OCB02-1008 Molecular aspects of temporomandibular joint development

Question 1

Where does the TMJ form?

Answer 1

Between the glenoid/ mandibular fossa of the temporal bone and the condylar process of the mandible

Question 2

What does the temporal bone consist of?

Answer 2

Petromastoid, squamosal, tympanic and styloid

Question 3

What are the 3 processes of the proximal part of the mandible?

Answer 3

coronoid process
condylar process
angular process

Question 4

Where does the articulation of the TMJ to the temporal bone occur?

Answer 4

Condyle

Question 5

What do the angle and coronoid act as?

Answer 5

muscle attachment sites

Question 6

Where are the jaw closing muscles located?

Answer 6

In the coronoid

Question 7

Where are the jaw opening muscles located?

Answer 7

angular

Question 8

What are the purpose of ligaments in the TMJ?

Answer 8

To keep a fixed position

Question 9

What is ankylosis?

Answer 9

The disc and glenoid fossa fuse together preventing the complete opening of the jaw

Question 10

What is Auriculo-condylar syndrome?

Answer 10

Where all patients have a TMJ defect and 75% of patients are having problem with condylar size

Question 11

What are the 3 proximal elements of the jaw first formed via?

Answer 11

Intramembraneous ossification

Question 12

What are the 3 proximal elements of the jaw?

Answer 12

Bone is capped with secondary cartilage
Disc is formed between the joint
Cartilage is turned to bone via endochondral ossification

Question 13

Do humans have an angular process?

Answer 13

Initially, the jaw begins to produce an angular process, however humans do not need this, so the jaw adapts to form an angle instead

Question 14

What does the loss of angular TGF-B2 cause in mutant mice?

Answer 14

Leads to loss of muscle attachment due to a defect in the tendon
Loss of the angular is due to loss of mechanical stimulation

Question 15

What does the loss of the coronoid in the Pax9 mutant cause?

Answer 15

With the Pax9 gene in bone cells, they cannot synthesis a coronoid process
Temporalis muscle attachment is not lost with a loss of Pax9

Question 16

Where does secondary cartilage form?

Answer 16

Condyle

Anterior coronoid border but disappears before birth

Question 17

What replaces the majority of secondary cartilage in TMJ? Which site is an exception?

Answer 17

Bone replaces cartilage

Except for articulation site which remains cartilaginous

Question 18

How does the disc develop?

Answer 18

Disc forms on top of the condylar cartilage
Condensed tissue sits on top of the condyle
The disc lifts off the condyle and a lower cavity forms

Question 19

At what week is most of the TMJ established?

Answer 19

14

Question 20

What causes the separation of the disc to the condyle?

Answer 20

Formation of lubricin

Question 21

What is indian hedgehog?

Answer 21

Cell signalling protein

Question 22

What does a loss in indian hedgehog cause?

Answer 22

reduction in the condylar cartilage and failure in disc formation

Question 23

What occurs in the condyle when it is converted to bone?

Answer 23

Chondrocytes pass through the proliferative and hypertrophic zones before being replaced by osteoblasts and bone matrix

Question 24

What are the structures of chondrocytes in the outer region and inner region?

Answer 24

In the outer regions, the chondrocytes are flattened as they move down towards the hypertrophic zones, they become more rounded

Question 25

What do cells turn on when they turn to the bone phenotype?

Answer 25

Type X collagen

Question 26

What is needed to convert cartilage to bone?

Answer 26

Runx2

Question 27

Where in the mammalian body are the homologous bones that form the jaw articulation in non-mammals? And what are the names of the bones?

Answer 27

Middle ear

Incus and malleus

Question 28

How can you tell an animal has a big bite force from the mandible bone?

Answer 28

Big coronoid, big attachment, big bite