Two complementary methods of assessing periodontal bone level in rats.

Several methods have been applied to measure periodontal disease in rats. The purpose of the present study was to test the reproducibility of a morphometric and a radiographic method and to describe the correlation between the two methods. Periodontal bone loss on 25 defleshed rat heads was assessed under microscopic by measuring the distances from the cementoenamel junction to the alveolar bone crest at 36 buccal sites in each animal. On magnified radiographs from 25 rat mandibles periodontal bone support was expressed by the ratio apex-deepest bony defect: apex-cusp tip distally on first molars. All measurements were performed blind and in duplicate on two separate occasions. The bilateral 95% confidence limits for the error of method of measurement were estimated from the t-distribution. In a second experiment 50 rat heads were assessed by both methods, and the correlation between the recordings was estimated by the Spearman rank correlation analysis. Compared to the considerable total variation in the material, the variations due to error of methods of measurement were small, i.e. the reproducibility of both methods was satisfactory. A significant correlation was found between the methods. Since the morphometric method mainly measures horizontal bone loss, whereas the radiographic method detects intrabony interproximal defects, it is concluded that future studies would benefit from applying both methods to assess alveolar bone loss in rats.