Color Change and Cytotoxic Effects of a Bleaching Gel With 22% Carbamide Peroxide Catalyzed by Manganese Oxide

Objectives: To evaluate the color change and trans-amelodentinal cytotoxicity of a 22% carbamide peroxide (CP) bleaching gel containing different concentration of manganese oxide (MnO₂).

Material and methods: Enamel/dentin discs adapted to artificial pulp chambers were distributed according to treatments: CN-No treatment; CP22%-22%CP; CP22 + 2MnO₂-22%CP + 2 mg/mLMnO₂; CP22% + 6MnO₂-22%CP + 6 mg/mLMnO₂; CP22% + 10MnO₂-22%CP + 10 mg/mLMnO₂ applied for 2 h for 15 days. Color change-CC (ΔE₀₀ and ΔWI_D) (n = 8) was determined at 5, 10, and 15-day periods (ANOVA/Sidak). Trans-amelodentinal cytotoxicity (TC) was assessed after applying the extracts to cultured MDPC-23 cells, which were analyzed concerning their viability (Vi) (n = 8) and oxidative stress (OxS) (n = 8). The amount of hydroxyl radical (OH^•) (n = 4) generated by H₂O₂ degradation (ANOVA/Sidak), and trans-amelodentinal diffusion of H₂O₂ (n = 8) (ANOVA/Tukey) were also evaluated.

Results: CP22 + 10MnO₂ presented higher CC than CP22 for both evaluated equations in all analysis periods (p ≤ 0.04). Among bleached groups, CP22 + 10MnO₂ presented the highest OH^• generation (p ≤ 0.02) and the lowest trans-amelodentinal diffusion of H₂O₂ (p ≤ 0.0004). Therefore, MDPC-23 cells in CP22 + 10MnO₂ exhibited the lowest OxS (p < 0.0001) and consequently the highest Vi (p ≤ 0.0146).

Conclusion: Besides increasing the bleaching efficacy, the strategy of adding 10 mg/mL of MnO₂ to a 22%CP bleaching gel also reduces significantly the trans-amelodentinal diffusion of H₂O₂, diminishing the cytotoxicity caused by at-home bleaching therapy.

Clinical significance: The addition of MnO₂ to a 22% carbamide peroxide bleaching gel improves the color change and reduces the cytotoxicity effects of the product, making at-home bleaching faster and biologically safer.