Influence of illuminants on the color distribution of shade guides

Abstract

Although a shade tab in a shade guide is matched to a natural tooth in the order of value, hue, and chroma, there are limited data on the color distribution of currently available shade guides sorted by these 3 parameters. Furthermore, spectrophotometric color measurements of shade tabs differ depending on the standard illuminant employed. The purpose of this study was to determine the color distributions of 2 shade guides in value (CIE L( *)), chroma (C( *)(ab)) and hue angle (h(o)) scale relative to the standard illuminants D(65), A, and F2. Color of shade tabs (n=36) from 2 shade guides (Vita Lumin and Chromascop) were measured, and the distributions for CIE L( *), C( *)(ab) and h(o) values were compared. Color differences of shade tabs depending on the illuminant were calculated. The distributions of the ratios of CIE L( *) and C( *)(ab) values of each shade tab compared with the lowest value tab or the lowest chroma tab were determined. The data for the value, chroma, and hue angle within each shade guide were analyzed with a 2-way ANOVA with the factors of shade designation and type of illuminant (alpha=.05). Color difference caused by change of illuminant was analyzed with a 2-way ANOVA with the factors of shade designation and pair of illuminants compared (alpha=.05). The Scheffe multiple comparison test was performed as a post hoc test. CIE L( *), C( *)(ab) and h(o) values were influenced by shade designation and type of illuminant in both shade guides. Color difference caused by change of the illuminant was influenced by the shade designation and pair of illuminants compared. The order of mean color differences of 16 Vita Lumin shade tabs by pairs of illuminants compared was as follows: DeltaE( *)(ab) (D(65)/F2) = 1.63 <DeltaE( *)(ab) (D(65)/A) = 2.22 <DeltaE( *)(ab) (A/F2) = 2.46 (P<.05). The order of mean color differences of 20 Chromascop shade tabs was as follows: DeltaE( *)(ab) (D(65)/F2) = 2.45 <DeltaE( *)(ab) (D(65)/A) = 2.71 <DeltaE( *)(ab) (A/F2) = 3.14 (P<.05). The distributions of value and chroma in both shade guides were arbitrary. Color distribution of 2 shade guides varied by the illuminant, and the range of color difference for shade tabs by the illuminant was 0.80 to 4.82, which may be clinically unacceptable (DeltaE( *)(ab) > 3.7). Color distribution of 2 shade guides by the value and chroma was not logical.