Impact of remineralizing agents on enamel microhardness recovery after in-office tooth bleaching therapies

Objective. It has been shown that bleaching with 35/38% hydrogen peroxides may alter both enamel morphology and mineral content. This study aimed to analyze the morphology and microhardness of enamel bleached with in-office hydrogen peroxides and exposed toremineralizing agents. Materials and methods. After recording initial enamel morphology and microhardness, 60 bovine incisors were bleached using either a calcium-containing 35% hydrogen peroxide (Whiteness HP Blue) or a calcium-free 35% hydrogen peroxide (Whitegold Office) (n = 30). Then, the teeth were subjected to one of three post-bleaching remineralizing treatments (n = 10): storage in artificial saliva only, application of a sodium fluoride gel or application of a nanohydroxyapatite-based agent (Nano-P). After 24 h and 14 days of post-bleaching treatments, the enamel morphology and microhardness were re-evaluated. The microhardness data were analyzed by means of two-way ANOVA with repeated measurements and Tukey tests (p < 0.05), while the enamel morphology was analyzed descriptively. Results. Samples exposed to Nano-P presented statistically the highest microhardness 24 h after its application in comparison with other remineralizing agents. The microhardness recovery did not occur in any of the groups 14 days after treatment. The morphology of all samples 14 days after the application of all remineralizing agents presented a higher number of irregularities. Conclusion. Although some remineralizing products provided microhardness recovery and a positive effect on enamel morphology at 24 h post-bleaching, none of them were able to maintain microhardness and enamel morphology at 14 days post-bleaching.