The aim of this experiment was to study clinical parameters when 3 different frequencies of plaque removal were applied to healthy gingivae in the beagle dog model. The maxillary first, second and third premolars of 12 beagle dogs, at the start of the experiment 2 years of age, were, after a thorough cleaning, submitted to daily plaque removal during a pre-experimental period of 8 weeks. At the start of the experiment, the dogs were distributed into 3 groups of 4 dogs each: one group was brushed 7 times a week, a second group was brushed 3 times a week and another group was brushed only once a week. Brushing was executed over a period of 24 weeks, on the right sides of the upper jaws. The left upper jaws served as controls. At regular intervals, the plaque index, the gingival index and probing depths were assessed. A "brushing effect" was calculated for each dog, to include information on all within-dog and between dog variations. Comparison of brushing effects revealed that in this experimental model, plaque removal with a frequency of 3 times a week was sufficient to preserve gingival health, whereas tooth brushing once a week resulted in gingival inflammation. Therefore it can be concluded that 3 times a week is the critical brushing frequency in the beagle dog model with healthy gingiva at baseline.