Development and terminal differentiation of pulp and periodontal nerve elements in subcutaneous transplants of molar tooth germs and incisors of the rat

Abstract

Ectopic tooth transplants are known to receive rich innervation of local neurons, but the precise location and structural features of neurites in the pulp and periodontal ligament (PDL) of such transplants are unclear. In this experiment, the molar tooth germs of rat embryos and incisors of young rats were subcutaneously transplanted into the dorsal regions of rats and processed, at various time intervals, for immunohistochemical demonstration of neural elements. Teeth with periodontal tissue elements developed in most of the molar transplants in 6 or 8 wk and received rich innervation, including some autonomic fibres, in the pulp. Nerve elements were also confirmed to be present in the PDL of these transplants, including specialized nerve ending-like structures reminiscent of the periodontal Ruffini endings. Mechanoreceptor-like structures were also induced in the regenerated PDL of similarly transplanted incisors, although the success rate was low. We conclude that rich and highly ordered innervation of the pulp, and occasional development of mechanoreceptors in the regenerated PDL of ectopic dental transplants, imply a high probability of successful induction of teeth with both nociceptive and mechanical sensations in the ectopic tooth and/or tooth germ transplant systems, although differentiation of mechanoreceptor-like nerve endings occured in only a few rare cases. © 2008 The Authors.