Biometric analyis of tooth migration after approximal contact removal in the rat

Nineteen 8-week-old female Sprague-Dawley rats were used to observe macroscopically the direction of tooth movements following removal of approximal contacts. In 10 rats, under anaesthesia, approximal contact between the second and third right maxillary molars (M2–M3) was removed by grinding. These animals and a control group of nine rats were housed with normal diet and water ad libitum for 7 weeks. After killing, the skulls of all animals wre removed, dried, and fixed in a standardized position on a Horsley-Clarke type stereotaxic frame. Using a micromanipulator graduated to 1/100 mm and mobile in three orthogonal directions, distances between the teeth (M1 or M3) and some bone structures that served as landmarks were measured. These measurements showed the direction of tooth movements in the experimental approximal space. After statistical analysis of the data, the results showed that the approximal space between M2 and M3 was closed by both a distal drift of M1-M2 and a mesial migration of M3. It was concluded that, in the rat, a mesial drift exists that can be induced by the loss of approximal contact. This movement is distinct from the distal physiological dental migration classically described in histological studies.