Color difference thresholds in dental ceramics

The objective of the study was to determine the perceptibility and acceptability thresholds for dental ceramics using CIEDE2000 (ΔE(00)) and CIELAB (ΔE(ab)(*)) color difference formulas and a novel TSK Fuzzy Approximation.

A 13-observer panel performed independent observations of perceptibility and acceptability judgments on 105 pairs of ceramic discs (14mm in diameter and 3mm thick). Color differences of the disc pairs were calculated using both color difference formulas (ΔE(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).

With the S-shaped fitting procedure, a 50:50% acceptability threshold was found to be ΔE(00)=2.25 (r(2)=0.88) and ΔE(ab)(*)=3.46 (r(2)=0.85). Corresponding values with a TSK Fuzzy Approximation were ΔE(00)=2.23 (r(2)=0.89) and ΔE(ab)(*)=3.48 (r(2)=0.86). The perceptibility thresholds for fitted S-shape curves were ΔE(00)=1.30 (r(2)=0.74) and ΔE(ab)(*)=1.80 (r(2)=0.70) and ΔE(00)=1.25 (r(2)=0.75), and ΔE(ab)(*)=1.74 (r(2)=0.71) for the TSK Fuzzy Approximation. The ΔL', ΔC', ΔH' values corresponding to a 50% acceptability threshold were ΔL'=2.44, ΔC'=3.15 and ΔH'=3.24 respectively.

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.