Methods: A total of 43 lower mandibular first permanent molars were obtained from children undergoing routine extractions, and the teeth categorised as intact (n=25) or grossly carious (n=18). Grossly carious teeth were sub-grouped as painful or non-painful on the basis of symptoms occurring within 48 hours prior to the extraction. Coronal pulps were removed and processed for indirect immunofluorescence using antibodies raised against TRPM8 and either the neuronal marker, protein gene product 9.5, or alpha smooth muscle actin in conjunction with ulex europaeus agglutinin 1 lectin to fully label the pulp vasculature. The level of expression of TRPM8 was quantified using image analysis.
Results: TRPM8 was expressed in both neuronal and vascular tissue in all teeth examined. There were no significant differences between the level of neuronal or vascular TRPM8 expression in carious and non-carious teeth (p>0.05 independent sample t-test). However, in the mid-coronal pulp region, expression of neuronal TRPM8 was significantly lower in carious painful samples than in carious non-painful samples (p=0.037). There appeared to be higher vascular TRPM8 expression within the pulp horn region of carious painful samples, but this difference was not significant.
Conclusions: The level of pulpal TRPM8 expression appears to be unaffected by the presence of caries. However, there are differences between the expression of neuronal TRPM8 in painful and asymptomatic teeth, suggesting that it may be involved in the initiation or response to pain.