Course and composition of the nerves that supply the mandibular teeth of the rat

The rodent dentition has become an important model for investigations of interactions between dental tissues and peripheral neurons. Although experimental nerve injury has been widely used for such studies, there is uncertainty about the courses of nerve fibers supplying the mandibular teeth. In order to clarify this, we used a mixture of monoclonal antibodies against neurofilament proteins to enhance demonstration of nerve fibers so that small nerves could be readily traced in serial frozen sections of mandibles of Sprague Dawley rats ranging in age from embryonic day (E) 18 to postnatal day (P) 90. The 1st molar and anterior portion of the 2nd molar were innervated by small nerves that emerged as distinct branches of the IAN trunk at or near the mandibular foramen. In contrast, the nerve supply to the 3rd molar and posterior part of the 2nd molar was a branch of the lingual nerve that bypassed the mandibular canal altogether. The IAN trunk split into the mental nerve and a large branch to the incisor about 2 mm anterior to the mandibular foramen. Thick branches of the incisor nerve descended into the incisor socket to form a dense plexus of nerve fiber bundles extending along the length of the incisor periodontium. The sparse pulpal innervation of the incisor was provided by a few thin fascicles that emerged from the caudal portion of the periodontal plexus to enter the incisor apex. The dental branches of the IAN and lingual nerve seen in the adult were well established and readily identifiable at age E18 even though their targets were limited to the follicles of the developing teeth. These studies show that the trigeminal branches that supply the mandibular teeth can be identified at a wide range of ages as distinct nerves at a considerable distance proximal to their targets. This detailed information on the courses taken by the dental nerves can provide an anatomical basis for increased precision in characterization and perturbation of neural pathways from the molars and incisor.