Abstract
The effects of loss and restoration of occlusal function on periodontal tissues were investigated using rats as a model system. In the occlusal loss group, the left maxillary molars were reduced by cutting the crowns to produce loss of occlusion. In the occlusal restoration group, dental restoration was performed on the crown of the molars 21 days after cutting. Untreated normal rats were used as the control group. In all three groups, the periodontal tissues of the first molar on the left mandible were routinely prepared for histopathological and histometrical analysis.
Rapid atrophic change was seen in the periodontal ligament due to the loss of occlusal function, and almost total loss of the functional arrangement of the periodontal ligament was observed 2-3 days after cutting the crown. At 4-5 days after cutting, new bone formation on the alveolar surface narrowed the periodontal space to about half that of the control animals. At 21 days after cutting most normal functional structures of the tissues had been lost. In the restoration group, bone resorption due to an increased number of osteoclasts was observed 1-2, days after restoration. The bone resorption tendeci to advance from the bone marrow side toward the periodontal ligament side, and the width of the periodontal space was seen to increase slowly. The number of fibroblasts increased and regeneration of fibers in the periodontal ligament occurred soon after the crown was restored. The process of periodontal ligament regeneration after recovery of occlusal function was relatively slow, but by 28 days most of the functional structures in the periodontal tissues had been restored. Thus, the periodontal tissues responded rapidly to the changes in occlusal functions. The different activities of fibroblasts, osteoblasts, osteoclasts and cementblasts during changes in occlusal functions were observed, and each cell type appeared to play an important specific role during the occlusal loss and restoration processes.
