mandible and TMJ Flashcards
Define Endochondral bone formation
*Mesenchyme is first converted into
Cartilaginous template which then is converted into Bone
*long/short bones
define Intramembranous bone formation
membrane is formed by mesenchymal condensation followed by differentiation into osteoblasts
- new bone is directly formed in membrane
- most flat bones
what bones are endochondral and what are intramembranous?
- Endo= all bones of skeleton below base of skull EXCEPT clavicles
- Intramembranous= cranial bones, mandible and clavicle
Intramembranous ossification steps
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
What arch forms the mandible? what cartilage is it formed from? ossified in?
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
Does Meckels cartilage have a direct contribution to the developing mandible?
No. has a close relation to the developing mandible but makes no direct contribution to it
what is the mandibular symphysis?
*where the distal ends of meckels cartilage meet; but are separated by a fibrous symphysis
(ossification of this takes place during 1st year)
The intermediate portion of the MC _____ in mammals
degrades
the most posterior portion of meckels cartilage have chondrocytes that transform into fibroblasts to form?
sphenomandibular ligament
* after resorption of the cartilaginous matrix
meckels cartilage is surrounded by a perichondrium composed of?
fibrous mesenchymal cells
Mesenchymal cells then differentiate into chondrocytes and organize into ______ ______ _____ prior to any sign of ossification in the mandible
bilateral rod-shaped cartilage
The proximal end of meckels cartilage by the tympanic cavity of middle ear is surrounded by?
the forming petrous portion of temporal bone
the dorsal (proximal) end of MC forms two?
auditory ossicles: Malleus and Incus
Where is the third auditory ossicles formed from?
Reichert’s cartilage in 2nd pharyngeal arch
The dorsal/proximal MC is lost by 24 weeks, but its fibrocellular capsule transforms into?
anterior malleolar and sphenomandibular ligaments.
distal region of mandible undergoes _______ ossification to form the symphysis and the middle part undergoes?
- distal= endochondral-like
- middle (largest)= intramembranous ossification
- proximal= endochondral ossification
The proximal region of the
mandible is what type of cartilage and has what type of ossification?
The proximal region of the mandible is classified as secondary cartilage and is formed by endochondral ossification
what is ectomesenchyme made of?
neural crest cells
mandibular ectomesenchyme MUST interact with what BEFORE primary ossification can occur?
MUST interact with epithelium of the mandible arch as well as induction by neurotrophic factors
What happens to meckels cartilage between the lingula and canine? What about below and behind incisor?
- disappears
* becomes ossified and incorporated with mandible if below/behind canine
How does mandibular ossification grow medially?
below the incisive nerve
How does mandibular ossification grow ventrally?
around the mental nerve to form the mental foramen
How does mandibular ossification grow upwards?
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
How does mandibular ossification grow forwards?
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
How does mandibular ossification grow backwards?
produces at first a trough of bone in which lies the inferior dental nerve and muchlater the mandibular canal is formed
ossification of the mandible stops where?
at the site of future lingula
