Applicability of CIELAB/CIEDE2000 formula in visual color assessments of metal ceramic restorations

ObjectivesTo investigate the applicability of color-difference formula (CIELAB or CIEDE2000) in visual color assessments of metal-ceramic specimens in small color-difference ranges.MethodsMetal-ceramic specimens using mixture of gradient ratio porcelain powders were fabricated to create a color pool. Color differences of specimen pairs were calculated using the CIELAB (ΔEab∗) and CIEDE2000 (ΔE00). A questionnaire, composed of 1 target and 3 enactment specimens, was designed. For formula-determination, the enactment specimen with the minimum ΔE to the target specimen was registered as FS. For visual-assessment, twenty participants were asked to finish the questionnaire by choosing the most color-matched enactment specimen to the target. The percentage of the FS been selected (PFS) was calculated, which was used to represent the consistence of formula-determination and visual-assessment. Binomial Tests were used to compare the differences between PFS values and 33% (the randomized probability of the FS been selected was one out of three, approximate 33%). Regression analysis was used to determine the correlation between ΔEab∗ and ΔE00 values.ResultsA linear regression equation was drawn as ΔE00=−0.049+0.619×ΔEab∗. There were no significant differences between PFS values and 33% within the range of ΔEab∗<2.0, whereas PFS values were significantly higher than 33% when ΔEab∗>2.0 (P < 0.001). There was a tendency of selecting the enactment specimens with lower L* values and higher b* or C  ′ values, within the range of 1.0<ΔEab∗<2.0.ConclusionsCIE color-difference formulas were not applicable for visual color assessments of metal-ceramic specimens within the color-difference range of ΔEab∗<2.0.