In vitro measurement of orthodontic tooth movement in rats given beta-aminopropionitrile or hydrocortisone using a time-lapse videotape recorder.

In vitro tooth movement of rat molars in response to an orthodontic force was recorded using a time-lapse videotape recorder and analysed by a computer system. Rats received daily s.c. injections of beta-aminopropionitrile (BAPN, 300 mg/kg/day) or hydrocortisone (10 mg/kg/day) for a period of 7 days. After drug administration, the animals were killed and the mandibles dissected. The jaw was then held under a stereomicroscope with a haemostatic clamp and an elastic band was inserted between the first and second molars. The movements of reference points on the occlusal surfaces of the first and second molars were recorded for 20 hours using a time-lapse videotape recorder. Mesiolingual movement of the first molar and distobuccal movement of the second molar were observed. During the experimental period, the greatest amount of total tooth movement in the first and second molars was seen in the group pretreated with BAPN, less movement was observed in the control group, and the group pretreated with hydrocortisone exhibited the least amount of movement. The highest rates of tooth movement were observed during the initial hour in each of the groups, and decreased thereafter. The initial rates of movement were also greatest in the BAPN group, less in the control group, and least in the hydrocortisone group. These results indicate that treatment with BAPN accelerated experimental tooth movements in vitro and hydrocortisone treatment inhibited the movements, suggesting that, although a part of the tooth movement measured in this experiment was due to deformation of the alveolar bone, the mechanical properties of the periodontal ligament play an important role in the regulation of orthodontic tooth movement.