Morphological studies on the reparative process of the extraction wound have been carried out by many investigators, but the cell level scanning electron microscopic morphological investigation remains unclarified. In the present study, the healing processes of tooth extraction wounds in rats were observed histologically, roentgenologically and scanning electron microscopically. The results obtained were as follows : 1. The extraction wound healing process is divided into four stages in general : blood clot stage, granulation stage, bone trabeculae stage and bone reconstruction stage. But there were no clear borderlines between these stage ; in an extraction socket plural healing stages could be observed concurrently. 2. Prevention of infection in extraction wound was as follows : a number of inflammatory cells, especially polymorphonuclear leucocytes (PMNL), diffused in the blood clot in early stage and the PMNL then gradually localized in the upper part of the blood clot. When the gingival epithelium filled the edentulous area, almost all of inflammatory cells disappeared. 3. Fibroblasts and collagen fibers proliferated from the socket wall, osteoblasts and new bone trabeculae arose from the fundus of the socket. These findings suggest that the start of healing is not in gingival periosteum but in periodontium. 4. Scanning electron microscopy showed the transform steps to formation of connective tissue in the extraction wound. In the early stage, blood clot and fibrins occupied the extraction socket. As time went by, fibroblasts proliferated from the socket wall and collagen fibers were formed. The collagen fibers and capillaries increased in number and entered the blood clot. At the same time osteoblasts proliferated in the fundus of the socket. Then, the bone trabeculae and new bone formation were observed. 5. By scanning electron microscopy, a large number of macrophages were observed at 12 hr after extraction and then decreased daily. At the same time the number of osteoclasts began to increase. Three days after extraction, the number of osteoclasts reached its maximum. Numerous bone resorbed lacunae were observed. The possibilities that osteoclasts are derived by fusion of macrophages and that not only osteoclasts but also macrophages participate in the bone resorption were discussed.
