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

Objectives: To investigate the applicability of color-difference formula (CIELAB or CIEDE2000) in visual color assessments of metal-ceramic specimens in small color-difference ranges. Methods: 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 (Delta E-ab*) and CIEDE2000 (Delta E-00). A questionnaire, composed of 1 target and 3 enactment specimens, was designed. For formula-determination, the enactment specimen with the minimum Delta E 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 Delta E-ab* and Delta E-00 values. Results: A linear regression equation was drawn as Delta E-00 = -0.049 + 0.619 x Delta E-ab*. There were no significant differences between P-FS values and 33% within the range of Delta E-ab* < 2.0, whereas P-FS values were significantly higher than 33% when Delta E-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 < Delta E-ab* < 2.0. Conclusions: CIE color-difference formulas were not applicable for visual color assessments of metal-ceramic specimens within the color-difference range of Delta E-ab* < 2.0. (C) 2012 Elsevier Ltd. All rights reserved.