Remodelling of the periodontal ligament during eruption of the rat incisor

Abstract

OBSERVATIONS on the healing of a wound involving the alveolar process, periodontal ligament and cementum of the continuously erupting rat incisor have cast light on the changes that take place in the periodontal ligament as the tooth erupts. Details of the experimental and histological procedures have already been described (MELCHER, 1967). Transverse sections of the mandible were cut. In the experimental area the fibres of the periodontal ligament between cementum and bone were stained pink by van Gieson’s picro-fuchsin, were black or brown when impregnated with silver and were arranged in two ways. On the tooth side, they formed a feltwork and were embedded in cementum. Intermingling and apparently continuous with these, but embedded in bone, were fibres gathered in tufts (Fig. 2). The tufts were predominantly brown in silver-impregnated sections and enclosed connective tissue cells and vessels. The wound destroyed an area of alveolar bone, periodontal ligament, cementum and dentine. Eruption of the incisor during the first four days of healing resulted in the damaged area of the tooth coming to lie partly in the wound and partly anterior to the wound (Fig. 1). As a result, there was an area anterior to the wound where the tooth was damaged but the bone intact. Here, the fibre-tufts on the bone side of the periodontal ligament were not noticeably disorganized (Fig. 3). However, on the other side of the ligament, opposite the defect in the tooth, the fibres, although stained pink by the van Gieson method, were disorganized and were associated with numerous fibroblasts exhibiting a high cytoplasm-to-nucleus ratio, a vesicular nucleus and haemateinophilic cytoplasm. Some loose, randomly arranged, pink fibres and fibroblasts were also present in the dentine defect. By contrast, there was an area in the posterior part of the defect where the bone was missing but the tooth was intact (Figs. 1 and 4). Here, apparently organized periodontal fibres embedded in cementum radiated out into the bone wound. At their periphery disorganized fibres were present together with numerous fibroblasts similar to those described above, many of which appeared to be invading the adjacent haematoma. No tufts of brown collagen fibres were seen. It seems apparent from these observations that the ordered fibres of the ligament anterior to the bone wound were those that were originally attached to the alveolar bone, and that they could not have been carried forward from the wound, where both