The aims of the present study were: (1) to establish the incidence of gingival abrasion as a result of toothbrushing, using a manual and electric toothbrush; (2) to establish the influence of filament end-rounding on the incidence of gingival abrasion and the efficacy of toothbrushing; (3) to assess whether the speed of the electric brush has a feedback-effect on the brushing force used and to correlate the incidence of gingival abrasion with force. 2 experiments were carried out. In the first experiment, 50 subjects brushed for 3 weeks every other day with either a manual (Butler 411) or an electric toothbrush (Braun/Oral-B Ultra Plaque Remover-D9). All received brief instructions and were asked to abstain from oral hygiene 24 hrs before their appointment. After disclosing the teeth and gums with Mira-2-Tone solution, plaque and gingival abrasion were assessed. Next, the panelists brushed in a random split-mouth order. After brushing and a second disclosing, plaque and abrasion were re-assessed. The results showed that the incidence of gingival abrasion was comparable for the manual and the D9. Using a similar design as in experiment no. 1, in experiment no. 2 a new group of 47 subjects brushed for 3 weeks alternating between the Braun/Oral-B Plaque Remover-D7 and D9. At the appointment, the subjects first brushed in a split-mouth order with the D9 with 2 different types of endrounding. Plaque and abrasion were assessed. Immediately following this brushing exercise, the subjects re-brushed with the D7 (2800 rot/min) and the D9 (3600 rot/min) during which brushing force was measured. The results of this experiment showed that endrounding has no effect on plaque removal but does effect the incidence of gingival abrasion. Brushing force is not influenced by the speed of the brushhead and no correlation with the incidence of gingival abrasion was observed. In conclusion, the results of this study show that gingival abrasion is not influenced by brushing force, but is affected by filament endrounding.