Efficacy and effects on enamel of low and high-concentrated bleaching gels for at-home and in-office techniques

To evaluate the efficacy of low and high-concentrated bleaching gels in both at-home and in-office techniques and their effects on enamel properties.

Bovine enamel/dentin specimens were randomly allocated to five groups (n=12): deionized water (negative control - DW), 6% hydrogen peroxide (6HP), 40% hydrogen peroxide (40HP), 10% carbamide peroxide (10CP), and 45% carbamide peroxide (45CP). For 6HP and 40HP, the gel was applied 3x20 minutes in 1 day. For 10CP and 45CP, the bleaching gels were applied 1x/day for 8 hours and 1x/day for 30 minutes over 7 days, respectively. Before and after bleaching treatment, color (CIE L*a*b*), surface microhardness (SMH), roughness (Ra), and gloss (GU) were assessed. Alterations in color (ΔE₀₀ and ΔWID), SMH (%SMHalt), Ra (%Raalt) and GU (%GUalt) were calculated. Data were analyzed by one-way ANOVA and Tukey's test (α= 0.05).

Significant differences were found for color alteration (P< 0.05). The group 10CP showed the highest color difference. The groups 40HP, 10CP, and 45CP exhibited similar values of ΔWID. No alteration in enamel microhardness and roughness was found (P> 0.05). Although significant differences were found for %GUalt between the groups (P< 0.05), they were not different from the negative control. The 10% carbamide peroxide resulted in the highest color alteration, while all tested bleaching gels were effective in producing color change that exceeded the acceptability threshold without causing damage to the enamel surface.

All bleaching gels can be considered safe in the tested protocol, and the greatest color difference was promoted by 10% carbamide peroxide overnight.