Ultrastructure of the relationship between odontoblast processes and nerve fibres in dentinal tubules of rat molar teeth.

Serial ultra-thin sections across tubules were analysed three-dimensionally. There was no difficulty in distinguishing nerve fibres and odontoblast processes. In many tubules, a bundle of naked nerve fibres accompanied the odontoblast process for up to 50 microns located in concavities of the surface of the process (type I relationship). No specialized membrane structures between the plasma membrane of nerves and odontoblast process, such as gap junction or membrane thickening similar to that of synapse, were encountered. In a few tubules, the lamellar cytoplasmic processes of the odontoblast extensively enveloped the terminal part of the nerve fibres (type II relationship). This pattern was found in an animal older than the others in which there were lucent tubules and perhaps arose from peripheral sensory stimuli.