Question

In dislocation of the jaw, displacement of the articular disc beyond the temporomandibular (TM) joint results from spasm or excessive contraction of which of the following muscles?

• A. Buccinator
• B. Lateral pterygoid
• C. Masseter
• D. Temporalis

Hint:

Find the muscle that attaches to the articular disc itself and pulls the mandible forward.

Answer 1

The Correct Option is B

Step 1: Recall the muscle that moves the disc and condyle forward.
The lateral pterygoid is the main muscle that protrudes the mandible. Its upper head attaches directly onto the articular disc and the capsule of the temporomandibular joint, and its lower head attaches onto the neck of the mandibular condyle.

Step 2: Explain the mechanism of dislocation.
When the lateral pterygoid contracts too strongly or goes into spasm, for example during a wide yawn or forced mouth opening, it pulls both the condyle and the disc forward, past the summit of the articular eminence. Once the condyle slips in front of the eminence, the jaw locks open, this is TMJ dislocation, and the disc is displaced along with it.

Step 3: Rule out the other muscles.
Buccinator is a muscle of the cheek involved in chewing and blowing, not in moving the condyle or disc. Masseter and temporalis are both powerful muscles of mastication that close the jaw (elevate the mandible) and do not pull the disc or condyle forward past the eminence, if anything, they resist the movement that causes dislocation.

Step 4: Final conclusion.
The muscle responsible for anterior displacement of the disc and condyle beyond the joint, causing dislocation, is the lateral pterygoid, since it is the muscle that inserts on both the disc and the condylar neck and drives the mandible forward.
\[ \boxed{\text{Lateral pterygoid}} \]