Depletion Rate of Hydrogen Peroxide from Sodium Perborate Bleaching Agent

Internal bleaching of discolored teeth uses sodium perborate reacting with water to form the active agent, hydrogen peroxide (H₂O₂). Sodium perborate is replaced at varying time intervals depending on clinician preference and until esthetically acceptable results are achieved, but this is done without scientific basis. This study measured the depletion rate of hydrogen peroxide from sodium perborate as a bleaching agent.

Two sodium perborate bleaching products (Odontobleach [Australian Dental Manufacturing, Kenmore Hills, Queensland, Australia] and Endosure Perborate Micro [Dentalife, Ringwood, Victoria, Australia]) and distilled deionized water mixtures at ratios of 25 μg/mL, 50 μg/mL, and 100 μg/mL were placed into sealed microtubes and incubated at 37°C. H₂O₂ concentrations were measured at 23 time points over 4 weeks. Quantification of H₂O₂ concentrations was obtained using a ferrothiocyanate oxidation reduction reaction followed by spectrophotometry readings.

The H₂O₂ concentration rapidly peaked within 27 hours and reached a plateau by about 3 days (75 hours). Low levels of H₂O₂ were evident beyond 3 days and for at least 28 days. No significant differences were found between the 2 sodium perborate products. There was also no significant difference in the depletion rate between the different ratios.

Based on the chemistry of H₂O₂ depletion, the minimum replacement interval for the bleaching agent is 3 days. Frequent replacements of the perborate clinically may be unnecessary because of the continued presence of low H₂O₂ levels for at least 28 days. Although these data cannot be extrapolated to the clinical situation, they set a baseline for further studies to address the many clinical variables influencing internal bleaching.