Formation of the TMJ and mandible

Question 1

ossification centers

Answer 1

initial appearance of bone tissue in the area where each of the 206 bone organs of the body form

Question 2

how many bones in the adult skull?

Answer 2

22 (1 mandible and 2 maxilla)

Question 3

what environments can ossification centers appear in?

Answer 3

mesenchyme called intramembranous bone organ development OR

within cartilage model called endochondral bone organ development

Question 4

how many ossification centers in bone?

Answer 4

varies from bone to bone
(2 intramem in each the mandible and maxilla)
ex. femur has 5 endochondral ossification centers

Question 5

mixed ossification center

Answer 5

have intramembranous and endochondral ossification centers

ex. temporal bone

Question 6

growth sites

Answer 6

addition of bone tissue to bone organ
ex of sites - periosteum, endosteum, haversian and volkman canals , areas of growth sites for mandible is cartilage tissue
AND THE PDL (forms tissue, not just holding tooth in place)

Question 7

where does bone tissue form?

Answer 7

intramembranous bone tissue - highly vascularized CT

Question 8

any compact bone in an embyro?

Answer 8

no, only spongy

Question 9

can bone grow interstitially?

Answer 9

no, but cartilage can

Question 10

why do you want a removed tooth to fill with blood?

Answer 10

you want it to clot because then osteogenic tissue can come in and replace the open space with bone

Question 11

what is the main vascular supply for haversian and volkmans canals?

Answer 11

PDL

Question 12

meckels cartilage

Answer 12

paired, one in each mandibular process of branchial arch 1

Question 13

meckels cartilage role

Answer 13

1. temporary skeleton of the mandibular process of branchial arch 1
2. temporary attachment for mm. that will attach to the mandible
3. each serve as a model for 2 ear ossicles (malleus and incus)
4. site of ligament appearance (anterior malleus and sphenomandibular)
5. temporary anterior lingual plate of the mandibular halves
6. enclosed growth sites at the chin (grow mandible ant.)

Question 14

what is the fate of meckels cartilageS (from inner ear cavity to chin)?

Answer 14

1. endochondral ossif centers for 2 ear ossicles (proximal)
2. undergo retrogressive chnages and BECOME 2 ligaments (soft tissue) **in the proximal and middle
3. 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
   * *****ossification centers of ear ossicles and growth site for mandible halves

Question 15

when do the two halves of the mandible come together and what is it called?

Answer 15

osseous union 1 year postnatal

Question 16

development of the mandible

Answer 16

• beings in the 6th embyronic week (same time primary buds of the mand centrals forms)
• arises from 2 bilateral ossification centers within mesenchyme tissue lateral to meckels cartilage
• grows anteriorly through distal portions of meckels cartilage (lingual plate, growth site) and grows posteriorly from the facial plate to incorporate the condylar cartilage (growth site)

Question 17

does the condylar cartilage arise from meckel’s cartilage?

Answer 17

no

Question 18

where do the mandibular ossification centers appear?

Answer 18

in the area where the inf. alveolar nerve branches into the mental and incisive nerves
**future site of mental foramen

Question 19

where do the ossification centers grow towards?

Answer 19

posteriorly to TMJ and anteriorly to midline of the chin where the two halves approach eachother

Question 20

what is the fate of the distal ends of meckels cartilage?

Answer 20

MC enclosed and replaced by bone to become ant. lingual plate of the mandible
**histologically the cells of the cartilage next to the bone start to die out)

Question 21

joint/articulation

Answer 21

place of union or junction between 2 or more bones of the skeleton

Question 22

synarthrosis

Answer 22

permits little or no mobility (fibrous and suture joints)

ex. maxillary bones

Question 23

amphiarthrosis

Answer 23

permits slight mobility (cartilaginous joints)

ex. pubic symphisis

Question 24

Diarthrosis

Answer 24

permits a variety of movements (synovial joints)

ex. TMJ

Question 25

Ginglymaarthrodial joint

Answer 25

dual compartment structure (hinge and sliding joint)

Question 26

gomphosis joint

Answer 26

binds tooth to socket

Question 27

most moveable joints have what features?

Answer 27

one joint cavity, imcomplte disc and cartilage articular surfaces
ex. elbow

Question 28

TMJ

Answer 28

• 2 bones: squamous portion temporal and condyloid of the mandible
• has a complete articular disc that forms before the 2 cavities
• soft CT articulating surfaces

Question 29

when does the TMJ start formation?

Answer 29

8th week the blastema starts and the articular disc is present but not cavitation

Question 30

Condylar cartilage

Answer 30

lasts until age 25, where it is replaced by compact bone tissue. NOT an ossification site because adding and taking away

• *like a growth disc in legs
• *can tell if older then 25 by the haversian canal systems

Question 31

when does cavitation of the TMJ start?

Answer 31

3 mo. IU

Question 32

what does the TMJ blastema form?

Answer 32

condylar cartilage, articular disc, 2 joint cavities and 2 soft tissue articular surfaces