Objective: DE* is commonly used in clinical research to assess overall color change. Because this parameter only reports non-directional, overall color change, mean DE* is less sensitive with respect to detecting between-treatment, 3-dimensional (DL*, Da*, Db*) color differences. This research reports an alternative statistical methodology used to simultaneously investigate 3-dimensional color differences between treatments for clinical trials applications. Methods: Data from a randomized, comparative clinical trial involving two bleaching systems (6.0% hydrogen peroxide whitening strips or 10% carbamide peroxide gel/dentifrice/rinse combination system) were analyzed using a repeated measures model. Outcomes were assessed separately at each visit to investigate location differences between the treatments in the 3-dimensional color space (DL*, Da*, Db*). Results: For yellow (Db*), the strip group experienced 0.59, 0.72 and 1.26 unit mean improvements over the combination group, with these treatments differing significantly (p < 0.05) at Days 3, 8 and 15 respectively. At Day 15, groups were highly significantly (p=0.0004) different with respect to DE*, favoring the 6.0% whitening strip. However, groups did not differ significantly in overall mean color at the intermediary time points Day 8 (p=0.10) or Day 3 (p=0.70) using the conventional DE* approach. In contrast, the 3-dimensional (DL*, Da*, Db*) analysis showed highly significant differences between treatments at Day 15 (p=0.004) and at the intermediary time point Day 8 (p=0.007), with directional evidence at Day 3 (p=0.18). Conclusion: Repeated measures modeling of 3-dimensional color differences may provide additional sensitivity to detect overall color differences compared to a two-sample t-test of DE*.

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