Objectives:
To assess the penetration of hydrogen peroxide (HP) into the pulp chamber and the bleaching efficacy on teeth with white spot lesions (WSLs) compared to sound teeth, when subjected to both in-office and at-home bleaching treatments.

Materials and methods:
Forty premolars were allocated into four groups (n = 10 each): sound teeth and teeth with artificially induced WSLs, both subjected to at-home bleaching (16% carbamide peroxide) and in-office bleaching (35% hydrogen peroxide). WSLs were induced in half of the specimens using a 14-day pH-cycling protocol alternating between demineralizing and remineralizing solutions. HP permeability (µg/mL) and color parameters (L*, a*, b*, and WID) were quantitatively assessed using a Cary UV-Vis 100 spectrophotometer and a VITA Easyshade Advance 4.0 digital spectrophotometer, respectively. Statistical analyses were performed using two-way and three-way ANOVA, with post hoc comparisons by Tukey’s, at a significance level of α = 0.05.

Results:
WSLs subjected to in-office bleaching exhibited higher HP penetration compared to the other groups (p < 0.05). After bleaching, WSLs showed significantly lower L* and WID values than sound teeth, regardless of the bleaching protocol or time point (p < 0.05). For a*, higher values were observed in WSLs after at-home bleaching, while for b* values no significant differences were found (p > 0.05). No significant difference in WID was observed between bleaching methods for WSLs teeth (p > 0.05).

Conclusions:
White spot lesions exhibited greater HP permeability and less favorable optical outcomes compared to sound teeth, particularly after in-office bleaching.

Clinical relevance:
Teeth with white spot lesions are more susceptible to HP diffusion and present less favorable whitening results. At-home bleaching may be a safer and more esthetically favorable conservative treatment option for managing white spot lesions.