The ontogeny of substance P--containing nerve fibres in the developing mouse dentition.

The putative neurotransmitter, substance P, was localised in the developing teeth and periodontium of mice by indirect immunofluorescence. Substance P-containing fibres were visible in the incisor dental follicle eighteen days post-conception and entered the pulp two days after birth. The first molar pulp was innervated four days after birth and the second molar six days after birth. Innervation of the teeth by substance P fibres was delayed compared with the mucous and cutaneous innervation of adjacent areas and correlated with the stage of development of the teeth rather than the chronological age of the animal. The innervation of developing dental structures by substance P probably represents the establishment of a sensory supply prior to function of the tooth.