Epithelial-Mesenchymal Junctional Area in an Early Stage of Odontogenesis in Macaca Fuscata

Abstract

The epithelial-mesenchymal junctional area in tooth germs of one- and three-year-old Japanese monkeys was studied with electron microscopy.The plasma membranes at the distal ends of inner enamel epithelium cells were relatively even, and were associated with basement membrane. A large number of filaments, which were 15 nm in diameter and up to 2 μm in length, were present, extending perpendicularly from the basement membrane toward the dental papilla, forming an unique fibrillar layer. The distal cytoplasm of the cell contained rather few vesicles and granules which were positive for the acid phosphatase reaction. The distal ends of differentiating ameloblasts showed irregular undulations and numerous small processes which penetrated through the basement membrane and fibrillar layer. Following an increase of the undulations, the fibrillar layer and the basement membrane were engulfed by the cells and removed from the surface of pre-dentin. Large irregular bodies, which were filled with the filaments of the disintegrating fibrillar layer, were observed frequently. The distal cytoplasm contained a large number of coated pits, coated vesicles, and acid-phosphatase-positive granules. The fibrillar layer then disappeared, being replaced by collagen fibrils in the pre-dentin, which was in the stage of early mineralization.These results indicate that the fibrillar layer is removed by the differentiating ameloblasts and degraded through an engulfing system which is formed by the cell surfaces.