Objective Image-Based Assessment of Tooth Translucency Changes Following Different Bleaching Protocols: A Retrospective Cohort Study

Background: Tooth bleaching is a conservative aesthetic treatment that may influence tooth translucency, an optical property relevant to biomimetic dentistry. The purpose of this study is to evaluate changes in tooth translucency after three bleaching protocols, while preliminarily testing an objective, image-based, and spatially resolved method. Materials and Methods: A retrospective analysis used data from a previously published randomised clinical trial comparing three bleaching systems: in-office 6% hydrogen peroxide paint-on varnish; at-home 6% hydrogen peroxide prefilled tray; and at-home 16% carbamide peroxide custom tray. Spectrophotometric images of maxillary central incisors and canines were retrieved at different stages, and their translucency maps were processed with ImageJ to quantify the percentage of translucent area, histogram-derived grey intensity and RGB-blue channel metrics. Statistical tests were performed appropriately (α = 0.05). Results: All bleaching protocols produced significant post-treatment increases in translucency-related parameters (p < 0.05), although the in-office protocol showed smaller changes than the at-home techniques (p < 0.05). At six months, the translucent area remained significantly higher in most conditions, whereas histogram-derived metrics showed no significant changes. Correlations between translucency-related parameters and colour/whiteness differences were mostly negligible to weak. Conclusions: The preliminary image-based assessment detected significant and technique-dependent changes in translucency-related parameters following bleaching, with a weak linear association between these changes and colour outcomes.