The mandibular division of the trigeminal nerve is the largest and most complex, being the only division with both sensory and motor fibres. Its motor root innervates all four muscles of mastication plus the floor of mouth muscles, while its sensory branches supply the lower face, lower teeth, tongue, and external ear. The inferior alveolar nerve carries sensation from all lower teeth and is the target of inferior alveolar nerve blocks for lower jaw dental anaesthesia.
| Origin | Trigeminal ganglion with additional motor root from the motor nucleus of V |
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Inferior alveolar nerve injury during mandibular third molar extraction produces lower lip numbness (mental nerve distribution) that is temporary in most cases from neurapraxia but permanent in approximately 1 percent when the nerve is transected. The lingual nerve lying medial to the wisdom tooth is also at risk, producing anterior two-thirds tongue numbness. Both injuries are more common with deeply impacted lower third molars.
V3 sensory branch damage during wisdom tooth extraction producing lower lip and chin numbness from mental nerve involvement, temporary in 90 percent but permanent in approximately 1 percent of cases.
The most common trigeminal neuralgia distribution, producing lancinating lower facial pain from mandibular nerve root compression at the brainstem.
