Evaluating visual thresholds and color metrics in dental research: An exploratory study

This study aimed to evaluate perceptibility (PT) and acceptability thresholds (AT) for multiple color measurement devices and assess the performance of three color difference equations (∆E*_ab, ∆E₀₀, and ∆E₉₄) using a visual dataset from expert observers.

A visual dataset previously published was extended by adding the x-rite MetaVue spectrophotometer and ∆E₉₄ to the analysis. Visual scaling was performed on 26 sample pairs of teeth using magnitude estimation. Observers answered PT and AT questions to determine thresholds. Threshold estimation was conducted using a model-free method, and device performance was analyzed using the standardized residual sum of squares (STRESS) index and visual instrument agreement scale (VIAS).

The PT and AT thresholds varied across devices and color difference equations. For ∆E₀₀, STRESS values ranged from 23 to 32 (mean 29, sd 2.9), with VIAS scores between 68 % and 77 % (mean 71 %, sd 2.9). ∆E₉₄ showed higher STRESS values (24-42, mean 34, sd 5.5) and lower VIAS scores (58-76 %, mean 66 %, sd 5.5). ∆E*_ab demonstrated excellent visual-instrumental agreement with STRESS values from 18 to 36 (mean 24, sd 5.9) and lower VIAS scores (82-64 %, mean 76 %, sd 5.9) outperforming ∆E₉₄ and ∆E₀₀. The x-rite MetaVue achieved excellent results under controlled conditions but it is unsuitable for clinical research due to its design.

This study highlights the variability in PT and AT across devices, suggesting the need for device-specific thresholds. It also demonstrates the effectiveness of ∆E*_ab in dental colorimetry compared to more complex color difference metrics.