The purpose of the investigation was to present an experimental model for a comparative histological evaluation of the effect on gingiva using two different types of bristle material at tooth brushing. Fifteen dogs constituted the material. Two different teeth or groups of teeth were selected on each dog. One tooths was brushed with a nylon brush. The diameter of the bristles was approximately 0.25 mm. The other tooth was brushed with a polytene brush. The diameter of the bristles vary between 0.7 mm at the base of the bristle to 0.25 mm in the near end of the bristle. Manual brushing during 10—60 seconds was carried out in 7 dogs and the other eight dogs were brushed with a mechanical device for 10—30 seconds. A histological evaluation of the relative degree of tissue damages based upon a grading of these damages in terms of a 0—3 point scale was carried out by two independent observers. Wilcoxon's matched-pair signed rank test was applied for a statistical analysis of the result of the histological examination. The conclusion was that the two different types of brushes most likely cause different damages on the gingival tissue and that the polytene brush appeared to cause less tissue damage than the nylon brush.