Harmonization of Color Measurements for Instruments Using d/8°Geometry: Pilot Study

Objectives: To create a standardized protocol for harmonization of color measurements of translucent dental materials for instruments using d/8° optical geometry.
Methods: A variety of dental materials were used to create square-shaped (10×10mm, 1.0mm thick) specimen sets A-P, 1-10 and I-X (16, 10 and 10 specimens per group, respectively), with variability of shades (light, medium, dark) and translucencies (medium, high). Contact-type measurements were performed at the middle portion of specimens using two spectrophotometers with d/8° optical geometry: reference measurements (RM) – at coordinating center, and site measurement (SM). Upon comparison of RM and SM reflection data, CF was calculated for SM and reflection data were adjusted accordingly. Color differences were calculated using CIELAB formula. Means and standard deviations were calculated. ANOVA and Fisher’s PLSD test was used to compare color differences (ΔE*) at a = 0.05.
Results: Means (standard deviations) of color differences (ΔE*) between RM and non-corrected SM for the same set (SM_NC), and between RM for each set and SM corrected with CFs for each set (SM_{CF (A-P)}, SM_{CF (1-10)}, and SM_{CF (I-X)}), are presented in the table.

RM-SM_NC vs. RM-SM_CF exhibited significant decrease of color differences for all three sets of specimens (p<0.0001). Fisher’s PLSD intervals for comparison among RM, SM_NC and RM-SM_CF for A-P, 1-10 and I-X sets were 1.7, 1.9 and 1.3, respectively.
Conclusions: Within the limitation of this pilot study, correction of site measurements with Correction Factor significantly increased agreement between different instruments with d/8° optical geometry when measuring translucent dental materials.