RESUMEN
This study evaluated the effect on enamel demineralization of 10% hydrogen peroxide (H2 O2 ) gels containing different concentrations of sodium trimetaphosphate (TMP) and sodium fluoride (NaF) combined with the daily use of fluoridated or placebo dentifrice. Bovine enamel blocks were selected by surface hardness (n = 72) and randomly assigned to one of the following experimental treatments: 10% H2 O2 ; 10% H2 O2 + 3% TMP + 0.1% NaF; and 10% H2 O2 + 0.3% TMP + 0.05% NaF, each with or without fluoridated dentifrice. H2 O2 -based gels were applied for 30 min d-1 followed by treatment with dentifrice (1 min). Enamels blocks were stored in artificial saliva at 37°C between sessions during the 14 days of experiment. Percentage of surface hardness loss (%SH) was calculated, and the blocks were cut into halves to analyze cross-sectional hardness (ΔKHN). Polarized light microscopy images were obtained of the longitudinal sections of the samples. Enamel treated with fluoridated dentifrice presented lower hardness loss than those treated with placebo dentifrice (%SH and ΔKHN). Use of TMP- and NaF-based gels, regardless of concentration, led to the lowest %SH values. Specimens treated with 10% H2 O2 gel had the highest %SH and ΔKHN values. Gels with 10% H2 O2 + 3% TMP + 0.1% NaF showed the lowest ΔKHN values. Microscopy images clearly showed that the addition of TMP and NaF to the H2 O2 -based gels was effective in reducing the loss of hardness, and the fluoridated dentifrice helped minimize it in all treatments.