OBJECTIVE: This in vitro study evaluated hydrogen peroxide (HP) penetration into the pulp chamber, bleaching efficacy, and surface enamel morphology of human teeth subjected to enamel microabrasion (MA) combined with in-office bleaching (IOB), with or without the application of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) remineralizing agent. METHODS: Forty sound premolars were randomly divided into four groups: no treatment (NT), IOB only (IOB), MA followed by IOB (MA+IOB), and MA followed by CPP-ACP and then IOB (MA+CPP-ACP+IOB). HP concentration in the pulp chamber was measured using UV-Vis spectrophotometry, while bleaching efficacy was assessed with a digital spectrophotometer. Surface morphology was analyzed using scanning electron microscopy (SEM), and data were statistically analyzed. RESULTS: The NT group exhibited lower HP penetration compared to experimental groups, while MA+IOB showed higher HP levels than IOB and MA+CPP-ACP+IOB. All experimental groups demonstrated significant color changes, except NT. The MA+IOB group displayed more grooves on enamel surfaces than the MA+CPP-ACP+IOB group, which had remineralizing agent deposits. CONCLUSION: Combining MA and IOB increases HP penetration into the pulp chamber, but using CPP-ACP after MA can mitigate this effect without compromising bleaching efficacy. CLINICAL SIGNIFICANCE: Employing a CPP-ACP remineralizing agent post-microabrasion can help reduce HP levels in the pulp chamber while maintaining effective whitening.