Measurement Aperture Size Dependent Spectroradiometric Color of Composite-Resins

Objectives: Spectroradiometry was developed to overcome the edge-loss problems of spectrophotometric color of translucent objects; however, the spectroradiometric color of an object might be influenced by the measurement protocols. Our objective was to determine the influence of measurement aperture size on the color coordinates (CIE L*, a* and b*) and translucency of composite resins. Methods: Two brands of composite resins (A1, A2, A3, and A3.5 shades; a total of 8 shades) were investigated. Specimen (12 mm in diameter and 1 mm in thickness) color was measured by a spectroradiometer (PR 680; Photo Research, Chatsworth, CA, USA) over black and white backgrounds with different measurement aperture sizes (1.32, 2.63, and 5.25 mm) achieved by changing the viewing angle of the spectroradiometer. Translucency parameter (TP) was calculated as the color difference between specimens over the black and white backgrounds. The influence of measurement aperture size and the brand and shade of composite resins on the color parameters (CIE L*, a*, b* and TP) was analysis by three-way analysis of variance. Correlations among the color parameters measured with different aperture sizes were analyzed by regression analysis. Results: The color parameters were influenced by the measurement aperture size and the brand and shade of composite resins (p < 0.05). There were significant correlations between the color parameters measured with different aperture sizes (r = 0.953-0.999, p < 0.01). The CIE L*, a*, b* and TP values increased as the measurement aperture size increased. Conclusion: The measurement aperture size of a spectroradiometer influences the measured color of composite resins; higher values were obtained when a larger aperture size was used. Measurement aperture size should be considered when comparing the optical properties measured with a spectroradiometer. Furthermore, standardized measurement protocols should be developed for spectroradiometric color.