AGE CHANGES IN THE PERIODONTAL TISSUES OF THE RAT MOLAR

¹ Dental Service of the Outpatient Treatment Department, Veterans Administration Regional Office, and the Department of Histology and Oral Pathology, University of Illinois College of Dentistry, Chicago, Ill.

This quantitative study of the age changes in the supporting tissues of the rat molar was based on histologic examination of seventy-four normal Wistar albino and twenty-one Norwegian gray rats 21 to 1,000 days of age.

Tabulation of the data included the level of the epithelial attachment, degree of gingival inflammation, position of the alveolar crest in relation to the cemento-enamel junction, state of cellular activity, and pattern of apposition at the alveolar crest, width of the interdental septum, distance of the cellular cementum from the cemento-enamel junction, and amount of root resorption.

The findings may be summarized as follows:

Age Changes in the Wistar Albino Strain 21 to 1,000 Days of Age

1. Downgrowth of the epithelial attachment progressed as the age of the animal increased, so that at 21 days of age 100 per cent of the epithelial attachments were found only on the enamel (Stage 1), and at 1,000 days of age 75 per cent of the epithelial attachments were found only on the cementum (Stage 4).

2. Downgrowth of the epithelial attachment occurred earlier and progressed farther on the mesial of each molar tooth than on the distal.

3. The incidence of gingival inflammation was lower in the gingival papillae mesial to the first molar and distal to the third molar than in the papillae located between the molar teeth.

4. The incidence of papillary gingivitis tended to increase with age.

5. The distance between the alveolar crest and the cemento-enamel junction increased with age. The rate of increase in distance between these two points diminished as age advanced, indicating a slowing of the growth and eruption process with age.

6. Bone apposition occurred at the alveolar crest between 21 and 900 days of age. Bone resorption occasionally was seen at the alveolar crest in the very old animals.

7. The appositional pattern at the crest of the interdental septa can be ascertained from the resting lines. They slant distally and apically. Thus, the height of the functional part of the septum serving tooth attachment is greater on the mesial than on the distal.

8. Width of the interdental septum between the most prominent parts of the approximating roots decreased from 50 to 1,000 days of age, about 32 per cent by resorption, largely along its mesial wall, causing slitlike defects, or a perforation of the septum.

9. The position of the coronal end of the cellular cementum did not change between 50 and 1,000 days of age.

10. Root resorption occurred most commonly on approximating root surfaces of adjacent teeth, and the number of areas of resorption tended to increase as the age of the animal increased.