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The regenerating process in tissue around periodontally diseased teeth (PDTs) and non-diseased teeth (NDTs) was studied with clinical and histological analysis following flap surgery. PDTs were prepared in the premolars of 7 beagle dogs by which surgically denuding the root surfaces by removing the alveolar bone. The denuded sites were covered with gutta-percha plates and gingival epithelial tissues and exposed to the oral environment for 4 weeks. Then flap surgery was performed on the PDTs. As control sites, the root surfaces of the NDTs were denuded by removing the alveolar bone at the time of flap surgery. The root surfaces of the PDTs and NDTs were planed with curette scalers at one root site but not at the other site. Clinical and histopathological findings were evaluated at fixed intervals for 32 weeks after surgery. Results of observation were as follows. 1. In the clinical evaluations, the gingival inflammation index, probing depth and attachment level were improved in the root planing (PR) group of both the PDTs and the NDTs, but in the non RP group of PDTs there was no improvement. 2. In the histologic observation, the position of the gingival margin, length of regenerated junctional epithelium, depth of gingival sulcus and the level of connective tissue attachment in the RP groups recovered in both the PDTs and the NDTs but not in the non RP groups.

In an attempt to promote periodontal tissue regeneration following periodontal surgery, an experimental study was conducted by applying the guided tissue regeneration (GTR) technique to a cross-linked atelocollagen membrane. The palatal gingiva of maxillary first molars of rats were dissected and the cementum was removed by curettage. An atelocollagen membrane was implanted into the site of dissection in the experimental group, while the control group received no implant. The wound healing processes in two groups were examined by histopathological methods, including histometric analysis of the cells and histological measurement of the regenerated periodontal tissue, 1, 3, 5, 7, 14 and 21 days, and 1, 2, 3 and 4 months after the implantation. The results were as follows. 1) Implantation of the atelocollagen membrane did not enhance or prolong the inflammatory reaction, indicating possible involvement of inflammatory cells and macrophages in the membrane absorption. 2) In the experimental group, epithelial downgrowth was markedly inhibited and fiber bundles of the gingival connective tissue were clearly arranged vertical to the root surface. 3) The experimental group showed a significant increase in new cementum formation 2 months after surgery compared with the control group. Root resorption was seldom observed in either group during the study period. The above results indicate that the GTR technique using an atelocollagen membrane may provide an effective method to promote periodontal tissue regeneration after periodontal surgery.