Immunohistochemical study of the relationship between extracellular matrix and root bifurcation in the mouse molar

In order to investigate epithelial-mesenchymal interaction during root bifurcation, the distribution of type III and I collagen, fibronectin and laminin in the epithelial-mesenchymal junction between the dental epithelia (epithelial diaphragm and interradicular process) and the cells of the dental papilla (or pre-odontoblasts) was examined, using maxillary first molar tooth germs of CF1 mice from day 1-16 after birth. Three-dimensional reconstructions of the immunofluorescent patterns were made from serial sections of tooth germs from day 3-9, stained with the antibodies against the collagens. The findings were as follows. (1) Type III collagen was first seen in the epithelial-mesenchymal junction at the tip of the interradicular process, where it sprouted from the epithelial diaphragm, and spread along the interradicular process toward its base, accompanied its extension, and then disappeared on completion of root bifurcation. No staining was seen in the epithelial-mesenchymal junction at the epithelial diaphragm during and after root bifurcation. (2) Type I collagen appeared in the epithelial-mesenchymal junction at the base of the interradicular process, where it sprouted from the epithelial diaphragm and spread toward the tip of the interradicular process, following its extension, and increased on completion of the root bifurcation. No staining was seen in the epithelial-mesenchymal junction at the epithelial diaphragm during or after root bifurcation. (3) Fibronectin and laminin remained constant in the epithelial-mesenchymal junction, both at the interradicular process and the epithelial diaphragm, during and after root bifurcation. These findings suggest that type III collagen may play a significant role in the early stage of root bifurcation in the molar.