To evaluate the penetration of hydrogen peroxide into the pulp chamber, color change, and enamel morphology of human teeth with different substrates (sound and white spot), subjected to the application of a resin infiltration (RI) and in-office bleaching at different time intervals (immediately and 7 days after RI application).

Fifty-four sound human premolars were randomly distributed into six groups (n = 9), all subdivided according to substrate (sound and white spot): bleaching with 35% hydrogen peroxide only (HP); RI followed by immediate bleaching (RI/HPi); and RI followed by bleaching after 7 days (RI/HP7d). The concentration of hydrogen peroxide (µg/mL) was measured by UV-Vis spectrophotometry, color change was evaluated using a digital spectrophotometer (ΔE₀₀ and WI_D), and enamel surface morphology was analyzed by scanning electron microscopy (SEM) (α = 0.05).

In the groups without RI (HP), teeth with white spot lesions showed approximately 40% greater hydrogen peroxide penetration than sound teeth (p = 0.15). RI significantly reduced this penetration, regardless of the substrate or bleaching time (p > 0.02). According to WI_D values, the groups treated with RI (RI/HPi and RI/HP7d) achieved a final color similar to that of sound enamel treated with 35% HP. Enamel morphology was more homogeneous in the groups that received resin infiltration.

The application of RI prior to in-office bleaching significantly reduced hydrogen peroxide penetration into the pulp chamber without compromising bleaching efficacy. In teeth with white spot lesions, it led to a final shade comparable to that of sound teeth and resulted in a more uniform enamel morphology.

Resin infiltration is an effective, minimally invasive approach for treating white spot lesions, improving bleaching outcomes and limiting hydrogen peroxide penetration.