The influence of two home-applied bleaching agents on enamel microhardness: an in situ study

OBJECTIVE: This in situ study evaluated the influence of two home-applied bleaching agents (10% carbamide peroxide and 7.5% hydrogen peroxide) on enamel microhardness. METHODS: Ninety enamel slabs were obtained from human third molars and baseline Knoop hardness measurements were recorded under a 50 g load for 5s. The specimens were attached to intra-oral devices delivered to 10 volunteers (donor of the teeth) who used the devices 24h/day throughout the experiment. The specimens were divided in three groups, two experimental and one control; in the last group, enamel slabs were not submitted to bleaching agents, but exposed only to the action of saliva. Two custom-made trays were made for each volunteer to recover the teeth and the appliances containing the enamel slabs. The bleaching regimen was 1h/day for 21 consecutive days. Subsequently, additional hardness measurements were recorded. RESULTS: The mean values of the baseline and final microhardness were: 348 and 352.2; 346.6 and 354.5; 342 and 340.8, for control, 10% carbamide peroxide and 7.5% hydrogen peroxide groups, respectively. One-way ANOVA of the microhardness mean values revealed no statistically significant differences among groups, the specimens treated with 7.5% hydrogen peroxide has shown a tendency (p=0.056) to microhardness decrease. CONCLUSIONS: Data suggested that the tested home bleaching agents did not change the superficial enamel microhardness.