The Optical Effect of Zirconia Background, Ceramic Thickness, and Cement on All-Ceramic Material

Hypothesis: The color differences of all-ceramic restoration material would be affected relative to different zirconia abutment shades, all-ceramic thicknesses, and resin cement. Objective: To investigate the optical influence of various all-ceramic restoration material thicknesses, zirconia abutment shades and resin cement on the optical resultant color of all-ceramic restoration using a dental spectrophotometer. Methods: Heat-pressed lithium disilicate ceramic disks (IPS E.max) were fabricated in 4 different thicknesses, ranging from 0.5 to 2.0mm, and zirconia abutment disks (Atlantis) with 3.0mm thickness were fabricated in 3 different shades including the original white shade and 2 newly introduced dentine-like shades. The all-ceramic disks were placed over zirconia abutment disks with glycerin. Color measurements were made using a dental spectrophotometer (Crystaleye) for all the crown-abutment combinations with varying ceramic thickness and zirconia shades. For the evaluation of the optical effect of cement, all-ceramic disks were luted to the lightly shaded zirconia abutment disks using tooth-colored resin cement (PANAVIA) at 0.1mm film thickness, and color measurements were made with 4 different ceramic thicknesses. Three measurements were taken each time, and color differences, ∆E, ∆L*, ∆a*, and ∆b* values, were calculated with the white zirconia abutment as a control. The mean color differences were analyzed using two-way ANOVA and Tukey post hoc test (p ≤ 0.05). Results: The underlying zirconia abutment shade, ceramic thickness, and resin cement all influence the final optical color of all-ceramic restoration material (p<0.05). The zirconia abutment with the darker shade, thinner all-ceramic material, and the presence of tooth-colored resin cement resulted in larger ∆E values. The color differences with thinner all-ceramic materials were found to be well beyond the clinically acceptable threshold (∆E > 3.7), and the color differences diminished with increasing overlaying ceramic thickness. Conclusion: Careful selection of the zirconia abutment shade and luting agent with the consideration of ceramic thickness is important in obtaining optimal esthetics.