[Ultrastructural study of bone cells and matrix incident in experimental periodontitis]

The purpose of this study was to examine the process of bone destruction and also to examine the ultrastructural features of the cells and the resorbed sites of bone matrix in experimental periodontitis. To induce the periodontitis, a defect was prepared with a endodontic reamer in the proximal surfaces of the upper 1st and 2nd molars of rats. The process of the bone resorption was examined histopathologically once a week for 3 weeks. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to examine the cells and the bone matrix using the specimens taken 2 or 3 weeks after the start of the experiment. The alveolar bone resorptions of interdental areas were observed 2 weeks after starting the experiment and it continued to progress longitudinally. After 3 weeks, concave bone loss appeared on the buccal surfaces of the bone. The resorbed bone surface revealed by TEM typical osteoclasts, macrophages and mononuclear cells resorbing collagen fibrils. These cells resorbing collagen fibrils which worked with the osteoclasts appeared frequently in resorbed sites. Numerous osteoblasts appeared on the resorbed area. However, judging from their undeveloped organelles, their function seemed to remain inactive and unproductive. SEM showed many resorbed lacunae in the alveolar bone in interdental areas and the differences in the ultrastructural features of the resorption lacunae were distinctive. These findings suggest that the massive and rapid bone resorption in experimental periodontitis is the result of increased osteoclastic activity and depressed osteoblastic activity. The different ultrastructural features of each lacunae were results of the resorbing stage.