Use of a porcelain color discrimination test to evaluate color difference formulas

Limited studies have indicated that an alternative small color difference formula would be more appropriate for use in dentistry.

The purposes of this study were to determine which color difference formula provides a superior degree of fit for judgments of perceptibility and acceptability and to determine if different groups of evaluators have different levels of perceptibility and acceptability for each color difference formula.

Each observer from 4 groups (4 dentists, 4 dental assistants, 4 technicians, and 4 patients)made independent observations of perceptibility and acceptability judgments on pairs of opaque porcelain (VitaOmega 900) disks (14 mm in diameter by 3 mm thick). Color differences of the pairs were calculated using DeltaE*(ab), DeltaE(CMC)(l:c), and DeltaE(2000) color difference formulas, and the observer judgments were regressed to each color difference in dependently for perceptibility and acceptability. The area under the receiver operator curves was calculated and ranked, and the optimal factor for the CMC (Colour Measurement Committee, Society of Dyers and Colourists, Great Britain) color difference formula was chosen. A repeated measures maximum likelihood ANOVA (alpha=.05) was applied to determine statistical significance of fit among the observer groups, and the various color difference formulas for both perceptibility and acceptability. Tukey-Kramer Adjustment (alpha=.05) was used as a post hoc test.

A difference in the degree of fit of the judgments of color differences was found for the 3 formulas (P=.001)and the 2 judgment types (P<.001) studied, with no significant interaction (P=.979). The Tukey-Kramer test identified a lower degree of fit for the DeltaE*(ab) formula compared to DeltaE(CMC)(2:3) and DeltaE(2000) formulas. No significant difference was found in the mean judgment levels among the observer groups (P=.474) studied, nor within any interaction (P>.404).

DeltaE(2000) and DeltaE(CMC)(2:3) color difference formulas provide a better fit to the calculated color differences,therefore providing better indicators of human perceptibility and acceptability of color differences between tooth colors.