A histological study of the innervation of developing mouse teeth.

The innervation of developing mouse teeth between initial formation and crown formation was investigated using silver-stained serial sections. The developing innervation correlated with the stage of development of individual teeth rather than the chronological age of the mice. Nerves approached the developing dental papilla during the bud stage and formed a basal plexus below the dental papilla in the early cap stage. Nerve fibres from this plexus spread into the dental follicle as it began to develop. However, nerves did not enter the dental papilla until crown formation commenced, when the innervation was fairly rapid. Innervation commenced in the incisor teeth as soon as dentinogenesis started but not until a thin layer of enamel had been formed in the molar teeth. Although some of the early fibres were associated with blood vessels, many nerves lay free in the pulp. The absence of nerves in intimate relationship to the presumptive dental regions during the inductive phase of tooth development suggests that neural induction plays no part in the initiation of odontogenesis. However, it is not possible, from a purely histological study such as this, to attribute any function to the nerves at other stages of tooth development until the neurotransmitter content, and hence the type and likely function of the nerves, is established.