Reactivation capacity of TiO2 nanoparticles for dental bleaching: an in vitro study

This study evaluated the bleaching efficacy, pH behavior, and reuse potential of a titanium dioxide nanoparticle (TiO₂) suspension as a photocatalytic, peroxide-free alternative to carbamide peroxide (CP) for at-home bleaching. Forty bovine incisors were subjected to a 21-day at-home bleaching regimen (2 h/day) using fresh or reused agents (n = 10): fresh CP (16% CP), reapplied CP (16% CP collected and reused), fresh TiO₂ (10 wt% TiO₂ suspension), and reapplied TiO₂ (reactivated 10 wt% TiO₂ suspension). TiO₂ suspensions were UV-activated daily (385 nm, 50 min), and the reused TiO₂ was reactivated prior to each application. The pH of the bleaching agents was assessed before gel application and after completion of the at-home protocol; all experimental groups showed a similar pH trend, with values increasing from 6.0 to 7.0 throughout the procedure. Bleaching efficacy was evaluated using CIEDE2000 (ΔE₀₀) and whiteness index (ΔWID) values obtained with a digital spectrophotometer (VITA Easyshade V). Data were analyzed with one-way ANOVA and Tukey's test (α = 0.05). ΔE₀₀ analysis showed that fresh TiO₂ produced the lowest color change, with values closest to the perceptibility and acceptability thresholds, differing significantly from reapplied TiO₂, fresh CP, and reapplied CP (p < 0.05). No significant differences were observed among the remaining groups, and all other conditions exhibited ΔE₀₀ values above the acceptability threshold. ΔWID values did not differ significantly among groups (p = 0.475). The UV-activated TiO₂ suspension (100 min total exposure) was able to bleach teeth without peroxide.