The Effect of Different Foundation Materials on the Color of Monolithic Zirconia at Different Thicknesses

Statement of the Problem: Monolithic zirconia restoration has been introduced to overcome the porcelain chipping. Different factors can affect the color of monolithic zirconia, so achiev-ing the desired color in the restorations is considered as a challenge. Purpose: The purpose of this in vitro study was to determine the effect of different founda-tion materials on the color of monolithic zirconia at different thicknesses. Materials and Method: In this experimental study, thirty ceramic disks in three thicknesses (i.e. 0.6mm, 1.1mm and 1.5mm) were fabricated from high translucency shade A_2 monolithic zirconia block. Disk shaped foundation materials were fabricated from nickel chromium alloy (Ni-Cr), non- precious gold alloy (NPG), zirconia, and shade A2 composite resin. The color was measured by a spectrophotometer. The color differences (ΔE) in the control and the test groups were calculated. The data were analyzed using two way ANOVA and compared with the post-hoc Tukey test (a=0.05). Results: Ceramic thickness and foundation materials had a significant effect on the mean values of ΔE of monolithic zirconia ceramics (p= 0.001). The highest amount of ΔE value was observed in NPG, while Ni-Cr resulted in the lowest ΔE. Unacceptable results (ΔE 2.25) were observed for monolithic zirconia ceramics on NPG foundation material with a thick- nesses of 0.6 and 1.1mm. The mean L* values of all foundation materials were higher than those of the control group except for Ni-Cr. The highest a* was seen in NPG and the mean b* values of all tested foundation materials were higher than those of the control group except for Ni-Cr. Conclusion: Increasing the thickness of monolithic zirconia decreased the color mismatch. High translucent monolithic zirconia could mask the color of Ni-Cr and zirconia in all three thicknesses (ΔE˂2.25), while it could not mask the color of NPG under thickness of 1.5mm.