VANCOUVER, British Columbia -- Scientists in the University at Buffalo School of Dental Medicine have preliminary evidence, based on research in an animal model, that hydrogen peroxide, a major ingredient in dental bleaches and in some whitening toothpastes, may be a cancer promoter.
"Our research appears to show that the use of hydrogen peroxide in certain strengths can promote lesions that have already begun to develop in the oral cavity," said Barry C. Boyd, D.M.D., lead researcher on the study. "The recent increase in oral use of hydrogen peroxide, especially with the advent of cosmetic dentistry, has brought this issue to the fore."
Results of the study were presented here today (March 12, 1999) at the combined meeting of the American Association for Dental Research and the International Association for Dental Research.
Earlier studies, including some done at UB, have shown mixed results on hydrogen peroxide's role as a possible cancer initiator and promoter, defined as an agent that can cause cancer only after cells already have begun to behave abnormally. The goal of the current study was to determine the rate of cancer progression, if any, when pre-cancerous cells were in frequent contact with hydrogen peroxide.
The researchers used photofluorescence as a measure of cancerous progression. Photofluorescence is based on the propensity of Photofrin, a light-sensitive drug, to accumulate in cancer cells. When exposed to light, cells that are changing or are already cancerous will stand out from normal cells due to the accumulation of the light-sensitive drug.
"There is a high correlation between increased fluorescence and neoplastic changes (abnormal cell growth)," Boyd said. To examine hydrogen peroxide's cancer-promoting activity, researchers applied a 3-percent hydrogen-peroxide solution to premalignant lesions in the right cheek pouches of hamsters. Hydrogen peroxide was applied three times a week for 12 weeks.
Boyd said many dental practitioners use 3-percent hydrogen peroxide as a rinse or to debride oral wounds.
Lesions in the hamsters' left cheek pouches, not subject to hydrogen peroxide, served as controls.
Photodetection showed significantly more fluorescence in the cheek-pouch lesions exposed to hydrogen peroxide than in lesions not exposed. These findings suggest that this common bleaching agent may be a cancer promoter, Boyd said. He noted that a definitive answer is expected with the next phase of the research, which will be examination of tissue samples.
Additional researchers involved in the study were Thuan C. Loi, a dental student; Thomas S. Mang, Ph.D., clinical associate professor, and Charles Liebow, professor, all from the UB Department of Oral and Maxillofacial Surgery.