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Oral Surgery · single question

A patient's mandible deviates to the LEFT during mouth opening. Which muscle is RESPONSIBLE (dysfunctional) for this deviation?

  1. Left masseter
  2. Right lateral pterygoid (the normal side pulls unopposed, deviating jaw to left because the left side is weak)
  3. Left lateral pterygoid (the weak side)
  4. Right temporalis
Show answer and explanation

Correct answer: C. Left lateral pterygoid (the weak side)

  • A. The masseter is an elevator — it does not cause the described deviation.
  • B. This describes the opposite mechanism — the right lateral pterygoid works normally. The question asks which muscle is responsible for the deviation.
  • C. Correct. The LEFT lateral pterygoid is the dysfunctional muscle. When it fails to adequately contract, only the right lateral pterygoid pulls the right condyle anteriorly, deviating the jaw to the LEFT (toward the weak side).
  • D. The temporalis (posterior fibers retract, vertical fibers elevate) — not responsible for opening deviation.

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