Reliability of Three Image-Based Instrumental Color-Measurement Methods

To compare the precision of three clinically applicable, image-based color assessment methods-smartphone imaging, a clinical colorimeter (Optishade), and a digital scanning device (Borea Cobra)-against a benchtop spectrophotometer for measuring CIELAB coordinates and CIEDE2000 (ΔE₀₀) color differences of composite resin shades.

Three specimens from eight composite shades were measured using a benchtop spectrophotometer (reference) and the three test devices. Agreement for L*, a*, and b* was evaluated using linear regression and Bland-Altman analyses. ΔE₀₀ values relative to the reference and intershade ΔE₀₀ across shade pairs were analyzed using two-way ANOVA and regression.

Optishade showed the closest agreement with the reference-with slopes near unity, high R² values-and the smallest biases and limits of agreement. Borea Cobra demonstrated good overall performance and strong agreement for a* and b*, though with greater data dispersion and device-specific distortions in intershade differences. Smartphone measurements displayed systematic positive bias, lower slopes for chromatic axes, and wider limits of agreement, indicating reduced precision and compression of color differences.

Optishade provided the most reliable quantitative measurements; Borea Cobra offered acceptable performance with specific limitations. Smartphone-based imaging preserved shade ordering but was unsuitable for precise color quantification.