Some effects of chlorhexidine on the plaque flora of the beagle dog.

Abstract

Three series of experiments were performed during which Beagle dogs were given a plaque forming diet, in Series I 10 dogs were sprayed twice daily with 0.2 per cent chlorhexidine and 10 controls with saline for six months. In Series II the same treatment was used for 18 months in 16 dogs (8 treated. 8 controls). In Series III, comprising three dogs, the teeth of the left jaws, were subjected to two different concentrations of chlorhexidine for 5 + 5 weeks (2 resp. 0.1 %) while the teeth of the right jaws received saline treatment. During a subsequent period of 3 months all teeth were created with saline.Dental plaque was sampled at the end of the three experimental periods, in Series III also one, three, six and thirteen weeks later. The sensitivity to chlorhexidine of the plaque bacteria was tested using a modification of “the paper disc method”. In all series the plaque bacteria from chlorhexidine treated teeth displayed reduced sensitivity to the drug. After termination of the chlorhexidine treatment in the Series III‐experiments the reduced sensivity to chlorhexidine of plaque bacteria from chlorhexidine treated teeth slowly approached the corresponding values from saline treated teeth.Plaque samples taken after 18 months (Series II) were studied by means of a dilution‐plate method. The‐ dominating colonies from each plate were identified as gram‐negative aerobic rods. Most of the bacteria from chlorhexidine treated dogs grew on trypticase soy agar plates containing 320 μg/ml chlorhexidine. while bacteria from the saline treated animals only grew on plates containing 20 μg/ml.