[Study of the relationship between fibronectin and morphological changes in the early process of periodontal ligament formation].

The localization of fibronectin (FN) in the initial stage of periodontal ligament formation was examined immunohistochemically. This period was divided into four stages with respect to epithelial-mesenchymal interactions. FN was observed on the cell membrane of the follicular mesenchymal cells near the basement membrane of the epithelial root sheath outer layer (stage I). In the stages of contact between follicular mesenchymal cells and the epithelial cells of the outer layer (stage II) and those penetrating the intercellular space of the discontinuous epithelial cells of the root sheath (stage III), FN was observed on the cell membrane of follicular mesenchymal cells which was in contact with epithelial cells. Follicular mesenchymal cells which were in contact with the FN rich dentin surface had well-developed cytoplasmic organelles (stage IV). Nonstriated fibrils were seen close to the projection of mesenchymal cells elongating toward the dentin surface, and were oriented parallel to the projection. FN in the small fibrils was clearly observed in the area connected to the mesenchymal cells. The reaction of FN was less in the area where collagen fibrils were organized into bundles. A dense amount of FN was seen where the periodontal ligament crossed into the dentin surface collagen. It is considered that FN plays an important role in follicular mesenchymal cell penetration of the increasing intercellular space between epithelial cells, the differentiation into the fibroblast at the dentin surface, the formation and arrangement of the periodontal ligament, and the attachment of the periodontal ligament to the dentin surface.