Inferior alveolar nerve !

The inferior alveolar nerve runs inside the lower jaw and gives feeling to the lower teeth, lip and chin; dentists numb it for lower dental work.

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What it is

A V3 branch running through the jawbone, coming out at the chin as the mental nerve.

What it does

Feeling of the lower teeth, lip and chin; numbed for dental work.

Key facts

Roots: V3; enters the mandibular foramen, exits the mental foramen as the mental nerve
Moves: Nerve to mylohyoid (leaves before the mandibular foramen): mylohyoid and anterior belly of the digastric
Feeling from: Lower teeth; lower lip and chin (mental nerve)

Relations

Course: Branch of the posterior trunk of the V3 mandibular nerve; descends deep to the lateral pterygoid, between the sphenomandibular ligament and the ramus, enters the mandibular foramen, runs forward in the mandibular canal below the molar and premolar roots and leaves through the mental foramen as the mental nerve, while an incisive branch continues to the canine and incisors
Medial: The sphenomandibular ligament and the medial pterygoid, with the lingual nerve in front
Lateral: The ramus of the mandible
Above: In the mandibular canal, the roots of the lower molars, especially the third molar, whose roots can touch or groove the canal

How to find it

The mental foramen, where the mental nerve emerges, usually lies below the second premolar (some texts: between the two premolars), about halfway between the gum line and the lower border of the mandible.

Examination

Light touch and two-point discrimination on the lower lip and chin, compared with the other side, map the numb area after dental surgery or a fracture

On imaging

A panoramic radiograph or cone-beam CT shows the mandibular canal as a dark band with white borders; darkening of a third molar root or a break in the canal's white line suggests the root lies close to the nerve.

Clinical notes

Fractures of the angle and body of the mandible can stretch or tear it in the canal, leaving the lip and chin numb
In jaws without teeth, bone loss brings the mental foramen close to the top of the ridge, where a denture can press on the mental nerve
Incomplete anaesthesia after a block can come from extra supply, such as the nerve to mylohyoid or fibres crossing the midline from the other side

Anatomical variants

A bifid (double) mandibular canal is seen on some radiographs and can explain a block that does not fully work

Test yourself

Think of the answer, then tap the question to see it.

What are the landmarks for an inferior alveolar nerve block?

The coronoid notch and the pterygomandibular raphe; the nerve lies in the pterygomandibular space just above the lingula and mandibular foramen.

Why does an inferior alveolar nerve block usually numb the side of the tongue too?

The lingual nerve lies just in front of it in the pterygomandibular space.

Where does the inferior alveolar nerve end, and what does injury after third molar surgery cause?

It leaves the mental foramen as the mental nerve; injury numbs the lower lip and chin on that side.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): nervus alveolaris inferior TA2 6274
Official Spanish (DeCS): Nervios alveolar inferior y mentoniano
English (TA2): Inferior alveolar nerve
Also called: nervus alveolaris mandibularis

Sources: Terminologia Anatomica (TA2); Anatomy, Head and Neck: Alveolar Nerve; Inferior Alveolar Nerve Block.

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Representative model, for educational purposes only.

Inferior alveolar nerve highlighted on the Durgical 3D model