Physiologic changes of the periodontal tissues and molars in the adult rat

1. The rat molar has been used in experimental studies because of fair comparison with the permanent human tooth. The purpose of the present investigation was to examine precisely the physiologic tooth movement and periodontal age changes of the rat molar.2. It was concluded that the molars had showed gradual vertical eruption to compensate for attrition, and repeating continuous medio-lingual tipping probably due to influence on occlusal function. It was conjectured that the medio-lingual tipping was constantly behaved at the top of the alveolar crest and intraradicular septum, and the movement was most remarkable at the area of the first molar.3. There was slight gingival inflammation remained rather constant in all aged animals. The inflammatory changes, however, limited to the superficial regions of gingivae, and there was no case of which changes extended to deep regions such as periodontal ligament and alveolar bone.4. The pattern of apposition and resorption of bone on the alveolar walls was characteristic for the physiologic tooth movement. Available evidence indicated that the bony apposition was remarkable on the medio-lingual walls and bony resorption on the disto-buccal one, except for the mesial wall of the mesial root of the first molar.5. Functional arrangement of the periodontal ligament was well preserved throughout all aged animals showing normal mastication.6. It was reasonable to presume that the appositional pattern of growth of cellular cementum was related to the fact of the physiologic tooth movement. And the increase in width of the fibrous cementum was affected by tension and quantity of the periodontal ligaments.