Anatomy & Histology · single question
A patient with trismus (inability to fully open the mouth) has the MOST likely involvement of which muscle?
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Correct answer: B. Medial pterygoid
Trismus (inability to open the mouth = elevator muscle spasm) is most commonly from MEDIAL pterygoid spasm — often after IAN block injections.
- A. Temporalis is an elevator/retractor — while it can contribute to trismus, medial pterygoid is more commonly cited in dental post-injection trismus.
- B. CORRECT. Trismus most commonly results from medial pterygoid spasm. This elevator muscle is commonly affected by inadvertent injection during IAN block (which can enter the medial pterygoid), inferior alveolar abscess spread, or post-extraction infection.
- C. Lateral pterygoid OPENS the mouth — spasm would prevent closing, not opening.
- D. The digastric depresses the mandible (opens mouth) — spasm would open the mouth, not cause trismus.
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