Visual and instrumental shade matching using CIELAB and CIEDE2000 color difference formulas

Abstract

Objectives: To compare visual and instrumental shade matching performances using two shade guides and three color difference formulas.

Methods: One hundred dental students (DS) volunteers (35 males and 65 females) with normal color vision participated in the study. The spectral reflectance of 4 extracted human upper central incisors (UCI) and shade tabs from Vita Classical (VC) and Vita Toothguide 3D-Master (3D) shade guides were measured using a spectroradiometer (SP) under D65 illuminant (diffuse/0° geometry) inside a viewing booth with a gray background. Color coordinates (CIE L*, a*, b*, C* and h°) were calculated according to CIE D65 illuminant and CIE 2° Standard Observer. Color coordinates of UCI were also evaluated using a dental spectrophotometer (EA - Easyshade Advance). DS used VC and 3D to visually select the best shade match for each UCI, under same experimental conditions used for the SP evaluation. Three color difference metrics (CIELAB, CIEDE2000(1:1:1) and CIEDE2000(2:1:1)) were used to calculate the best instrumental shade matching based on minimum color difference.

Results: The agreement between visual and instrumental shade matching was greater using SP (25-75%) than EA (0-25%). The percentage of best match for the visual assessment was more consistent using VC (23-55%) than 3D (19-34%). Considering the best performance (using SP and VC), the CIEDE2000(2:1:1) color difference formula showed the best estimate to the visual perception from DS.

Significance: Within the limitations of this study, combining the use of SP, CIEDE2000(2:1:1) and Vita Classical shade guide most closely represented the visual perception of DS. Instrumental shade determination should be accompanied by experienced human visual assessment.

Keywords: Color measurement; Dentistry; Shade matching; Spectroradiometer; Visual shade match.