mandible and TMJ

Question 1

Define Endochondral bone formation

Answer 1

*Mesenchyme is first converted into
Cartilaginous template which then is converted into Bone
*long/short bones

Question 2

define Intramembranous bone formation

Answer 2

membrane is formed by mesenchymal condensation followed by differentiation into osteoblasts

• new bone is directly formed in membrane
• most flat bones

Question 3

what bones are endochondral and what are intramembranous?

Answer 3

• Endo= all bones of skeleton below base of skull EXCEPT clavicles
• Intramembranous= cranial bones, mandible and clavicle

Question 4

Intramembranous ossification steps

Answer 4

1) mesenchymal cells group into clusters, ossification centers form
2) secreed osteoid traps osteoblasts, which then become osteocytes
3) trabecular matrix and periosteum form
4) compact bone develops superficial to the trabecular bone, and crowded blood vessels condense into red marrow

Question 5

What arch forms the mandible? what cartilage is it formed from? ossified in?

Answer 5

arch 1

• originally, meckel’s cartilage appears that than forms hyaline cartilaginous tissue
• MC is surrounded by thick perichondral fibrous mesenchyme capsule/membrane that the mandible is OSSIFIED in

Question 6

Does Meckels cartilage have a direct contribution to the developing mandible?

Answer 6

No. has a close relation to the developing mandible but makes no direct contribution to it

Question 7

what is the mandibular symphysis?

Answer 7

*where the distal ends of meckels cartilage meet; but are separated by a fibrous symphysis
(ossification of this takes place during 1st year)

Question 8

The intermediate portion of the MC _____ in mammals

Answer 8

degrades

Question 9

the most posterior portion of meckels cartilage have chondrocytes that transform into fibroblasts to form?

Answer 9

sphenomandibular ligament

* after resorption of the cartilaginous matrix

Question 10

meckels cartilage is surrounded by a perichondrium composed of?

Answer 10

fibrous mesenchymal cells

Question 11

Mesenchymal cells then differentiate into chondrocytes and organize into ______ ______ _____ prior to any sign of ossification in the mandible

Answer 11

bilateral rod-shaped cartilage

Question 12

The proximal end of meckels cartilage by the tympanic cavity of middle ear is surrounded by?

Answer 12

the forming petrous portion of temporal bone

Question 13

the dorsal (proximal) end of MC forms two?

Answer 13

auditory ossicles: Malleus and Incus

Question 14

Where is the third auditory ossicles formed from?

Answer 14

Reichert’s cartilage in 2nd pharyngeal arch

Question 15

The dorsal/proximal MC is lost by 24 weeks, but its fibrocellular capsule transforms into?

Answer 15

anterior malleolar and sphenomandibular ligaments.

Question 16

distal region of mandible undergoes _______ ossification to form the symphysis and the middle part undergoes?

Answer 16

• distal= endochondral-like
• middle (largest)= intramembranous ossification
• proximal= endochondral ossification

Question 17

The proximal region of the

mandible is what type of cartilage and has what type of ossification?

Answer 17

The proximal region of the mandible is classified as secondary cartilage and is formed by endochondral ossification

Question 18

what is ectomesenchyme made of?

Answer 18

neural crest cells

Question 19

mandibular ectomesenchyme MUST interact with what BEFORE primary ossification can occur?

Answer 19

MUST interact with epithelium of the mandible arch as well as induction by neurotrophic factors

Question 20

What happens to meckels cartilage between the lingula and canine? What about below and behind incisor?

Answer 20

• disappears

* becomes ossified and incorporated with mandible if below/behind canine

Question 21

How does mandibular ossification grow medially?

Answer 21

below the incisive nerve

Question 22

How does mandibular ossification grow ventrally?

Answer 22

around the mental nerve to form the mental foramen

Question 23

How does mandibular ossification grow upwards?

Answer 23

between the nerve and Meckels cartilage
*the incisive edge is contained in a groove of bone formed by the lateral and medial plates which are united beneath the nerve

Question 24

How does mandibular ossification grow forwards?

Answer 24

towards the middle line where it comes into close relationship with the similar bone of the opposite side, but from which it is separateed by connective tissue

Question 25

How does mandibular ossification grow backwards?

Answer 25

produces at first a trough of bone in which lies the inferior dental nerve and muchlater the mandibular canal is formed

Question 26

ossification of the mandible stops where?

Answer 26

at the site of future lingula