Physiology & Biochemistry · patient case question
Which of the following is NOT a muscle of mastication?
Patient case: Punched-Out Papillae and a Tight Face
Patient: Two patients in the same session
Chief Complaint: (1) A 21-year-old student: “My gums are killing me and my breath is horrible.” (2) A 47-year-old woman referred with progressive facial tightness.
Background: Patient 1: final examinations week, sleeping four hours a night, smoking a pack a day, has not brushed properly in days. Patient 2: known systemic sclerosis, increasing difficulty opening her mouth.
Medications: Patient 1: none. Patient 2: nifedipine, omeprazole.
Vital Signs: Patient 1: T 100.6°F, HR 92, cervical lymphadenopathy. Patient 2: within normal limits.
Findings: Patient 1: punched-out, cratered, necrotic interdental papillae covered by a grey pseudomembrane, with spontaneous bleeding and severe pain. — Patient 2: taut shiny perioral skin with radial furrowing, maximum opening 26 mm, and on radiographs a uniformly WIDENED periodontal ligament space around multiple teeth which are firm and asymptomatic.
Show answer and explanation
Correct answer: A. Buccinator
1. Temporalis — elevation and retraction of mandible
2. Masseter — primary elevator/closer of mandible
3. Medial Pterygoid — elevation of mandible, assists in protrusion
4. Lateral Pterygoid — protrusion and opening of mandible
• Buccinator: a muscle of FACIAL EXPRESSION — innervated by the facial nerve (CN VII), buccal branch. It is the cheek muscle that keeps food between the teeth during chewing but is NOT a muscle of mastication.
• Buccinator originates from pterygomandibular raphe and alveolar processes; it compresses the cheek.
- A. The temporalis IS a muscle of mastication — it elevates and, through its posterior fibres, retrudes the mandible.
- B. CORRECT — this is the exception. The BUCCINATOR is a muscle of FACIAL EXPRESSION, innervated by the buccal branch of the FACIAL nerve (CN VII). It compresses the cheek against the teeth, keeping the food bolus on the occlusal table during chewing and preventing it from pooling in the vestibule. It assists mastication functionally but is not one of the four muscles of mastication.
- C. The masseter IS a muscle of mastication — the most powerful elevator, and the most superficial and easily palpated.
- D. The medial pterygoid IS a muscle of mastication — it elevates and protrudes and assists in lateral movement.
Note: The four muscles of mastication all derive from the FIRST branchial arch and are all innervated by the MANDIBULAR division of the trigeminal (V3): masseter, temporalis, medial pterygoid and lateral pterygoid. Nerve supply is the reliable way to separate them from the muscles of facial expression, which come from the SECOND arch and are supplied by CN VII.
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