Innervation of the continuously growing incisor.

Abstract

To my knowledge, the development of the innervation of the teeth has not yet been systematically investigated. There have been sporadic remarks ; for example, Holland1 writes : “As far as nerve tissue is concerned, it is believed that there is no direct connection or hookup with the parent sensory nerve ganglion until the tooth erupts and until root formation is nearly completed”. Different authors, for example, Powers2, in her studies of tooth innervation, has given illustrations of the rat-pulp for myelinated fibres but only from the molar teeth and illustrations of the periodontal nerve supply from the continuously growing incisor of the same species. In several animals (dog, calf, pig) I have found that in the earlier stages of the tooth development, for example, the period before the root begins to grow, there are in the pulp only unmyelinated (presumably vegetative) fibres. Later the myelinated sensory fibres appear. The pulp of the continuously growing incisor of the rat shows a similar situation. There are only unmyelinated fibres differing in size and branching. These are mainly in the neighbourhood of the vessels (see Fig. 1) and do not reach the odontoblastic layer.