjected to polishing and polishing followed by glaze application, the ΔE values were found to be between the clinically acceptable and perceptible levels (0.8<ΔE<1.8). All color and translucency changes remained within clinically acceptable limits. Conclusion: In this study, it was determined that samples subjected to glazing after hydrothermal aging exhibited better color and translucency properties compared to those polished only. Therefore, it was concluded that glazing should be prioritized in the finishing processes of monolithic zirconia restorations. However, since the color and translucency changes in samples treated with polishing and polishing + glazing remained below clinically detectable levels, these methods can also be considered viable options Keywords: Monolithic Zirconia, Surface Finishing Process, Color Differences, Tranc Slusencty, Hydrotermal Aging.