Anatomy Of TMJ

Question 1

Superior surface of the TMJ

Answer 1

Under surface of the squamous part of temporal bone:
Mandibular fossa and articular tubercle

Question 2

Inferior surface of the TMJ

Answer 2

Condyle of the mandible

Question 3

How and why is the TMJ a modified synovial joint?

Answer 3

Fibrocartilage covering articulatory surfaces instead of hyaline
Hyaline would not be suitable for the high forces generated by the TMJ, as it’s epithelium would be damaged. Fibrocartilage can withstand much more.

Question 4

A fibrocartilage articular disc cuts the intro-capsular compartment into 2. What does each compartment allow?

Answer 4

Superior articulatory compartment allows for translational gliding movements
Inferior articulatory compartments allows for rotational movements - modified hinge movement

Question 5

Describe the fibrous capsule of the TMJ

Answer 5

Very strong. Thin and loose to permit movements of the joint. Reinforced by extra-capsular ligaments.

Question 6

What is the TMJ lined with at birth?

Answer 6

Fibrocartilage in TMJ is lined by synovial membrane, but the amount of force generated breaks it down, so it does not remain in the adult.

Question 7

Describe the articular disc of the TMJ

Answer 7

Thicker at the periphery where it attaches to the articular capsule and thinner centrally. Dense fibrous CT. Largely incompressible. Can recoil or stretch a little with movement due to its attachments.

Question 8

Where does the capsule of the TMJ attach?

Answer 8

Superiorly to the circumference of the mandibular fossa and articular tubercle and inferiorly to the neck of the condyle.
Stabilised by extra-capsular ligaments.

Question 9

Some criteria of synovial joints

Answer 9

Synovial joint capsule with synovial fluid in it secreted by a synovial membrane
Reinforcement by extra-capsular ligaments

Question 10

Which is the strongest extra-capsular ligament?

Answer 10

The Temporomandibular/lateral ligament

Question 11

Where does the temporomandibular ligament attach?

Answer 11

Superiorly to the lower border of the zygomatic and inferiorly to the posterior border of the neck/ramus of mandible

Question 12

Function of TMJ ligament?

Answer 12

Tightens the head in retrusion

Question 13

What is the function of the sphenomandibular ligament?

Answer 13

Remains constant in length and tension for all positions of the mandible. Prevents inferior dislocation of the joint due to preventing the separation between articulatory surfaces.

Question 14

Where does the stylomandibular ligament join?

Answer 14

Attaches the posterior aspect of the angle of the mandible to the apex of the styloid process.

Question 15

Stability of the TMJ

Answer 15

Most stable when jaw is in closed position, even more when teeth are in perfect occlusion
Less stable when jaw is open. Liable to spontaneous dislocation in edentulous people.

Question 16

Movements occur by displacements in the:

Answer 16

Superior joint cavity (gliding) - protrusion and retraction
Inferior joint cavity (hinge) - depression and elevation

Question 17

What happens in jaw-opening?

Answer 17

Condyle are pull forward - protrusion gliding movement via the lateral pterygoid muscles acting in the upper join cavity.
Chin is pulled down and back, hinge movement by the digastric muscles acting in the lower joint cavity.

Question 18

How is the jaw-closed?

Answer 18

Retraction of the mandible - posterior fibres of the temporalis pull the mandible backwards, acting in the upper joint cavity.
Elevation of the mandible by the remainder of temporalis, masseters, medial pterygoids all acting in the lower joint cavity.

Question 19

What prevents inferior dislocation of the TMJ?

Answer 19

Sphenomandibular ligament (internal lateral) and stylomandibular ligament (posteriorly)

Question 20

What limits passive anterior displacement of the TMJ?

Answer 20

Articular tubercle

Question 21

What limits posterior displacement of the TMJ?

Answer 21

Post-glenoid tubercle.