Innervation of the mandibular incisors by the mental nerve.

PURPOSE This study tested the hypothesis that some sensory innervation to the lower incisor teeth comes from reentry of the terminal branches of the mental nerve through the labial plate of the anterior mandible. PATIENTS AND METHODS Ten cadaveric heads (20 sides) were dissected and studied to determine whether the mental nerve crossed the midline or reentered the labial plate. Using careful dissection, the most posterior branch of the nerve was exposed from its point of emergence at the mental foramen to its insertions, and any entries into the labial plate were recorded and photographed. RESULTS Three of 20 (15%) specimens showed unequivocal evidence of nerve reentry into the labial plate. Five specimens displayed strong evidence of nerve fibers reentering the plate, but these were too fragile to be dissected through the periosteum without breaking. In 12 of 20 (60%) specimens, there were no branches identified that reentered the bone plate. Of the eight specimens showing evidence of reentry, four had substantial midline crossover. CONCLUSIONS The finding that branches of the mental nerve may reenter the labial plate to supply the lower incisors explains the phenomenon of crossover innervation from the contralateral mental nerve and the fact that a labial infiltration injection will anesthetize the lower incisor teeth.