[Histopathological study on qualitative changes in gingival collagen fibers for experimental periodontitis in rats. Remodeling of type I and III collagens detected by the Picrosirius-polarization method].

The objective of this study was to demonstrate the movement of type I and III collagens accompanying gingival inflammatory destruction. Experimental marginal periodontitis was induced by a calculogenic diet and a high-sucrose diet with feces in 3-week-old Wistar rats. We observed the changes in the interdental periodontium histopathologically by using the picrosirius-polarization method and an electron microscope. 1. After 5 weeks of eating the calculogenic diet, mild gingivitis was found. A small number of inflammatory cells consisting of neutrophils were seen. At the 2nd week, a variety of bone resorptions of alveolar crests began to appear. At the 10th week, an epithelial downgrowth was observed. At the 64th week, migration of epithelial attachment to half of the apex and a high degree of inflammatory cell infiltration of plasma cells could be seen. 2. Observations under the polarization microscope showed that interdantal horizontal fibers became coarse and type I collagen decreased but at the middle type III increased. However when the horizontal fasciculus were newly formed, type I was always dominant. Between interdental horizontal fibers and the alveolar crest, type III was increased. 3. Under the electron microscope microfibrils were found around adjacent degraded fibroblasts at the locations where collagen fibrils were destroyed and disappeared. In contrast, at the locations detached from inflammatory cell infiltration small bundles of microfibrils were seen. It is suggested that at the areas of destructive collagen structures the relative increase in type III and the appearance of microfibrils were caused by the reduction of type I. At the same time at the sites of detachment from the lesions, complete growth of type III and the appearance of microfibrils were found and were considered to be newly formed juvenile collagen structures. Moreover it is concluded that a balance proceeds with the qualitative changes in the types of collagen fibers involving breakdown and new formation.