[Changes in the microvascular pattern of the periodontal ligament in an experimental tooth extrusion]

Forty eight adult cats were employed to investigate the serial changes of vascular patterns of the periodontal ligament on tooth extrusion. The right upper canines have been successively extruded (initial load 40 gr) with a open coil spring. The experimental periods were set on 1, 2, 3, 4 and 6 weeks respectively. On each experimental period, the microvascular casts of the periodontal ligament and alveolar bone around the experimental tooth were prepared for the scanning electron microscopy, utilizing the acrylic plastic injection method (Taniguchi and Ohta, et al. 1952 and 1955). And the serial sections of the surrounding tissues of the experimental tooth were made. In order to elucidate the mode of the tooth movement, the load of applied force and the distance of extrusion were measured. Results obtained were as follows: 1. The experimental tooth was extruded rapidly during first two weeks. The speed reduced gradually afterwards. 2. The new vascularization was seen around the apex first, then widely spread in the periodontal ligament. And the remarkable trabecula-shaped bone formation were observed around the venous networks of the root apex after two week period. 3. The tissue reactions after the tooth extrusion delayed in comparison with the movement of the tooth. 4. Although the tissue reactions of the root apex of the extruded tooth were originally similar to the one in the transverse tooth movement, slight differences were found in timing of the tissue change and shape of the capillary network. The findings of the tissue change showed that the light force was indicated in extrusion of the tooth. And the range of action of the force applied should be limited in orthodontic clinic.