Abrasion in human teeth brushed with toothbrush and dentifrice was evaluated quantitatively by SEM. Specimens which included surface enamel and cementum were cut from unerupted wisdom teeth. Controlled brushing was carried out by a brushing machine, with dentifrice or saline, for periods of five and ten minutes. Scratches were counted using SE micrographs. No scratches were observed on the enamel surfaces, due probably to its hardness. The cementum surfaces revealed scratches, the number increasing with the duration of burshing. Brushing with saline was much less abrasive than with dentifrice. It was concluded that damage to the cementum is caused primarily by the dentifrice, brushing per se being a minor factor.