Dental sensory receptor structure in human teeth.

Electron microscopy was used to study normal human extracted teeth in order to define the junctions between sensory nerve endings and other cells in external pulp and inner dentin at the crown tip. Two sets of associated cells were found: (1) Connective tissue cells. The pulpal fibroblast newtork made occasional desmosome junctions with the odontoblast newtork, and the cells of each network formed many gap junctions and desmosomes with one another. (2) Nerve endings. The terminal axons formed a succession of appositions with each other or with Schwann cells in the plexus of Raschkow and the cell-free zone, possibly with fibroblasts in the cell-free zone and odontoblast layer, and with odontoblasts in the odontoblast layer, predentin and dentin. The appositions between nerve endings and their companion cells at all levels usually maintained a regular intercellular spacing of at least 15-20 nm. In predentin and dentin, axons could be easily identified by their distinctive vesicles and mitochondria, and they often occurred within clusters of adjacent dentinal tubules; in the odontoblast layer axon identification was much more difficult. Axo-axonic appositions were found in the plexus of Raschkow, the cell-free zone, predentin and dentin; in many cases, bare axons were separated from each other only by a 5-10 nm extracellular space. Dental sensory mechanisms are discussed in relation to these observations.