Lightness, chroma and hue differences on visual shade matching

Objectives: To analyze the influence of lightness, chroma and hue differences on visual shade matching performed by dental students.

Methods: 100 dental students (DS) volunteers with normal vision participated in the study. A spectroradiometer (SP) was used to measure the spectral reflectance of 4 extracted human upper central incisors (UCI 1-4) and shade tabs from Vita Classical (VC) and Vita Toothguide 3D-Master (3D) shade guides. Measurements were performed over a gray background, inside a viewing booth and under D65 illuminant (diffuse/0° geometry). Color parameters (L*, a*, b*, C* and h°) were calculated. DS used VC and 3D to visually select the best shade match for each UCI. CIE metric differences (Δa^*,Δb^*,ΔL^', ΔC^' and ΔH^') and CIEDE2000(2:1:1) lightness (ΔE_L), chroma (ΔE_C) and hue (ΔE_H) differences were obtained from each UCI and the first three shades selected by DS and the first option using CIELAB, CIEDE2000(1:1:1) and CIEDE2000(2:1:1) color difference metrics. The closest CIELAB color-discrimination ellipsoid (from RIT-DuPont visual color-difference data) to each UCI was selected for the analysis of visual shade matching.

Results: DS showed a preference for shades with lower chroma (ΔC^' and ΔE_C) and/or hue (ΔH^' and ΔE_H) values instead of shades with lower lightness values (ΔL^' and ΔE_L). Most best visual matches were near the tolerance ellipsoid centered on tooth shade.

Significance: This study is an attempt to partially explain the inconsistencies between visual and instrumental shade matching and the limitations of shade guides. Visual shade matching was driven by color differences with lower chroma and hue values.