A patient with a TMJ complaint has a jaw that deviates to the LEFT on opening, with assisted opening of only 32 mm. There is no pain. Which muscle is responsible?

Correct answer: D. Left lateral pterygoid

• A. Medial pterygoid raises the mandible — dysfunction causes closing problems, not lateral deviation on opening.
• B. Bilateral masseter spasm causes trismus (limited opening) without deviation.
• C. If the right lateral pterygoid were in spasm, the jaw would deviate to the RIGHT (toward the affected side).
• D. Correct. The jaw deviates toward the affected/restricted side during opening. Deviation to the LEFT indicates restriction in LEFT-side lateral pterygoid function (myospasm). The lateral pterygoid on one side pulls the condyle forward — if the left side cannot function properly, the jaw deviates left.