Effect of Non-Perpendicular Measurement Orientation on Easyshade Color Measurement

Small color measuring devices, like Easyshade digital spectrophotometer (Vita/Vident), are used in clinical and research applications, but potential measurement error has not been extensively reported. Objectives: This investigation examined effects of Easyshade measuring probe orientation on Vita shade selection and CIELAB color coordinates. Methods: Vita A1, A4, B2, B3, and C2 shade guide tabs were mounted on white backgrounds. Easyshade measurements were made in the middle third of each tab with the measuring probe oriented perpendicular to the surface, and also angled incisally and cervically 2.5°, 5°, 7.5°, 10°, 12.5°, and 15°. For each tab, the probe was initially oriented perpendicular and then maintained in that position by securing it to the vertical rod of a dental surveyor using a universal joint. Tab/background specimens were held on the survey table and rotated to each measurement angle. Angulation was confirmed visually using a protractor-type device. Shade designations and CIE color coordinates were recorded at each orientation. Color differences, ΔL, Δa, Δb, and ΔEab, were calculated between each angulation and the perpendicular position (control) for each tab. Results: Vita shade selection remained unchanged for all tabs at measurement angles ≤5°, but changed to adjacent shade designations at angles ≥7.5° (Classical=1tab, 3D=4tabs). ANOVA revealed statistical differences (p<0.01) in color difference for measurement direction (ΔEab±SD cervical=1.06±0.70, incisal=0.83±0.51, n=30ea) and angulation. For cervical/incisal directions combined, mean ΔEab±SD(Duncan's subsets) were: 2.5°=0.36±0.26(A), 5°=0.32±0.23(A), 7.5°=0.81±0.25(B), 10°=1.00±0.34(B), 12.5°=1.34±0.31(C), 15°=1.84±0.44(D) (n=10ea). Conclusion: Under the conditions of this study, shade selection by Easyshade is consistent at probe orientations within 5° of perpendicular to the measured surface. Results of Seghi et al (1989) suggest that color differences at angulations ≤10° would be visually insignificant for most observers, even in discriminating shade-matching environments. Results of Johnston and Kao (1989) suggest that differences for all angulations would be clinically insignificant for many observers.