Analysis of tooth movement into an extraction space in the rat

The purpose of this study was to evaluate the amplitude, direction and nature (translation or rotation) of the movements of teeth bordering an extraction site. Two experimental approaches were used. In one series of experiments, second maxillary molars were removed in 10 anaesthetized rats. To allow precise measurements of tooth movement into the extraction space, small cavities were drilled in the proximal surfaces of the first and third molars facing the gap. An elastomer impression was taken and the distance between the two cavities was recorded. This measurement was repeated 1, 2 and 3 months later. After killing the rats, the skulls were dried. The direction of movement was observed on occlusal photographs, and lateral X-rays were used to evaluate the nature of the drift (translation or rotation) observed. To evaluate the impact of occlusal forces on the tooth movements, a second experimental system was used in which the antagonistic occlusal contacts on the test side were removed (12 rats). In the first experiments, the average reduction of the extraction gap was 40.7 +/- 1.8% of the initial value, and in the second experiment, 44.7 +/- 3.3%. In both experimental systems the movement was derived largely from a mesial drift of the third molar, and its rate decreased with time. Furthermore, the drift of the third molar comprised one-third rotation and two-thirds translation. Student's t-test showed no influence of occlusal forces on the tooth movements.