Color difference thresholds in dental ceramics

Objectives: The objective of the study was to determine the perceptibility and acceptability thresholds for dental ceramics using CIEDE2000 (Delta E-00) and CIELAB (Delta E*(ab)) color difference formulas and a novel TSK Fuzzy Approximation. Methods: A 13-observer panel performed independent observations of perceptibility and acceptability judgments on 105 pairs of ceramic discs (14 mm in diameter and 3mm thick). Color differences of the disc pairs were calculated using both color difference formulas (Delta E-00 ranged from 0.10 to 9.91). Two fitting procedures were used: S-shaped curve and TSK Fuzzy Approximation. For both procedures, from the resultant fitting curves, the 95% confidence intervals were estimated and the 50:50% thresholds were calculated (50% positive and 50% negative answers). Results: With the S-shaped fitting procedure, a 50: 50% acceptability threshold was found to be Delta E-00 = 2.25 (r(2) = 0.88) and Delta E*(ab) 3.46 (r(2) = 0.85). Corresponding values with a TSK Fuzzy Approximation were Delta E-00 = 2.23 (r(2) = 0.89) and Delta E*(ab) 3.48 (r(2) = 0.86). The perceptibility thresholds for fitted S-shape curves were Delta E-00 = 1.30 (r(2) = 0.74) and Delta E*(ab) 1: 80 (r(2) = 0.70) and Delta E-00 = 1.25 (r(2) = 0.75), and Delta E*(ab) 1.74 (r(2) = 0.71) for the TSK Fuzzy Approximation. The Delta L', Delta C', Delta H' values corresponding to a 50% acceptability threshold were Delta L' = 2.44, Delta C' = 3.15 and Delta H' = 3.24 respectively. Conclusions: The CIEDE2000 color difference formula provided a better fit than CIELAB formula in the evaluation of color difference thresholds of dental ceramics. There was a statistically significant difference between perceptibility and acceptability thresholds for dental ceramics. The TSK Fuzzy Approximation has been proved to be a reliable alternative approach for the color threshold calculation procedure. (C) 2010 Elsevier Ltd. All rights reserved.