OCB02-1008 Molecular aspects of temporomandibular joint development Flashcards
Where does the TMJ form?
Between the glenoid/ mandibular fossa of the temporal bone and the condylar process of the mandible
What does the temporal bone consist of?
Petromastoid, squamosal, tympanic and styloid
What are the 3 processes of the proximal part of the mandible?
coronoid process
condylar process
angular process
Where does the articulation of the TMJ to the temporal bone occur?
Condyle
What do the angle and coronoid act as?
muscle attachment sites
Where are the jaw closing muscles located?
In the coronoid
Where are the jaw opening muscles located?
angular
What are the purpose of ligaments in the TMJ?
To keep a fixed position
What is ankylosis?
The disc and glenoid fossa fuse together preventing the complete opening of the jaw
What is Auriculo-condylar syndrome?
Where all patients have a TMJ defect and 75% of patients are having problem with condylar size
What are the 3 proximal elements of the jaw first formed via?
Intramembraneous ossification
What are the 3 proximal elements of the jaw?
Bone is capped with secondary cartilage
Disc is formed between the joint
Cartilage is turned to bone via endochondral ossification
Do humans have an angular process?
Initially, the jaw begins to produce an angular process, however humans do not need this, so the jaw adapts to form an angle instead
What does the loss of angular TGF-B2 cause in mutant mice?
Leads to loss of muscle attachment due to a defect in the tendon
Loss of the angular is due to loss of mechanical stimulation
What does the loss of the coronoid in the Pax9 mutant cause?
With the Pax9 gene in bone cells, they cannot synthesis a coronoid process
Temporalis muscle attachment is not lost with a loss of Pax9
Where does secondary cartilage form?
Condyle
Anterior coronoid border but disappears before birth
What replaces the majority of secondary cartilage in TMJ? Which site is an exception?
Bone replaces cartilage
Except for articulation site which remains cartilaginous
How does the disc develop?
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
At what week is most of the TMJ established?
14
What causes the separation of the disc to the condyle?
Formation of lubricin
What is indian hedgehog?
Cell signalling protein
What does a loss in indian hedgehog cause?
reduction in the condylar cartilage and failure in disc formation
What occurs in the condyle when it is converted to bone?
Chondrocytes pass through the proliferative and hypertrophic zones before being replaced by osteoblasts and bone matrix
What are the structures of chondrocytes in the outer region and inner region?
In the outer regions, the chondrocytes are flattened as they move down towards the hypertrophic zones, they become more rounded
What do cells turn on when they turn to the bone phenotype?
Type X collagen
What is needed to convert cartilage to bone?
Runx2
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?
Middle ear
Incus and malleus
How can you tell an animal has a big bite force from the mandible bone?
Big coronoid, big attachment, big bite
