Effect of Bleaching on Enamel with Early Artificial Carious Lesions

Some studies have shown alterations of the histological aspects and composition of sound dental enamel after carbamide peroxide (CP) gel application. However, it is not known the effect of CP gels on early caries lesions. Objectives: To evaluate the effect of CP on artificial caries lesions during pH-cycling model. Methods: Human dental enamel blocks were randomly divided into three treatments (n=10): (AS) artificial saliva, pH 7.0; (PG) placebo gel (without CP), pH 7.0 and (CP) 10% CP gel, pH 6.8 (Rembrandt/Den-Mat). Polished enamel blocks with known surface microhardness were demineralized in 50 mM acetate buffer; 1.23 mM Ca; 0.73 mM PO₄, pH 5.0 for 32 h at 37^oC. The blocks were submitted to a 12-day pH-cycling consisted of five phases: (1) fluoridated dentifrice (1100 ppm F as NaF)/water slurries three times a day to simulate daily toothbrushing; (2) between the treatments with dentifrice, enamel blocks were individually immersed in artificial saliva at 37^oC; (3) to simulate the daily acid challenge, enamel blocks were individually immersed in demineralized solution for 2 h at 37^oC; (4) the blocks were immersed in human saliva during 2 h to promote acquire pellicle formation before bleaching treatment; (5) to simulate daily whitening treatment, the blocks were submitted to CP, PG or AS overnight for 8 h at 37^oC. Surface microhardness was determined in the enamel blocks before, after demineralization and after pH-cycling. The percentage of surface microhardness recovery (%SMHR) was calculated. Results: The results (mean±SD) of the %SMHR according to the treatments AS, PG and CP were respectively: 3.3±3.5a, 1.4±1.5ab and 0.1±1.8b (p<0.05, Newman-Keuls test). Conclusion: These data demonstrated that enamel blocks treated with 10% CP gel showed lower surface microhardness recovery than unbleached group (AS), suggesting that bleaching procedures on early caries lesion should be indicated with caution (FAPESP # 02/04135-3).