In situ evaluation of the bleaching efficacy of experimental hydrogen peroxide hydrogel with MnO-doped Biosilicate...

Hydrogen peroxide (HP) at 35% is effective for dental bleaching but may reduce enamel mineral content and induce structural changes. This study developed a bleaching-hydrogel containing 6%HP and manganese-oxide-doped Biosilicate (MnO_BioS), activated by violet LED, under in situ conditions. Pigmented enamel blocks were attached to palatal devices (n = 12) and kept intraorally for 15 days, being removed only for bleaching sessions. Experimental groups were as follows: 35%HP (positive control) and 6%HP gel containing BioS or MnO_BioS (0/10 wt%), with or without violet LED irradiation. Bleaching consisted of three 30-min sessions with 7-day intervals. Color change (ΔE₀₀), whiteness index (ΔWI_D), color coordinates (ΔL*, Δa*, Δb*), surface hardness recovery (%SHR), and enamel inorganic content (CO₃ ^2-/PO₄ ^3- ratio by Fourier-transform infrared) were evaluated at baseline (T₀) and after treatment (T₁), with scanning electron microscopy analysis at T₁. Data were analyzed using analysis of variance and Tukey's-test (α = 0.05). 6%HP_MnO_BioS_LED showed the highest bleaching effectiveness (ΔE₀₀ = 8.90 ± 1.18; ΔWI_D = 20.86 ± 3.26), surpassing 35%HP in ΔWI_D (15.53 ± 1.33) and showing comparable ΔE₀₀ (6.48 ± 1.81). MnO_BioS groups increased enamel CO₃ ^2-/PO₄ ^3- ratios after bleaching (0.475 ± 0.02; 0.466 ± 0.01) compared with baseline (0.431 ± 0.01; 0.429 ± 0.01; p < 0.05). Hardness recovery improved (%SHR = 4.14 ± 1.88; 5.45 ± 2.54), whereas it decreased in 35%HP (-1.32 ± 1.67) and 6%HP_LED (-2.60 ± 0.96). 6%HP hydrogel containing MnO_BioS activated by violet LED enhanced bleaching efficacy while preserving enamel mineral-related parameters.