Multicenter study on visual color difference thresholds. A secondary analysis of light, medium, and dark tooth-colored specimens.

PURPOSE: This secondary analysis further analyzed variations in the 50:50% perceptibility and acceptability thresholds (PT and AT, respectively) pertaining to light, medium, and dark tooth-colored specimen sets. METHODS: Primary raw data from the original study was retrieved. Visual thresholds (Perceptibility - PT and Acceptability - AT) were analyzed among the three specimen sets - light, medium, and dark. The Wilcoxon signed-rank test was used for paired specimens, and the Wilcoxon rank-sum nonparametric test was used for independent specimens (α= 0.001). RESULTS: The 50:50% CIEDE2000 PT and AT values were significantly higher for the light-colored specimen set when compared with the medium and dark-colored specimens: 1.2, 0.7, 0.6, respectively (PT) and 2.2, 16, 14 (AT), respectively (P< 0.001). Independent of the observer group, the highest PT and AT values were always found for the light-colored specimen sets (P< 0.001). Dental laboratory technicians had the lowest visual thresholds, but not significantly different from the other observer groups studied (P> 0.001). Similarly, all research sites had statistically higher visual thresholds for the light-colored specimen set than for the medium- or dark-colored sets, except for two sites that showed statistically similar results for medium-colored specimens but were significantly different from the dark-colored set. Among the different research sites, sites 2 and 5 registered significantly higher PT thresholds for the light specimens (1.5 and 1.6, respectively), and site number 1 had a significantly higher AT threshold relative to the other sites. The 50:50% perceptibility and acceptability thresholds were significantly different among light-, medium-, and dark-colored specimens for different research sites and observer groups. CLINICAL SIGNIFICANCE: The visual perception of color difference related to light-, medium-, and dark-colored specimens varied based on observer group and their geographic location. Therefore, a greater understanding of factors that affect visual thresholds, with the observers being "the most forgiving" for color differences among the light shades, will allow diverse clinicians to overcome some of the challenges of clinical color matching.

Exploring the CIEDE2000 thresholds for lightness, chroma, and hue differences in dentistry.

OBJECTIVE: To evaluate the perceptibility and acceptability CIEDE2000 (KL:KC:KH) thresholds for lightness, chroma and hue differences in dentistry. METHOD: A Python-based program was developed to conduct a psychophysical experiment based on visual assessments of computer-simulated images of human teeth. The experiment was performed on a calibrated display. A 40-observer panel: dentists and laypersons (male and female; n=10), evalu- ated three subsets of simulated human teeth: the lightness subset (%∆L00 ≥ 98 %), the chroma subset (%∆C00 ≥ 98 %) and the hue subset (%∆H00 ≥ 98 %), using ∆E00 ≥ 5 units. A Takagi-Sugeno-Kang Fuzzy Approximation model was used as fitting procedure, and 50:50 % lightness, chroma and hue CIEDE2000 (1:1:1) and CIEDE2000 (2:1:1) perceptibility (PT00) and accept- ability (AT00) thresholds were calculated. Data was statistically analyzed using t-test (p < 0.05). RESULTS: The 50:50 % PT00 for KL=1 were ∆L00=1.04, ∆C00=1.58 and ∆E00=1.01; and for KL=2 were ∆L00=0.51, ∆C00=1.58 and ∆E00=0.71. The 50:50 % AT00 for KL=1 were ∆L00=2.82, ∆C00=3.04 and ∆E00=2.66; and for KL=2 were ∆L00=1.40, ∆C00=3.04 and ∆E00=1.78. PT00 and AT00 ∆H00 may be considered no computable. A significant difference was found between CIEDE2000(1:1:1) and CIEDE2000(2:1:1), between lightness and chroma metrics, and between observer groups. No differences for lightness and chroma PT00 were found between male and female groups. CONCLUSIONS: It is important to use PT00 and AT00 for lightness, chroma and hue specific to evaluate perceptual sensitivity for color changes in the tooth color space. AT00 for lightness and chroma are influenced by the observer's experience and gender. Males and laypersons show more tolerance for changes in chroma (∆C00) and in lightness (∆L00). SIGNIFICANCE: Hue and chroma mismatch are more difficult to be accepted in dental color space.