Effect of Varying Thickness and Number of Coloring Liquid Applications on the Color of Anatomic Contour Monolithic Zirconia Ceramics

STATEMENT OF THE PROBLEM: There is not enough information available about the effect of thickness reduction and the coloring method on the color of new monolithic zirconia ceramic system. PURPOSE: This study aimed to evaluate the effect of varying thickness reductions and number of coloring liquid applications on the final color of anatomic contour monolithic zirconia ceramics. MATERIALS AND METHOD: In this experimental in-vitro study, 48 disk-shaped monolithic zirconia specimens (10×2mm) were divided into three groups (Group I to III) according to the number of A2-coloring liquid applications (n=16). Each group was then divided into 4 subgroups (n=4) by reducing the thickness of 2 to 0.5 mm in increments of 0.5 mm on the colored surface. Color measurement was done through CIELab (l*, a*, b*) on a reflection spectrophotometer on five different areas of each specimen. Color differences (∆E) were calculated. Data were analyzed by using two-way ANOVA and Tukey’s HSD test (α=0.05). RESULTS: The number of coloring liquid applications and reducing the thickness of monolithic zirconia disks had significant effects on CIE L* a* and b* values. The CIEL*, a* and b* values increased as the thickness decreased (p< 0.05), whereas, increasing the number of coloring liquid applications resulted in decreased CIE L* value and increased CIE a* and b* values (p< 0.05). CONCLUSION: Decreasing the thickness of monolithic zirconia increases the lightness and reddish, yellowish appearance. Meanwhile, increasing the number of coloring liquid applications reduces the lightness and makes it seem more reddish and yellowish.