Ultrastructure of odontoblasts in kitten tooth germs as revealed by freeze-fracture

Fifteen kittens were perfused with 2.5 per cent glutaraldehyde or modified Karnovsky fixative. Distribution and structural features of the three kinds of intercellular junctions: gap junctions, macular tight junctions and desmosome-like junctions were clarified by correlated observations using thin sections and freeze-fracture replicas. Distal junctional complexes of the odontoblasts were composed of both gap and macular tight junctions and sealed extracellular spaces incompletely, because of the poor sealing capacities of macular tight junctions. Therefore, there was no predentine-pulp barrier in the odontoblast layer. Except for the junctional complex, no tight junction was observed in the odontoblasts. Gap junctions and desmosome-like junctions were found between adjacent odontoblasts and between odontoblasts and neighbouring pulp cells. Gap junctions were similar to those of many other tissues but the desmosome-like junctions were different from mature desmosomes in the epithelial cells and showed immature features. Each intercellular junction of odontoblasts is considered to form a site of intercellular communication and cell-to-cell attachment.