Formation of the Mandible and Temporomandibular joint Flashcards
Ossification Centers
Initial appearance of bone tissue in the area where each of the 206 bone organs of the body form
Intramembranous ossification centers
Ossification centers in the mesenchyme
Endochondral ossification centers
Ossification centers within a cartilage model
T/F - the number of ossification centers vary from bone to bone
True
How many ossification centers are in the mandible?
2 - one for each half
How many ossification centers are in the maxilla?
2 for each bone (4 total)
Mixed ossification centers
Some bones have both intramembranos and endochondral ossification centers
What is an example of a bone that has a mixed ossification center?
Temporal bones
Intramembranous bone tissue formation
Highly vascular connective tissue where all bone formation occurs
Growth sites
Where bone tissue is added to a bone organ
Paired Meckel’s Cartilage
Temporary skeleton of mandibular processes of branchial arch I
Serve as a temporary attachment for muscles that eventually attach to mandible
Serves as temporary anterior lingual plate of forming mandible halves
Serves as an enclosed growth site at the chin end of the mandible halves
Meckels cartilage serves as a model for what?
2 ear ossicles - malleus and incus
What appears at the site of Meckel’s cartilage
2 ligaments - anterior mallelar and sphenomandibular ligaments
What happens to Meckel’s cartilage?
It undergrows growth, mineralization, and resorption while serving as an anterior growth site and is replaxed as temporary anterior lingual plates by encroaching bone tissue of the growing mandible halves
When does mandible formation start?
6th embryonic week
Where are the ossification centers for mandible formation
Within the mesenchymal tissue lateral to Meckel’s cartilage at the site of the future mental foramina (where the mental and incisive nerves branch from the inferior alveolar)
In what direction does the mandible grow from the ossification centers?
Anterior and Posterior
Anterior growth of the mandible
The bone incorporates the distal parts of Meckels’ cartilage
This iscorporated part of the cartilage becomes the temporary lingual plate and growth site of each mandible half
Posterior growth of the mandible
The bone is in the form of a ‘U’ (or trough) featuring facial and lingual plates
The posterior end of the facial plate incorporates an independent piece of hyaline cartilage that becomes ‘condylar cartilage’ - another growth site of each mandible half
When does osseous union between the 2 mandibular halves occur?
At the end of the first postnatal year
Condylar cartilage
An independent, cone-shaped area of cartilage that becomes enclosed in the posterior end of the facial bone
Fate of the proximal end of Meckel’s cartilage
Becomes the malleus and incus ossicles
Becomes the anterior mallelar ligament
Fate of the middle area of Meckel’s cartilage
Becomes the Sphenomandibular ligament
Fate of the distal end of Mecke’s cartilage
Temporary anterior lingual plate
Growth sites of the mandible halves - the cartilage mineralizes, resorbes, and is replaces by bone tissue of the anterior lingual plate of the mandible
Joint definition
A place of union or junction between two or more bones of the skeleton
What are the different types of joints
Synarthrosis Amphiarthrosis Diarthrosis Ginglymoarthrodial Gomphosis
Synarthrositic joint
Permits little or no mobility
Fibrous and suture jointss
Synarthrositic joint example
Between maxillary bones
Amphiarthrosis joint
Permits slight mobility
Cartilagenous joints
Amphiarthrotic joint example
Pubic Symphysis
Diarthrotic joint
Permits a variety of movements
Synovial joints
Diarthrotic joint example
Temporomandibular joint
Ginglymoarthrodial joint
Dual compartment
Gomphosis joint
A joing that binds a tooth to a bone socket
What are features of most freely moveable joints?
One joint cavity
Incomplete articular disc
Cartilage articular surfaces
What freely moving joint is different from the rest?
TMJ
What are some unique features of the TMJ?
Formed by the joining of the temporal and mandibular bones
Complete articular disc
Two joint concavities
Soft connective tissue articulating surface
Hyaline Cartilage of the condyle
Growth site for the mandible
Appositional growth occurs between the articular connective tissue surface and the condylar cartilage
At the lower end, the cartilage is mineralized, resorbed, and replaced by bone
When is the condylar cartilage replaced by compact bone?
Age 25
When does 2 ossification centers of the mandible form?
6th week IU
When does the blastema appear?
8th week IU
When does cavitation within the blastema of the TMJ appear?
3rd month IU
TMJ blastema
Where the condylar cartilage, articular disc, two joint concavities, and soft tissue articular surfaces all form
