AbstractAimThis study evaluated the efficacy and cytotoxicity of 35% hydrogen peroxide (HP) gel incorporated with 10% (w/w) biosilicate (BioS) on sound enamel and early‐stage enamel erosion lesions.MethodsDiscs of enamel/dentin were selected, subjected to erosive cycles (0.3% citric acid, pH 2.6), and treated with (n = 8): HP (35% HP, positive control); HP_BioS [carboxymethyl cellulose (CMC) + HP + BioS]; BioS (CMC + BioS); CMC (negative control). The discs were adapted to artificial pulp chambers with the enamel exposed for bleaching, and the dentin facing toward the culture medium (Dulbecco's modified Eagle's medium [DMEM]). Bleaching was performed in three 30‐min sessions at 7‐day intervals. After bleaching, the diffusion product (DMEM extract + diffused HP) was pipetted onto MDPC‐23 odontoblastic cell line and inoculated. Color parameters (ΔL, Δa, Δb), color change (ΔE₀₀), and changes in whiteness index (ΔWI_D) were determined before (T₀) and after the last bleaching session (T₃). Cell viability (MTT, %), H₂O₂ diffusion (μg/mL), oxidative cell stress (OxS), and cell fluorescence (live/dead assay, in confocal microscopy) were assessed (ANOVA/Tukey; α = 0.05).ResultsNo difference in ΔL, Δa, Δb, ΔE₀₀, and ΔWI_D were found between HP and HP_BioS (p > 0.05). The incorporation of BioS decreased the HP diffusion into the substrates and mitigated oxidative stress in early‐stage eroded enamel (p < 0.05). HP_BioS presented significantly higher cell viability compared with HP under erosion conditions. Live/dead assay indicated that BioS_HP maintained viability with larger clusters of viable cells.ConclusionIncorporating BioS into HP maintained bleaching effectiveness, favored cell viability, reduced the oxidative stress, and the cytotoxicity in teeth with early‐stage erosion.Clinical SignificanceBioS formulation showed promising results for reducing cytotoxicity in patients seeking tooth bleaching and presenting undetectable early‐stage erosion.