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

To investigate the applicability of color-difference formula (CIELAB or CIEDE2000) in visual color assessments of metal-ceramic specimens in small color-difference ranges.

Metal-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 (ΔE(ab)(∗)) and CIEDE2000 (ΔE(00)). 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 (P(FS)) was calculated, which was used to represent the consistence of formula-determination and visual-assessment. Binomial Tests were used to compare the differences between P(FS) 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 ΔE(ab)(∗) and ΔE(00) values.

A linear regression equation was drawn as ΔE(00)=-0.049+0.619×ΔE(ab)(∗). There were no significant differences between P(FS) values and 33% within the range of ΔE(ab)(∗)<2.0, whereas P(FS) values were significantly higher than 33% when ΔE(ab)(∗)>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<ΔE(ab)(∗)<2.0.

CIE color-difference formulas were not applicable for visual color assessments of metal-ceramic specimens within the color-difference range of ΔE(ab)(∗)<2.0.