Influence of enamel layer thickness on the shade of the double layer build-up technique

Abstract

Objective: The purpose of this in-Vitro study was to evaluate the color-matching ability of two resin-based composite (RBC) Systems; Gaenial Sculpt Universal (GC America, USA) & Transcend Universal (Ultradent Products Inc., USA), using three different enamel layer thicknesses (0.5 mm, 0.7 mm & 1.0 mm) Relative to the VITA Classical A2 shade using the CIE color system with DE00 Materials and Methods: Sixty specimens were fabricated using two resin composite systems and three enamel thicknesses (0.5 mm, 0.7 mm, and 1.0 mm; n = 10 per group). Three-dimensional printed molds were generated from a scanned VITA Classical A2 shade tab. Color measurements were obtained using a spectrophotometer under standardized conditions. CIEDE2000 (ΔE00) was used to evaluate color differences relative to the VITA Classical A2 reference shade, whereas ΔEab and individual color coordinates (ΔL, Δa*, and Δb*) were used to compare the six experimental groups. Statistical analyses included descriptive statistics, normality testing, two-way ANOVA, one-way ANOVA, multivariate analysis of variance (MANOVA), and Tukey post-hoc comparisons. The level of significance was set at α = 0.05. Results: For ΔE00, two-way ANOVA demonstrated no statistically significant effect of composite system (p = 0.076), enamel thickness (p = 0.131), or their interaction (p = 0.509). Descriptively, lower mean ΔE00 values were observed in the 1.0 mm enamel thickness groups; however, these differences were not statistically significant. Analysis of ΔEab revealed significant differences among the six experimental groups (p = 0.012), with Tukey post-hoc testing identifying a significant difference between G-aenial Sculpt Universal 1.0 mm and Transcend Universal 0.5 mm. Multivariate analysis of the individual color coordinates demonstrated significant effects of both enamel thickness and composite system on ΔL, Δa*, and Δb*. Post-hoc comparisons revealed significant differences between 0.7 mm and 1.0 mm enamel thicknesses for ΔL*, whereas Δa* and Δb* demonstrated significant differences among all enamel thickness groups. Significant differences were also observed between the two composite systems for all three color coordinates. Conclusion: Within the limitations of this in-vitro study, neither enamel thickness nor composite system significantly influenced color matching to the VITA Classical A2 reference shade when evaluated using the CIEDE2000 color difference metric (ΔE00). No tested combination achieved a close color match to the VITA Classical A2 reference shade. However, significant differences were observed among the experimental groups when assessed using ΔEab and the individual CIELAB color coordinates. Both enamel thickness and composite system significantly influenced ΔL, Δa*, and Δb*, with changes in the yellow-blue coordinate (Δb*) contributing substantially to the observed color differences. Although thicker enamel layers demonstrated descriptively lower ΔE00 values, these differences were not statistically significant. These findings suggest that 30 material-specific optical characteristics and color-coordinate changes may have a greater influence on final color reproduction than enamel thickness alone. Keywords: CIEDE2000; color difference; spectrophotometry; resin-based composites; translucency; dental esthetics; VITA Classical A2; layered restorations.