Effect of the amount of thickness reduction on color and translucency of dental monolithic zirconia ceramics

PURPOSE: This study investigated the effect of amount of thickness reduction on color and translucency of dental monolithic zirconia ceramics. MATERIALS AND METHODS: One-hundred sixty-five monolithic zirconia specimens (16.3 mm × 16.3 mm × 2.0 mm) were divided into 5 groups (Group I to V) according to the number of A2-coloring liquid applications. Each group was then divided into 11 subgroups by reducing the thickness up to 1.0 mm in 0.1-mm increments (Subgroup 0 to 10, n=3). Colors and spectral distributions were measured according to CIELAB on a reflection spectrophotometer. All measurements were performed on five different areas of each specimen. Color difference (ΔE(*)(ab)) and translucency parameter (TP) were calculated. Data were analyzed using one-way ANOVA and multiple comparison Scheffé test (α=.05). RESULTS: There were significant differences in CIE L(*) between Subgroup 0 and other subgroups in all groups. CIE a(*) increased (0.52<R(2)<0.73), while CIE b(*) decreased (0.00<R(2)<0.74) in all groups with increasing thickness reduction. Perceptible color differences (ΔE(*) (ab)>3.7) were obtained between Subgroup 0 and other subgroups. TP values generally increased as the thickness reduction increased in all groups (R(2)>0.89, P<.001). CONCLUSION: Increasing thickness reduction reduces lightness and increases a reddish, bluish appearance, and translucency of monolithic zirconia ceramics.