The Temporomandibular Joint Flashcards
What is the temporomandibular joint?
It is the joint formed by articulation if the mandible with the cranium
Also known as the mandibular joint or jaw-joint
It is found anterior and roughly level to the tragus of the ear
It is the most complex joint in the body
What are the articular surfaces of the temporomandibular joint?
Superior
- On the under surface if the squamous part of the
temporal bone, there are 2 articular sites with sinuous
cross-sectional presentation
- Mandibular fossa (posterior and concave)
- Articular fossa (anterior and convex)
Inferior
- The condyle of the mandible had a rounded superior
edge & ellipsoid circumference with it’s major axis
postero-medial
What type of joint is the temporormandibular joint?
Synovial
What are the features of the TMJ capsule?
It has a fibrous capsule
The capsule is very strong in itself
The capsule is also very thin and loose to permit movements of the joint
Capsular attachments
Superiorly
- The circumference of the mandibular fossa and
articular tubercle
Inferiorly
- The neck of the condyle of the mandible
It is strengthened by extracapsular ligaments, one lateral and two medial
It remains liable to subluxation or complete displacement owing to its looseness
Does direct bone-to-bone articulation occur in the TMJ?
No.
A fibrous disc known as the articular disc or meniscus separates bony surfaces from making direct contact
This creates 2 cavities within the TMJ capsule - an upper and lower capsule
What do the two cavities of the TMJ allow?
Two separate types of movement (or displacement) of the joint
- A gliding joint (translational movement in the upper
cavity) - A modified hinge joint (rotational movements in the
lower cavity)
What are the articular surfaces of the upper cavity of the TMJ?
Articulating surfaces are:
- Articular surface of the under surface if the temporal
bone
- Upper surface of the articular disc
What are the articular surfaces of the lower cavity of the TMJ
Articulating surfaces are:
- The mandibular condyle
- Inferior surface of the articular disc
Describe the congruity between the articulatory surfaces of the TMJ
The superior and inferior articular surfaces are incongruous
Superior surface
- Convexo-concave (antero-posteriorly)
Inferior surface
- Condyloid with an oblique trajectory superiorly
The articular disc between bony articular surfaces makes them congruent
What are the articulatory surfaces of the TMJ lined with?
Fibrocartilage
Describe the articular disc in the TMJ
It is composed of dense fibrous connective tissue
It has the same composition as the fibrocartilage lining the articulatory surfaces
Upper surface is concavo-convex (antero-posteriorly) to fit both the mandibular fossa and articular tubercle
Inferior surface is concave for reception of the mandibular condyle
It is thicker at its periphery where it attaches to the articular capsule
It can recoil or stretch a little with movement
It is thinner centrally
And it makes the articulating surfaces congruent
How does the inferior bony articulatory surface of the TMJ Move and work?
It is condyloid
Its surface area is significantly lower than its superior counterpart
It can move anteriorly to articulate with anterior superior articular surface
This movement is known as translation or protrusion
Translational movements of the condyle are in an oblique plane
When the jaw is closed, it articulates with the posterior superior articular surface
Rotational movements occur when the condyle is engaged in the concavity of the posterior superior articular surface.
What are the extracapsular ligaments of the TMJ?
One lateral ligament:
Temporomandibular ligament:
- The strongest ligament of the TMJ
- Its deep fibres blend with the capsule
- Attachment: - Lower border of zygoma to posterior
border of neck & ramus of mandible
- It tightens the head in retrusion (closing & pulling jaw
backwards)
And two medial ligaments that strengthen the capsule, but they are less significant
What are the accessory ligaments of the TMJ?
Sphenomandibular ligament:
- It remains constant in length and tension for all
positions of the mandible
- It prevents inferior dislocation of the joint
- It goes from the spine of the sphenoid bone to the
mandibular foramen
Stylomandibular ligament:
- It extends from near the apex of the styloid process
to the posterior border of the ramus of the mandible
near its angle
- It is a thickening of the deep parotid fascia
- It separates the parotid gland from the submandibular
gland
When is the TMJ the most stable?
When the jaw is closed
The mandibular condyle is in contact with mandibular fossa
Teeth are in occlussal contact
Perfect occlusion further stabilises the joint
Least stable when the jaw is open
