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DRAFT (FACIAL SKELETON GROWTH- 8) (Cranial Base: Mainly Endochondral More…
DRAFT (FACIAL SKELETON GROWTH- 8)
Cranial Vault
: Endochondral /
Mainly Intramembraneous
(less genetically programmed, adaptive)
Suture growth (Adaptive to brain growth)
Fontanelles close (2years)
But sutures remain patent until later in life
Sagittal: 25
Coronal: 27-28
Cephalocaudal gradient
Top part of body/head stop growing faster. Bottom part can continue growthing later
4y/o: Brain and cranial vault 80% adult size
10yo: 95% brain and cranial vault 95% adult size
Afterwards suture growth + remodelling
Cranial Base
:
Mainly Endochondral
More genetically controlled (Growth centre, if not genetically controlled, growth site) Laterally suture more important
Synchondroses Growth
Types:
Intersphenoid synchondrossis (Not relevant after birth)
Sphenoethmoidal synchondrosis: (Relevant until after puberty)
Spheno-occipital synchondrosis: (Relevant until age 7)
When it fuses and what age it contributes to growth
Synchondroses: temporary cartilaginous joints between bones of endochondral origin
vs epiphyseal growth plates 1) Both derived from parimary hyaline 2) Endochondral have primary chondrocytes 3) Become obliterated at maturity. Synchondroses are bipolar vs unipolar epiphyseal growth plates
Intramembraneous areas
Remodeling: Resorption in inner surface, deposition on outher
Anterior stops at age 7, Posterior continues until puberty.
Difference between growth site & centre
Centre
Growth more intrinsically regulated
TIssue separating capabilities
Eg. Cranial base synchondroses
Site
Growth secondary and compensatory in nature; respnods to extrinsic factors
No tissue separating capabilities
Eg. Periosteum...
The Midface
Growth affected by cranial vault and base
All bones except inferior turbinates are formed intramembraneously
No cartilgainous precursors
Mechanisms of growth
Apposition of bone at the sutures: Growth at circum-maxillary (Mid fact to cranial vault) + Intermaxillary Suture (Ocurs inresponse to midfacial displacement - inferior, anterior and lateral displacement
Extensive surface
remodelling
over entire nasomaxillary complex (Especially along posterior & suprior aspects)
Factors affectnig
Expansion of brain in cranial cavity
Growth of anterior cranial base
Anterior and inferior growth of nasal septum
Expansion of nasal cavity and oronasal pharynx
Translation/displacement works opposite to deposition effect OR have an additive effect. Eg Maxilla displaced downwards, but bone on anterior surface resorbts, but displacement is more so net anterior.
At age 7 : Growth of brain and eyes complete, Nasal septum decreases significantly in growth activity, significant downward and forward growth over next decade
Almost entirely by intramembranous ossification
Mandible
Intramembraneous ossification
Secondary Cartilage: Developes from periosteum of mandible
Primary Cartilage: Developes from chondrocytes
At birth: 2 Halfs separated by mental symphysis
Mechanisms of mandibular growth
Endochondral activity: Proliferation & ossification of
secondary cartilage
at condyle
Surface remodeling: Periosteal activity, differential formation and bone remodeling
Strength of muscles will cause bone in that area to develop more
Chin inactive growth site, Ramus grows higher, Body grows longer, resorption at anterior surface of ramus creates space for the molars