Dental pulp innervation

The mammalian dentition is of ultimate importance for survival in the animal kingdom. It is thus not surprising that teeth are equipped with a sophisticated, protective neurosensory system that mediates the sensation of pain. Impressive progress in the understanding of this system has made it evident that it differs in many ways from pain detecting networks at other body sites. Despite this, fundamental issues regarding the formation, structure, reaction to injuries, and especially the transduction mechanisms of the sensory system within the dental pulp remain elusive. From a functional standpoint, it appears enigmatic why most or all stimuli that excite pulpal nerve fibers, whether noxious cold or noxious heat to a fully intact tooth, or extremely light mechanical forces or subtle thermal, osmotic, or chemical changes to exposed dentin, result only in the sensation of pain, with no mechanism for discrimination. To maintain an efficient afferent transduction system in highly mineralized teeth, there is a need for a low-threshold sensory apparatus that will be able to detect stimuli through a hard shell of calcified tissue. Activation of highly sensitive intradental mechanoreceptors would alert to potentially endangering hardness and texture of food or other intraoral objects. This, in turn, would provide input for coordination and reflex activity of the masticatory muscle complex. Nerve fibers with higher thresholds would also be required to record and report on inflammatory threats. The pulp of the tooth seems to possess both these nerve fiber types. At odds with the current general concepts of pain transduction, the low-threshold mechanosensory fibers apparently connect to central pain-mediating, rather than tactile-mediating, pathways. In fact, intrapulpal nerves are probably the main source of tissue-damaging stimulus signaling from the dentition, while periodontal afferents serve to provide information on tooth load when subjects contact and gently manipulate food.