The inferior alveolar nerve is the primary sensory supply to the lower teeth and the terminal mental nerve for chin and lower lip sensation. It is the most commonly blocked nerve in dentistry, the inferior alveolar nerve block anaesthetises all lower teeth on that side plus the chin and lip. The nerve is at risk in mandibular fracture, sagittal split osteotomy, and mandibular implant placement.
| Origin | Mandibular nerve (V3, third division of the trigeminal) |
|---|---|
| Course | Enters the mandibular foramen on the medial ramus, runs forward in the mandibular canal below the tooth roots giving dental branches, and divides near the premolar apices into the mental nerve, which leaves through the mental foramen to the chin and lower lip, and the incisive branch to the anterior teeth |
| Motor | |
| Sensory |
|
Persistent lower lip and chin numbness after mandibular surgery, such as sagittal split osteotomy, genioplasty, third molar extraction or implant placement, indicates inferior alveolar nerve injury; many cases recover within six months. Cone beam CT shows the canal in relation to tooth roots and planned implants and can reveal variants such as a bifid canal. An implant that encroaches on the canal should be removed or backed out promptly, as early decompression improves recovery. Microsurgical repair of a complete transection restores useful sensation in many patients.
Lower lip and chin numbness after mandibular surgery or fracture is managed by observation for several months, with microsurgical repair for complete lacerations.
A dental implant placed into or against the mandibular canal causes lip and chin numbness or pain; prompt removal or repositioning of the implant gives the best chance of recovery.
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