The re-expression of nerve growth factor protein after cavity preparation in rat molars

It is well known that nerve growth factor (NGF) is expressed in the odontoblasts of developing teeth, but not in completely grown teeth in rats. However, there have been no detailed studies of the expression of NGF in reactivated primary odontoblasts or in newly differentiated odontoblast-like cells during pulp repair. Therefore, to examine the involvement of NGF in odontoblasts during pulp repair, we immunohistochemically observed the localization of NGF in dental pulp after cavity preparation in rat molars. Based on the depth of the cavity, two types of pulp reaction were thus distinguished. 1) In shallow cavities, primary odontoblasts secreted a new dentin matrix, reactionary dentin, and also expressed NGF. 2) In deep cavities, odontoblast-like cells, differentiated from pulpal mesenchymal cells, formed a large amount of reparative dentin or osteodentin. Additionally, intense NGF-like immunoreactivity was observed in odontoblast-like cells. These results suggest that NGF not only acts as a neurotrophic factor of dental pulp, but is also involved in the differentiation and functional change of odontoblasts during pulp repair.