Immunocytochemical investigation of caries-induced neural, vascular and leucocyte responses in human primary and permanent tooth pulp.

This immunocytochemical study investigated nerve density and morphology, neuropeptide expression, vascular status and leucocyte accumulation within the human tooth pulp. It specifically examined differences between the primary and permanent dentition, and explored the effect of caries on the above parameters. The study also sought to correlate quantitative findings with a reported pain history.
Mandibular first permanent molars and second primary molars were obtained from children requiring dental extractions under general anaesthesia. A simple pain history was elicited for each patient. Following exodontia, teeth were split longitudinally, placed in fixative and were categorised as intact, moderately carious or grossly carious. The coronal pulps were removed and serial frozen sections were processed for indirect immunofluorescence. Triple-labelling regimes were employed using combinations of the following antisera: i) protein gene product 9.5 (a general neuronal marker; ii) the neuropeptides calcitonin gene-related peptide, substance P, vasoactive intestinal polypeptide or neuropeptide Y; iii) Ulex europeaus I lectin (a label for vascular endothelium) and iv) leucocyte common antigen (a general leucocyte marker). Image analysis was then used to determine the percentage area of immunostaining for each label within different anatomical regions of the coronal pulp.
The findings revealed that there were significant inter-dentition differences for the biological variables under investigation. Essentially, in intact samples, innervation density and neuropeptide expression were greater in permanent teeth but primary tooth pulps were more vascular and contained a greater number of leucocytes. With caries progression, both dentitions demonstrated significant increases in neural density, neuropeptide expression and leucocyte accumulation. However, changes in pulpal vascularity were limited to the pulp hom regions. The only factors found to correlate with the reported pain history were substance P and vasoactive intestinal polypeptide expression. These peptides were significantly upregulated in painful pulpitis. Finally, there was evidence to suggest that changes in neuropeptide expression were associated with changes in vascular status and leucocyte accumulation within the inflamed pulp.
In conclusion, this study has established that significant inter-dentition differences exist in pulpal biology. Furthermore, dynamic changes in pulpal neural density and neuropeptide expression seem to occur with caries progression. These findings are likely to have functional importance in terms of pain experience, inflammation and healing, and thus may help to direct the development of novel therapeutic strategies for the compromised dental pulp.