Age Changes in the Periodontal Tissues of the Rat Molar

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Abstract
This quantitative study was based on histologic examination of 74 normal Wistar albino and 21 Norwegian gray rats 21-1000 days of age. In both strains the downgrowth of the epithelial attachment progressed with age, and the incidence of papillary gingivitis tended to increase with age. Thd distance between the alveolar crest and the cemento-enamel junction increased with the continuous eruption of the molar teeth. Instances of bone resorption at the alveolar crest did not occur until 700 days of age. Apposition of bone at the alveolar crest was seen even as late as 900 days of age. The width of the interdental septum decreased to about 1/3, largely by resorption along its mesial wall. In the older animals the root surfaces of adjacent teeth tended to approximate, leading to the perforation of the interdental septum and resorption of the roots. Pocket formation in the rat was not commonly seen. The Norwegian gray rat showed greater decrease in width of the interdental septum and a higher incidence of root resorption with age than did the albino rat. Differences in the amt., character and morph. of the cementum of the 2 strains indicated greater activity of cementoblasts in the albino strain. The significant differences noted in the 2 strains of animals emphasize the importance in experimental work of giving consideration to possible inherent differences in various strains of the same spp. This study also aids in evaluating the results of exptl. studies in the molars of rats of different ages.