Color difference thresholds in dental ceramics

Abstract

Objectives The objective of the study was to determine the perceptibility and acceptability thresholds for dental ceramics using CIEDE2000 (Δ E 00) and CIELAB ( Δ 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 3 mm thick). Color differences of the disc pairs were calculated using both color difference formulas (Δ 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 Δ E 00 = 2.25 ( r 2 = 0.88) and Δ E ab * = 3.46 ( r 2 = 0.85). Corresponding values with a TSK Fuzzy Approximation were Δ E 00 = 2.23 ( r 2 = 0.89) and Δ E ab * = 3.48 ( r 2 = 0.86). The perceptibility thresholds for fitted S-shape curves were Δ E 00 = 1.30 ( r 2 = 0.74) and Δ E ab * = 1.80 ( r 2 = 0.70) and Δ E 00 = 1.25 ( r 2 = 0.75), and Δ E ab * = 1.74 ( r 2 = 0.71) for the TSK Fuzzy Approximation. The Δ L′, Δ C′, Δ H′ values corresponding to a 50% acceptability threshold were Δ L′ = 2.44, Δ C′ = 3.15 and Δ 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.