RESUMO
BACKGROUND: The authors conducted a study to quantify the amount of hydrogen peroxide remaining after in-office bleaching and to investigate the effectiveness of 35 percent sodium ascorbate (SA) on removal of the bleaching agent from dentin. METHODS: The authors sectioned 70 extracted human third molars to form 4×4×2-millimeter blocks of dentin and then categorized them into eight groups as follows: group 1, no bleaching; group 2, bleaching (35 percent hydrogen peroxide) and daily measurement; group 3, bleaching plus one application of 35 percent SA for 60 minutes; group 4, bleaching plus one application of SA for 10 minutes; group 5, bleaching plus two applications of SA for 10 minutes each; group 6, bleaching plus two applications of SA for five minutes each; group 7, bleaching plus three applications of SA for one minute each; and group 8, bleaching plus two applications of SA for one minute each. They quantified the amount of residual hydrogen peroxide by using a colorimetric assay with horseradish peroxidase and o-phenylenediamine dihydrochloride as the enzyme and substrate, respectively. RESULTS: The authors analyzed the data by using the Kruskal-Wallis test (α = .05). The results showed that no hydrogen peroxide remained after 120 hours in group 2 and at their respective measurement points in groups 5, 6, 7 and 8, whereas hydrogen peroxide had been removed only partially in groups 3 and 4. CONCLUSION: Two applications of 35 percent SA for one minute each produced the same result--complete removal of the bleaching agent--as that observed five days after tooth bleaching with 35 percent hydrogen peroxide without any application of SA. CLINICAL IMPLICATIONS: In an appropriate concentration, SA facilitates rapid elimination of residual peroxide up to two minutes after bleaching with 35 percent hydrogen peroxide. This finding suggests that clinicians can perform bonding procedures shortly after the bleaching procedure.