The ability of two different toothbrush bristle ends to produce traumatic gingival abrasion was assessed in a double blind study of 15 male and 15 female young adults. Brushing was performed in a circular fashion using a modified Bass Technique. An apparatus allowing continuous visual feedback of the average brushing force permitted a degree of standardization of the system. The upper left canine and bicuspid area had to be brushed for 30 seconds with cut toothbrush bristles (CP) and with round ended toothbrush bristles (RP) respectively. A two week interval separated the two brushing sessions. Traumatic lesions of the attached gingiva were stained with a disclosing solution, photographed and evaluated planimetrically. The "cut bristles" caused gingival abrasions 30% greater in extent than the round end bristles. The difference was not due to single brushing strokes accidentally greater for the "cut bristles". The size of the lesions was not sex dependent. To prevent gingival damage it is desirable to either round the bristles in production or to rid the bristle ends at least of sharp edges.