In vivo degradation of bleaching gel used in whitening teeth

Background. The purpose of the study described here was to determine the in vivo degradation rate of 10 percent carbamide peroxide, or CP, gel in blea ching trays. The degradation rate indicates the remaining concentration of the active agent on the facial surfaces at various intervals. Methods. The researchers fabricated bleaching trays with 0.5-millimeter res ervoirs and loaded them with a 10 percent CP whitening gel. The tray was se ated in place in 15 patients for six different intervals that ranged from 1 5 seconds to 10 hours. When the tray was removed, three samples were collec ted from each patient: the gel remaining in the tray; the adherent gel scra ped from the teeth; and a "grab" sample from the reservoir of tooth no. 8. The researchers analyzed these samples for CP according to the method speci fied by the U.S. Pharmacopeial Convention. Results. The percentage of CP recovered decreased as the intervals increase d: 87 percent at 15 seconds, 10 percent at 10 hours. Log of tray, teeth and grab samples, respectively, at 15 seconds were 0.94, 0.98 and 0.96 and at 10 hours were -0.13, -0.38 and 0.11. The first-hour degradation rate for tr ay, teeth and grab samples, respectively, was 2.0 times, 3.6 times and one time the rate during the next nine hours. The within-subject repeatability of the samples was excellent. Conclusions. The degradation rate of CP during the bleaching process is bie xponential: In the tray and teeth samples, the degradation rate was acceler ated during the first hour. Further research is needed to determine the cau se of this acceleration. Clinical Implications. The active agent in CP bleaching gel is available in bleaching trays for more than 10 hours. After two hours, more than 50 perc ent of the active agent is available, and 10 percent is available after 10 hours.