Correct Answer: B. Lateral pterygoid
The lateral pterygoid muscle is the only muscle with direct anatomical attachment to the articular disc of the temporomandibular joint (TMJ). This muscle has two heads: the superior head attaches to the joint capsule, articular disc, and condylar neck, while the inferior head attaches to the condylar neck and mandibular angle. During jaw opening (as in yawning), the lateral pterygoid contracts to protract the mandible and simultaneously pull the disc anteriorly with the condyle, maintaining proper disc-condyle relationship. When the jaw locks during yawning, it typically results from anterior disc displacement without reduction—a condition where the disc moves forward but fails to return to its normal position during closure. The lateral pterygoid's dysfunction or spasm can contribute to this locking mechanism. Understanding this attachment is critical because it explains why lateral pterygoid pathology (myofascial pain, spasm, or trigger points) directly affects TMJ mechanics and disc position, a common presentation in Indian dental and ENT practice. The muscle's unique relationship with the disc makes it the only correct answer among the masticatory muscles.
Why the other options are wrong
A. Medial pterygoid — The medial pterygoid attaches to the medial surface of the mandibular angle and ramus, not to the articular disc. While it is a powerful jaw closer and contributes to TMJ stability through the joint capsule, it has no direct disc attachment. This is a common trap because students confuse all pterygoid muscles as having similar TMJ relationships. C. Temporalis — The temporalis muscle inserts on the coronoid process and anterior border of the mandibular ramus. It is a primary jaw closer and retracts the mandible but has no attachment to the articular disc. NBE may include this to test whether students conflate all muscles involved in jaw movement with disc attachment. D. Masseter — The masseter attaches from the zygomatic arch to the lateral surface of the mandibular angle and ramus, functioning as a powerful jaw closer. It has no relationship with the articular disc. This option exploits the fact that masseter is the strongest masticatory muscle, leading students to assume it must have the most complex TMJ attachments.
High-Yield Facts
- Lateral pterygoid superior head attaches directly to the articular disc and joint capsule; inferior head does not.
- Anterior disc displacement without reduction (ADDR) is the most common cause of TMJ locking and is related to lateral pterygoid dysfunction.
- Lateral pterygoid is the only masticatory muscle with direct articular disc attachment; medial pterygoid, temporalis, and masseter attach only to mandibular bone.
- Lateral pterygoid contraction during jaw opening protracts the mandible and pulls the disc anteriorly to maintain proper disc-condyle relationship.
- TMJ locking during yawning occurs when the disc displaces anteriorly and the lateral pterygoid fails to reposition it during closure.
Mnemonics
DISC DISC Direct attachment = Lateral pterygoid; Insertion on Superior head; Contraction pulls Disc; Inferior head skips disc; Stability role; Condyle coordination. Use when identifying which muscle controls disc position. Only Lateral Pterygoid Loves the Disc (OLP-LD) Among masticatory muscles, only Lateral Pterygoid has direct attachment to the articular disc. Medial pterygoid, Temporalis, and Masseter attach only to mandibular bone. Quick recall: if the question asks about disc attachment, the answer is always lateral pterygoid.
NBE Trap
NBE pairs jaw locking during yawning with masticatory muscle anatomy to test whether students confuse all jaw muscles as having equal TMJ involvement. The trap is assuming that the strongest jaw muscles (masseter, temporalis) must control the disc, when in fact only the lateral pterygoid has this specialized role.
Clinical Pearl
In Indian dental clinics, TMJ locking during yawning is a classic presentation of anterior disc displacement without reduction (ADDR). Patients report sudden inability to close the mouth fully after wide opening. Lateral pterygoid myofascial pain or spasm is a treatable cause; physiotherapy targeting this muscle often resolves the locking, making understanding its disc attachment clinically essential for diagnosis and management.
_Reference: Robbins & Cotran Pathologic Basis of Disease, Ch. 29 (Head and Neck Pathology); Gray's Anatomy (Indian edition), Ch. 8 (Muscles of Mastication); Bailey & Love's Short Practice of Surgery, Ch. 37 (TMJ Disorders)_