Muscles of Mastication & TMJ — INBDE Review
The four muscles of mastication, TMJ joint mechanics (rotation vs translation), key ligaments for IAN block, and disc displacement patterns. 11 board-style MCQs.
Concept summary & clinical relevance.
Quick-reference structure first, then nerve-by-nerve detail. Mnemonics in amber, clinical pearls in blue.
All four muscles of mastication are innervated by the mandibular division of the trigeminal nerve (V3). Three close the jaw, one opens it. The TMJ itself is a modified synovial joint that uses two compartments to combine hinge and glide — a setup that explains both the mechanics of opening and the patterns of disc displacement.
| Muscle | Primary action | Insertion | Clinical note |
|---|---|---|---|
| Masseter | Elevates mandible (strongest bite force) | Mandibular angle (lateral) | Hypertrophies in bruxism — visible at angle |
| Temporalis | Elevates + retrudes (posterior fibers) | Coronoid process | Posterior fibers = retrusion |
| Medial pterygoid | Elevates + grinds | Mandibular angle (medial) | Mirror-image partner to masseter |
| Lateral pterygoid | Depresses (opens), protrudes, lateral shift | Condyle + articular disc | Only mastication muscle that opens the jaw |
| Compartment | Movement | When |
|---|---|---|
| Lower (condyle ↔ disc) | Rotation (hinge) | First 20–25 mm of opening |
| Upper (disc + condyle ↔ fossa) | Translation (glide over articular eminence) | Wide opening beyond 25 mm |
The four muscles of mastication
- Masseter: elevates mandible; strongest bite force; palpable at the angle when patient clenches.
- Temporalis: anterior/middle fibers elevate; posterior fibers retrude. Inserts on the coronoid process.
- Medial pterygoid: elevates and contributes to lateral grinding. Inserts on the medial mandibular angle (mirror to masseter).
- Lateral pterygoid: the only opener of the four. Also protrudes the mandible. Inserts on the condyle and articular disc — the anatomical reason it's central to disc disorders.
TMJ structure & motion
- TMJ = modified synovial joint with an articular disc dividing the joint into two compartments.
- Lower compartment: condyle rotates against the underside of the disc → first 20–25 mm of opening.
- Upper compartment: condyle + disc translate forward together over the articular eminence → wide opening.
- Bony landmarks: mandibular condyle (ball), mandibular fossa (socket), articular eminence (the slope).
Ligaments
- Lateral (temporomandibular) ligament: primary stabilizer; prevents posterior displacement of the condyle.
- Sphenomandibular ligament: landmark for the inferior alveolar nerve block.
- Stylomandibular ligament: minor support; limits excessive protrusion.
Movements & nerve supply
- Elevation (close): masseter, temporalis, medial pterygoid.
- Depression (open): lateral pterygoid + suprahyoid muscles (e.g., digastric).
- Protrusion: lateral pterygoid (main); medial pterygoid assists.
- Retrusion: posterior fibers of temporalis.
- Lateral shift (grinding): alternating pterygoids.
- TMJ capsule sensation: auriculotemporal nerve (branch of V3).
11 board-style MCQs.
Active recall is the highest-yield study method for the INBDE. Pick an answer, check it, and read why every distractor is wrong — that's where the learning compounds.
The MCQs above are Core Recall — testing what you've memorized. The book adds a full Clinical Integration set: board-style patient scenarios where you apply this anatomy to real clinical reasoning. That's the section the INBDE actually weights heaviest.
- Question 1EasyWhich cranial nerve innervates all four muscles of mastication?
- Question 2EasyWhich muscle is the primary elevator of the mandible and produces the strongest bite force?
- Question 3EasyWhich muscle is the only one of mastication that actively depresses (opens) the mandible?
- Question 4ModerateWhich muscle attaches to the articular disc of the TMJ?
- Question 5EasyThe TMJ is best classified as which type of joint?
- Question 6ModerateWhich bony structure must the condyle and disc slide over for wide mouth opening?
- Question 7ModerateWhich ligament is the primary stabilizer of the TMJ?
- Question 8ModerateWhich TMJ ligament is used as a landmark during inferior alveolar nerve block anesthesia?
- Question 9EasyWhich muscle is most responsible for protruding the mandible?
- Question 10ModerateWhich nerve supplies sensory innervation to the TMJ capsule?
- Question 11ModerateDuring initial mouth opening (the first 20–25 mm), which movement occurs at the TMJ?
900 INBDE-style MCQs with full explanations across 18 chapters — Core Recall plus board-style Clinical Integration scenarios — alongside Learning Summaries, Integration Bridges, and Review Boxes. Built by Dr. Isaac Sun for dental students who want to think like a clinician, not just memorize.
Founder, KYT Dental Services · Author, KYT INBDE series. These MCQs and Learning Summaries are part of a structural-thinking framework Dr. Sun uses with patients in the chair.