Illuminant Effect on the Coverage Error of a Gingival Shade-Guide

Objectives: To evaluate the coverage error (CE) of a gingiva-colored dental resin-composite shade-guide relative to the colors of attached gingiva under CIE Illuminants A and D65.
Methods: The spectral reflectance (SR) values of shade guides of a gingiva-colored resin-composite (Amaris Gingiva) were measured at 3 different locations without a backing using a spectroradiometer and an external light source at wavelengths from 380 nm to 780 nm at 2-nm intervals. All SR measurements were made using 0-degree observer and 45-degree illumination with target size 1.1 mm in diameter. The attached gingiva (AG) of 120 subjects was measured with the same protocol (Gozalo-Diaz DJ et al. J Prosthet Dent 2007;97:45-53.). The CIEDE2000 color difference for 120 subjects’ gingiva to the closest match in color to the shade guide was determined separately for CIE Illuminants A and D65. CE was calculated as the averages of these color differences. These color differences were analyzed by a repeated measures ANOVA using the maximum likelihood estimation method and the Satterthwaite degrees of freedom method.
Results: The CEs were found to be 4.0 for CIE Illuminant D65 and 5.8 for CIE Illuminant A, and these CEs were found to be statistically significantly different (P<0.001).
Conclusions: There was a metameric effect between gingiva-colored resin-composite shade-tab and attached gingiva. The CEs were greater than the perceptibility limit (1.275) and the acceptability limit (2.24) for CIEDE2000 for the illuminants studied. This confirmed the difficulty in gingiva shade matching and the need to match shades under the light corresponding to that of daily use.