[Electron microscopic study on the tissue reaction after root canal filling following artificial periapical lesions--about periapical lesions induced by carrageenin].

Although a number of reports on the formation of periapical lesions have been down, little study on the healing stage of this one is seen. Therefore, the aim of this study was to investigate the changes of the fine structure of the healing stage of the artificial periapical lesions after root canal filling and to make an experimental model for the further screening test of various kinds of medicaments and materials for root canal treatment and root canal filling. In this study, the first mandibular molars of male Wistar strain rats were used. Periapical lesions were induced by 0.5% carrageenin and after three weeks, the root canals of the first molars were filled with gutta-percha points and sealers. Then, the healing stage of the periapical lesion was observed light microscopically, electron-microscopically and enzyme (alkaline phosphatase, ALP, and acid phosphatase, ACP)-histochemically. The results were as follows after the root canal filling with carrageenins: 1. At 1 to 7 days, a great number of neutrophils and histiocytes were observed and expansion of periapical lesions caused by the irritation followed by root canal filling was observed. 2. At 2 to 3 weeks, a great number of leukocytes, histiocytes and fibroblasts were observed in the vicinity of the root apex. 3. At 4 to 5 weeks, a great number of histiocytes and mast cells were observed and granulated tissues of the periapical lesions had a tendency to become fibrosis and new calcified cement increased at the root apex. 4. At 7 to 10 weeks, the fibroblast granulation tissue around the periapical lesions synthesized active collagen fibers and the deposition of new alveolar bone was seen within the resorbed alveolar bone. 5. At 15 to 20 weeks, the periapical lesions could be thought to be healing histopathologically although some of inflammatory cells were seen 20 weeks after treatment. 6. At 10 weeks, strong positive responses of ALP were recognized. At 20 weeks, the general appearance of both the ALP and ACP staining showed almost the same response as that of normal periodontium. 7. As for the prognosis, "over filling" showed better healing than that of "under filling". 8. In the case which the root apex was fractured, inflammation lasted for a long period.