TMJ Flashcards
two bones
1) temporal and mandible
2) articular eminence
bony landmarks
1) mandibular fossa
2) articular eminence
3) squamotympanic fissure
- petrotympanic fissure
bony components of the TMJ
1) thin bone forms the roof of the fossa (area cannot withstand occlusal forces)
2) articular eminence is composed of dense bone that can withstand the forces of heavy loading
articular disc lies between the 2 bones
1) attached to joint capsule 360 around
articular disc of the TMJ
1) composed of dense fibrous connective tissue
2) better regenerative properties
3) can be better deformed
- flexible
4) wears better
5) not a great load bearing surface
capsular ligament
1) temporomandibular ligament
- outer oblique and inner horizontal portions
- both parts of the capsule
2) lateral portion is thicker than medial
3) limit disarticulation
joint spaces of the TMJ
1) 2 joint spaces
- separated by the articular disc
- form 2 separate synovial spaces with 2 different movements
2) upper joint space
- translation
3) lower joint space
- rotation
articular disc of the TMJ
1) attaches to condyle on medial and distal ligaments
2) biconcave
3) thinnest in center
4) thickest posteriorly
5) thicker medially than lateral
6) disc moves with the mandible
articular disc and distal ligaments
1) moves anteriorly and posteriorly with mandible and rotates over head of mandible
attachments of articular disc
1) anteriorly
- superior head of lateral pterygoid m. (inferior head to neck of condyle)
2) posteriorly
- retrodiscal tissue sandwiched between two lamina = bilaminar zone
- superior lamina = elastic fibers
- inferior lamina = collagen fibers
nerve supply of TMJ
1) primary
- auriculotemporal nerve to restrodiscal tissue
2) secondary
- masseteric nerve anteriorly
3) general sensory
- primarily to retrodiscal tissue
vasculature of TMJ
1) primarily to retrodiscal tissue
2) drainage to pterygoid venous plexus
biomechanics of the TMJ
1) closed
- condyle rests in the thinnest part, the inter mediate zone, against the posterior slope of the articular eminence
muscles of mastication
1) primarily elevators
muscle actions
1) jaw movements
- elevate
- depress
- retrude
- protrude
- lateral excursion
accessory muscles of mastication
1) suprahyoid and infrahyoid muscles
- minor assistance in jaw movement
biomechanics of TMJ
1) opening first movement is rotation
- within the inferior joint space (hinging)
- can only achieve limited opening
2) second movement is translation
- within the superior joint space
- can now achieve maximum opening
lateral movement
1) lateral pterygoid
2) medial pterygoid
3) anterior temporalis
4) medial temporalis
normal cycling of opening and closing
1) opening
- disc translates forward with the mandible while rotating posteriorly over its head
2) superior retrodiscal lamina stretches - it’s elastic
—
3) opening
- inferior head of lateral pterygoid is contracting
4 )closing
- superior head is contracting
—
when teeth bite into food, the condyle is fulcrumed away from the articular eminence
5) closing
- superior head of lateral pterygoid muscle balances posterior pull of elastic superior retrodiscal lamina to keep the disc positioned between the two bones
abnormal cycle
1) pops and clicks
2) in the closed position, the disc may not slide all the way back to its normal position
3) the head of the condyle rests on the posterior border of the disc rather than the intermediate zone
= anterior displacement (with or without reduction)
4) condyle pops over the posterior border of the disc (this is with reduction)
- creates pop or click
why doesnt the disc slide all the way back to its normal position?
1) the superior head of the lateral pterygoid muscle never fully relaxes
2) the superior retrodiscal lamina loses elasticity
3) the joint ligaments become lax
what may happen with abnormal cycle?
1) compression of retrodiscal tissues may cause degeneration, often with pain
2) then leading to degeneration of the articular surfaces
