Neuro-Odontoblast Relationships

Objective: To study the close relationship between odontoblasts and intradental nerves in order to elucidate its role in the sensory mechanism that is responsible for dentinal pain. Methods: Jaws dissected from 40 mice and 35 rats, and 24 human molar teeth, were routinely embedded into paraffin or araldite®. Following embedding, the specimens were studied using immunohistochemistry for some common neuronal and neuropeptide markers or electron microscopy. Results: Strong immunoreactivity for synaptophysin reveals the presence of presynaptic vesicles in the odontoblast zone of the pulp. Immunoreactivity for nerve growth factor receptor (NGFR) shows clearly that the neurites enter the dentinal tubules together with the odontoblast processes as they share a similar course. Electron microscopy images of the neuro-odontoblast relationship demonstrate some morphological characteristics such as synapse-like contacts between neurites and odontoblast processes, the presence of numerous small granular vesicles (SGV) and some clear cored vesicles in the odontoblast process at the synaptic contact and a typical synaptic cleft, 15 to 20 nm in width. From all these features, we can describe these neuro-odontoblast relationships as synaptic, based on immunological and morphological characteristics. Conclusion: Although it has previously been proposed that odontoblasts also could act as a specialised receptor cell, to date no synaptic or gap junctions connecting them with the nerve fibres have been described. In this investigation of mouse, rat and human odontoblasts and intrapulpal and intradentinal nerves, we demonstrated the presence of chemical synapses using electron microscopy and immunohistochemistry. Keywords: immunohistochemistry, neural endings, synapse, odontoblast, transmission electron microscopy