Which term describes involuntary contraction of jaw muscles that limits mouth opening?

• A. Trismus
• B. TMJ ankylosis
• C. Dyskinesia
• D. Myalgia

Answer: (A)

Trismus is the involuntary contraction or spasm of the jaw muscles that limits how wide you can open the mouth. It often follows dental procedures, facial trauma, infection around the jaw, or tetanus, and you’ll typically assess the opening distance to gauge severity (normal is roughly 40–50 mm). The key is that the limitation comes from muscle tone, not a fixed structural change.

TMJ ankylosis describes a true mechanical fusion of the temporomandibular joint, so opening is restricted because the joint itself is fused, not because the muscles are spasming. Dyskinesia means abnormal movements, which can involve various muscles but aren’t specifically about an acute, involuntary jaw-closing spasm limiting opening. Myalgia is muscle pain, which can accompany jaw problems but does not by itself explain restricted mouth opening.

Understanding trismus helps guide management, which focuses on addressing the underlying cause (infection, trauma, tetanus, aftercare) and often includes gradual jaw exercises, analgesia, and anti-spasmodics as appropriate.