TMJ Flashcards
what is a ossification center?
initial appearance of bone tissue in the area where each of the 206 bone organs of the body form
how many adult bone organs are there?
22 including 1 mandible, 2 maxilla
what is intramembranous bone organ development?
ossification center appearing within mesenchyme
ex. mandible, maxillary bones
what is endochondral bone organ development?
ossfication center appearing on or within a cartilage model
ex. ulna, femur
what is the difference of centers from bone to bone?
number of centers vary
how many ossification center does the mandible have?
2 (1 for each half)
how many ossification center does maxillary bones have
2 ossification center for each bone
what are mixed ossification centers?
have both intramembranous and endochondrial ossification centers- such as temporalbone
what are growth sites?
addition of bone tissue to bone organ
what are the growth sites of bone tissue formation?
periosteum, endosteum, haversian and volkmann canal, pdl
what is intramembranous bone tissue?
highly vascular connective tissue that bone tissue forms within
where are meckel’s cartilage?
one in each mandibular process of branchial arch 1
what is the role of meckel’s cartilage?
temporary skeleton of mandibular processes of branchial arch 1
serve as temporary attachment for muscles that eventually attach to mandible
each cartilage serves as models for 2 ear ossicles: malleus and incus
each serve as site for the appearance of 2 ligaments anterior mallelar and sphenomandibular
serve as temporary anterior lingual plate of forming mandible halves
serve as enclosed growth sites at the chin end of the mandible halves
what is the fate of meckel’s cartilage?
from the proximal part (inner ear cavity) to the distal part (chin), each cartilage serves as sites for:
- endochondral ossification centers for 2 ear ossicles: incus and malleus
- undergo retrogressive changes becoming 2 ligaments: anterior mallelar and sphenomandibular
- undergo growth, mineralization and resorption while serving as anterior growth sites and replaced as temporary anterior lingual plates by the encroaching bone tissue of the growing mandible halves
what does meckel’s cartilage serve as?
both ossfication centers of ear ossicles and as growth site of each mandible halves
what does enclosed anterior part of meckel’s cartilage serve as?
temporary lingual plate of the mandible halves
growth site of the developing mandible halves
how is the mandible formed?
mandible develops as 2 bilateral halves that exist through the interuterine period
when does osseous union occur between the halves of mandible?
end of first postnatal year
when does the mandible begin development?
6th embryonic week
what does the mandible arise from?
2 bilateral ossification centers within mesenchymal tissue, lateral to meckel’s cartilage
where does the ossification center appear?
in the area where the inferior alveolar nerve branches into the mental and incisive nerves or the site of future mental foramina
in what direction does the bone grow from the ossification centers?
anterior and posterior
what is the anterior growth?
the bone incorporates the distal parts of meckel’s cartilages: this incorporated part of each cartilage become temporary lingual plate and a growth site of each mandibular half-toward the midline of the chin where the 2 halves approach each other
what is the posterior growth?
the bone is in the form of a “U” 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 -grows posterior to the site of the future tmj
does condylar cartilage arise from meckel’s cartilage?
no, independent
what happens at the end of first postnatal year?
an osseous union occurs between 2 mandibular halves at distal or chin site: mandible becomes 1 of 22 skull bones
what happens to proximal end of each cartilage
serves as the model for 2 ear ossicles and 1 ligament
malleus and incus ossicles (bones)
anterior mallelar ligament
what happens to the middle area of each cartilage
sphenomandibular ligament
what happens to distal end of each cartilage
temporary anterior lingual plate and growth site of mandibular halves
- start meckel cartilage enclosure
- meckel cartilage enclosed
- meckel cartilage mineralized, resorbed, and replaced by bone tissue- anterior lingual plate of mandible
definition of joints or articulations
the place of union or junction between two or more bones of the skeleton
synarthrosis
permits little or no mobility (fibrous and suture joints)
ex. between maxillary bones: between temporal and parietal bones
amphiarthrosis
permits slightly mobility (Cartilaginous joints)
ex. pubic symphysis
diarthrosis
permits a variety of movements (synovial joints)
ex. tmj
ginglymoarthrodial joint
dual compartment structure and function:
ginglymo and arthrodial
ex. gomphosis joint- joint that binds a tooth to bone socket
features of most freely movable joints
one joint cavity
incomplete articular disc
cartilage articular surfaces
are features of most freely movable joint true for TMJ?
no
What two bones form the tmj
temporal- squamous portion
mandible- condyloid process (condyle)
what are the unique features of tmj?
complte articular disc
two joint cavities
soft connective tissue articulating surfaces
what happens at 8 weeks embryologically for tmj
blastema or rudiments of tmj and site of condylar cartilage appearance
no cavitation`
when does cavitation of lower joint cavity occur?
third month in utero
what cartilage is the condyle composed of?
hyaline cartilage
growth site of the mandible
what kind of growth occurs between articular connective tissue surface and condylar cartilage?
appositional growth
at lower end, cartilage is mineralized, resorbed and replaced by bone tissue
how long does the condylar cartilage remain for?
until age of 25 when it is replaced by compact bone tissue
appearance of 2 ossification centers of mandible
sixth week iu
osseous union of mandibular halves
end of 1st year
appear of blastema (rudiments) of tmj
eighth week iu
cavitation within blastema of tmj
third month iu
replacement of condylar cartilage by compact bone
25 year
what does the tmj blastema form?
condylar cartilage
articular disc
two joint cavities
soft tissue articular surfaces
