[Histological changes in periodontal tissues of rat molars following perforation of the pulp and its floor].

Histological changes in periodontal tissues of the first maxillary molars of immature rats following perforation down through the floor of pulp chamber were observed with light and electron microscopes. One and two weeks after perforation, ovally shaped epithelial islands were frequently observed in the apical end of the roots. Cellular cementum was being formed rapidly around the islands and the amorphous layer, containing scanty collagen fibrils and microfilaments, was observed between the epithelial islands and cementum. Four and eight weeks after the treatment, the islands were embedded in the cellular cementum and undergoing degeneration. In the bifurcational area, destruction of the periodontal tissues and subsequent proliferation of epithelium derived from the gingiva were observed. The epithelial rests of Malassez were characterized by enlargement of nucleus and cytoplasm. The results indicate that inflammatory stimulation induced histological changes of the odontogenic epithelial cells and enhances the formation of cementum. The possibility that the epithelial cells are associated with the formation of cementum is also suggested.