Efficacy of 35% hydrogen peroxide on human enamel: in vitro evaluation in different tooth areas.

This study aimed to assess the efficacy of a 35% hydrogen peroxide--based gel without activation in vitro on three areas of the tooth surface. Vestibular faces of human premolar teeth were darkened, followed by two whitenings at 7-day intervals. The efficacy of whitening was determined in the cervical third, medium third and incisal third of the tooth surface with an Easyshade-Vita spectrophotometer based on the CIELab system. The L, a, b parameters were determined for each third by the identification of high luminosity and hues tending to green and yellow; pigmentation luminosity was then reduced, and the parameters a and b became reddish and yellowish, respectively. Seven days after the first whitening, there were significant improvements in L and a values. Seven days after the second whitening, the three parameters returned to values close to the initial values; the b parameter was most strongly correlated with whitening efficacy. DE values revealed a visually perceptible difference. There was a satisfactory removal of pigmentation after both whitenings, while the lack of uniformity among the tooth-surface thirds after the first session justified the performance of two whitening procedures. With regard to each third, DE indicated a visibly perceptible difference, although L, a and b values showed no statistically significant differences.