An In Vitro Investigation of Veneered Zirconia-Based Restorations Shade Reproducibility

Purpose: To examine the effects of the veneering technique on the shade reproducibility of zirconia-based crowns. Materials and Methods: An artificial tooth was prepared with a 1.2 mm heavy chamfer finish line and 8 degrees taper. The prepared tooth was scanned using CAD/CAM technology to fabricate 45 cobalt chromium (CoCr) testing dies. One CoCr die was scanned, and 45 zirconia copings were milled and devided according to the veneering technique into 3 groups of 15 specimens each: layering veneering (LV) using Vita Vm9, overpressing veneering (OV) using Vita Pm9, and digital veneering (DV) using Vita Triluxe forte. All veneering layers had the same shade (A2). The specimens were cemented onto the testing dies using glass inomer cement. A spectrophotometer was used to measure the shade coordinates (L, C, h, a, b) for a Vita A2 shade tab and for each specimen. Both the CIE Lab (Delta E-ab) and the CIE DE2000 (Delta E-00) color difference formulas were applied to compare the shade tab and the study groups. One-way ANOVA and multiple comparison Bonferroni tests were applied for statistical analysis of the results. Results: Means and standard deviations (SDs) of E-ab were 2.3 1.3 for LV, 3.5 +/- 0.8 for OV, and 4.0 +/- 0.7 for DV. Means and SDs of Delta E-00 were 1.4 +/- 0.8 for LV, 2.1 +/- 0.5 for OV, and 3.1 +/- 0.4 for DV. Delta E-ab of LV group was significantly lower (p < 0.05) than both OV and DV groups, whereas the difference in Delta E-ab between OV and DV groups was not significant (p = 0.39). The differences in Delta E-00 between all groups were significant (p < 0.05). Conclusions: LV group was superior to other groups in terms of shade reproducibility. The E-ab and the Delta E-00 values of LV and OV groups were within clinically acceptable ranges; however, the Delta E-ab and the Delta E-00 values of group DV were beyond the clinically acceptable ranges. The Delta E-00 formula demonstrated a statistically significant difference between OV and the DV groups, while the E-ab formula did not. The zirconia veneering technique had a significant influence on the shade reproducibility of zirconia-based crowns.