Extra information... Flashcards
What is the TMJ?
Temporomandibular joint - articulation between temporal bone and mandible.
It is a synovial hinge-type joint divided into two synovial cavities by fibrocartilagenous disc.
What conditions can involve the TMJ?
TMJ disorder - pain (often refers to ear, jaw, lateral side of head) clicking locking.
TMJ dislocation -secondary to trauma, yawning
Arthritis
What is the TMJ innervated by?
Auriculotemporal nerve (branch of the mandibular division of the trigeminal nerve)
Describe the anatomy of the TMJ
The articular surfaces of bones lined with fibrocartilage are separated by fibrocartilagenous discs (to stop them coming into direct contact).
This divides the joint into two synovial-line cavities filled with synovial fluid.
This is stabilised by a joint capsule and a series of three extra capsular ligaments.
How does the jaw open initially (depression of the mandible)?
Hinge action - inferior half of joint cavity
How does the jaw open more widely?
Requires condyles of mandible to glide forward over the articular tubercle: this movement occurs in superior half of joint cavity.
How does the jaw protract and retract?
Involves movements at the superior joint capsule - gliding
What muscles are involved in elevation of mandible at TMJ?
Masseter
Temporalis
Medial pterygoid
What muscles are involved in depression of mandible at TMJ?
Lateral pterygoid
Gravity
Against resistance - platysma, supra hyoids (infra hyoids stabilise the hyoid bone)
What muscles are involved in protrusion of mandible at TMJ?
Lateral pterygoid
Medial pterygoid (assists)
(anterior fibres of temporals also assist)
What muscles are involved in retraction of mandible at TMJ?
Posterior fibres of temporalis (inserts into coronoid process)
What muscles are involved in grinding (lateral and rotational movement, alternate protrusion and retraction) of mandible at TMJ?
Muscles of two sides working co-operatively (lateral pterygoigs laterally deviate mandible)
What happens if TMJ is dislocated?
This occurs in facial trauma (if jaw is open) and yawning.
Jaw locks as joint fixes in open position due to anterior dislocation of condyle over the articular tubercle
Contraction of muscles around joint (muscles of mastication) keep joint locked in anterior displacement.
