Manganese oxide increases bleaching efficacy and reduces the cytotoxicity of a 10% hydrogen peroxide bleaching gel

OBJECTIVE

The study aims to assess the effects of a 10% H₂O₂ bleaching gel with different MnO₂ concentrations on the bleaching efficacy (BE), degradation kinetics (DK) of H₂O₂, and trans-amelodentinal cytotoxicity (TC).

MATERIALS AND METHODS

Standardized bovine enamel/dentin disks (n = 96) were placed in artificial pulp chambers, and the bleaching gels were applied for 45 min. Thus, the following groups were established: (G1) no treatment (negative control/NC); (G2) 35% H₂O₂ (positive control/PC); (G3) 10% H₂O₂; (G4) 10% H₂O₂ + 2 mg/mL MnO₂; (G5) 10% H₂O₂ + 6 mg/mL MnO₂; and (G6) 10% H₂O₂ + 10 mg/mL MnO₂. After analyzing bleaching efficacy (ΔE₀₀ and ΔWI), the degradation kinetics of H₂O₂ and trans-amelodentinal cytotoxicity were determined (n = 8, ANOVA/Tukey; p < 0.05).

RESULTS

G6 presented BE (ΔE₀₀ and ΔWI) statistically similar to G2, which represented conventional in-office bleaching (p = 0.6795; p > 0.9999). A significant reduction in the diffusion of H₂O₂ occurred in G3, G4, G5, and G6 compared to G2 (p < 0.0001). The highest DK of H₂O₂ occurred in G6 (p < 0.0001), which had the lowest TC in comparison with all other bleached groups (p ≤ 0.0186).

CONCLUSION

The addition of 10 mg/mL of MnO₂ in a 10% H₂O₂ bleaching gel potentiates the degradation of this reactive molecule, which increases the BE of the product and decreases TC.

CLINICAL SIGNIFICANCE

Replacing a 35% H₂O₂ gel commonly used for conventional in-office dental bleaching by a 10% H₂O₂ gel containing 10 mg/mL of MnO₂ reduces the cytotoxicity of this professional therapy, maintaining its excellent esthetic efficacy.

Increased whitening efficacy and reduced cytotoxicity are achieved by the chemical activation of a highly concentrated hydrogen peroxide bleaching gel

OBJECTIVE

This study was designed for the chemical activation of a 35% hydrogen peroxide (H2O2) bleaching gel to increase its whitening effectiveness and reduce its toxicity.

METHODOLOGY

First, the bleaching gel - associated or not with ferrous sulfate (FS), manganese chloride (MC), peroxidase (PR), or catalase (CT) - was applied (3x 15 min) to enamel/dentin discs adapted to artificial pulp chambers. Then, odontoblast-like MDPC-23 cells were exposed for 1 h to the extracts (culture medium + components released from the product), for the assessment of viability (MTT assay) and oxidative stress (H2DCFDA). Residual H2O2 and bleaching effectiveness (DE) were also evaluated. Data were analyzed with one-way ANOVA complemented with Tukey's test (n=8. p<0.05).

RESULTS

All chemically activated groups minimized MDPC-23 oxidative stress generation; however, significantly higher cell viability was detected for MC, PR, and CT than for plain 35% H2O2 gel. Nevertheless, FS, MC, PR, and CT reduced the amount of residual H2O2 and increased bleaching effectiveness.

CONCLUSION

Chemical activation of 35% H2O2 gel with MC, PR, and CT minimized residual H2O2 and pulp cell toxicity; but PR duplicated the whitening potential of the bleaching gel after a single 45-minute session.