EVIDENCE FOR A NEURAL INFLUENCE ON TOOTH GERM GENERATION IN A POLYPHYODONT SPECIES

It has been suggested that nerve endings emanating from the dental ner ve plexus of the jaw might be involved in the formation of tooth germs . In the present study we examine the effect of unilateral denervation on the formation of tooth germs in the lower jaw of a polyphyodont te leost-the cichlid Tilapia mariae. Repeated inspection of the lower jaw dentition in normal animals over a period of about 300 days showed th at the functional time of an average individual tooth is 101 days. In operated animals, the functional time was normal on the unoperated sid e, but on the denervated side tooth turnover ceased about 100 days aft er surgery. Radiographic plates from lower jaw specimens revealed that mineralized replacement teeth were present on the unoperated side, bu t not on the denervated side, 300 days after denervation. Light micros copic examination of semithin transverse sections from decalcified pla stic-embedded lower jaws showed that soft-tissue tooth primordia and n erves were lacking on the denervated side, while present within the un disturbed half-jaw. It is concluded that the local presence of mandibu lar nerve branches is necessary for the formation of tooth germs in th e lower jaw of the cichlid T. mariae. (C) 1994 Academic Press, Inc.