Head & Neck Anatomy · Dental

Muscles of Mastication

Four muscles — all V3 — perform mastication. Three elevate the mandible; one depresses and protrudes it.

✦ The Mnemonic

"Masticating Takes Methodical Lateral control"

Masseter · Temporalis · Medial Pterygoid (elevators) + Lateral Pterygoid (depressor/protrusion)

M Masseter Elevation + protrusion; superficial to TMJ; up to 800 N bite force

T Temporalis Elevation + retraction; fan-shaped; temporal fossa

M Medial Pterygoid Elevation + protrusion; forms 'mandibular sling' with masseter

L Lateral Pterygoid Depression + protrusion + side-to-side movement; only jaw opener of the four

📚 Clinical Breakdown

All four muscles are innervated by the motor root of V3. In a unilateral V3 motor lesion, the jaw deviates toward the side of the lesion on opening — unopposed contralateral pterygoids push it across.

Trismus (lockjaw) is spasm of the masseter and medial pterygoid. Causes include tetanus (risus sardonicus from masseter spasm), peritonsillar abscess, parotid abscess, and mandibular condyle fracture.

The lateral pterygoid has two heads. The upper head inserts into the articular disc — dysfunction causes disc displacement and the characteristic TMJ 'click' on jaw opening.

Jaw elevators Masseter, Temporalis, Medial pterygoid

Jaw depressor/protrusion Lateral pterygoid

Jaw deviation on opening Toward the V3 motor lesion

All supplied by V3 motor root

⭐ Clinical Pearl

Buccinator is NOT a muscle of mastication — it is supplied by CN VII (facial nerve). It compresses the cheeks against the teeth to prevent food accumulating in the vestibule. Its nerve supply (CN VII buccal branch) distinguishes it from the masticatory muscles.

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