Effect of thickness of monolithic zirconia ceramic on final color

Statement of problem. Achieving excellent esthetics with monolithic zirconia restorations is challenging, and the impact of monolithic zirconia thickness on the final color is unclear. Purpose. The purpose of this in vitro study was to assess the effect of thickness of monolithic zirconia ceramic on its final color and to define the minimum thickness needed to gain an acceptable final color. Material and methods. Sixty monolithic zirconia disk specimens with a 10-mm diameter and 3 different thicknesses (0.7, 0.9, and 1.1 mm) were fabricated from 2 zirconia brands. The specimens were divided into 6 groups of 10 based on the thickness and brand. All the specimens were colored with an A2 shade liquid. The specimens were placed on an A4 shade substrate, and their CIELab values were measured with a spectrophotometer. Delta E values were calculated to determine color differences between the specimens and the A2 VITA classical shade tab. The Delta E values were compared with an acceptability threshold (Delta E=3.3). Two-way ANOVA, the Bonferroni test, and 1-sample t test were used to analyze data (alpha=.05). Results. Mean Delta E values ranged between 2.4 and 4.1. The zirconia thickness affected the Delta E (P<.001); however, the zirconia brand did not affect the Delta E (P=.059). The mean Delta E values for the zirconia thickness of 0.7 mm for both brands were more than the threshold (P<.05). Conclusions. The thickness of monolithic zirconia ceramic affected its final color. The minimum thickness of a monolithic zirconia ceramic should be 0.9 mm to gain the acceptable final color.