Sodium channel Nav1.8 immunoreactivity in painful human dental pulp

Using specific antibodies for immunohistochemistry, we studied Nav1.8 – immunoreactivity in human dental pulp in relation to the neuronal marker neurofilament. Human tooth pulp was extracted from teeth harvested from a total of twenty-two patients (fourteen without dental pain, eight patients with dental pain).Fibres immunoreactive for Nav1.8, were significantly increased on image analysis in the painful group: median (range) Nav1.8 to Neurofilament % area ratio, non-painful 0.059 (0.006–0.24), painful 0.265 (0.13–0.5), P = 0.0019.Nav1.8 sodium channels may thus represent a therapeutic target in trigeminal nerve pain states.Pain is the most common symptom of diseased tooth pulp, often a result of coronal caries of the tooth, affecting up to 80% of the western population during their lives. The mature human dental pulp is densely innervated with over 900 axons entering the average human premolar tooth [1] that originate from the trigeminal ganglion. The normal pulp seems insensitive to exteroceptive stimuli; however, in pathological states, electrical, thermal, mechanical and chemical stimuli all produce a nociceptive response [2]. Primary and permanent tooth pulps contain 70–90% C-fibres [3], myelinated fibres mostly of the A delta category [3], with few myelinated fibres of the A beta group. The majority of nerve fibres terminate in the coronal region of the pulp, forming a subodontoblast plexus, with 40% terminating in the dentinal tubules close to the odontoblast processes [3]. Strong correlations have been reported between the afferent discharge frequency of human pulp nociceptors and pain levels [4]. Many suggestions have been made for the origin of pulpal pain e.g. pulp inflammation involving several mediators located within the pulp (cholinergic and adrenergic neurotransmitters, prostaglandins and cyclic AMP). However, thus far, no correlation has been established between pain characteristics and histology of the pulp [5,6].Voltage-gated sodium channels play