Loss of connective tissue attachment in the marginal periodontium of the mouse following blockage of eruption

Following blockage of eruption of continuously erupting teeth in rodents, regressive changes occur in the marginal periodontium resulting in detachment of periodontal ligament from the root surface and concomitant apical migration of the functional epithelium. In the present investigation we attempted to identify the mechanisms that are possibly responsible for these changes which occur in the absence of dental plaque. Mice were killed at time intervals varying from one hour up to nine months following pinning their lower right incisor to the surrounding alveolar bone. Stereologic analysis of ultrathin sections revealed that, on the pinned side, the collagen content of the periodontal ligament adjacent to the apical termination of the functional epithelium was substantially less as compared with the ligament at more apical levels. The low volume density of collagen close to the functional epithelium was accompanied by a relatively high amount of phagocytosed collagen in fibroblasts. The volume density of collagen‐containing vacuoles in these cells correlated well with the rate at which the periodontal ligament was detached from the tooth, thereby suggesting that collagen degradation in this area is likely to be performed by connective tissue cells. In addition, it was observed that layers of afibrillar cementum were deposited against the root surface. This would seam to suggest a local disturbance in the incorporation of periodontal ligament fibers in the cementum and could possibly facilitate therapid apical progression of the junctional epithelium during the course of the experiment.