early normal growth of the craniofacial skeleton Flashcards
What is isometric growth?
Implies progressive proportional increase in all organs and systems w time
What is allometric growth?
Describes differences in relative rates of growth between one part of the body and another
How does the body grow from fetus to adult?
6-7 weeks post fertilisation- head is nearly half of embryo
Then grows proportionally more slowly
Adults- head 1/8 of length of body
What are the mechanisms of craniofacial growth?
Skull posterior to coronal suture is derived from mesoderm
Bones anterior to suture are derived from ectomesenchyme from neural crest
2 types of bone formation but both start w coalescence of mesodermal and ectomesenchymal cells into dense groups- CONDENSATION
Condensed cells may differentiate into chondroblasts that form a cartilaginous template of bone which is then replaced by bone- ENDOCHONDRAL OSSIFICATION
Bone may be formed directly in condensation- INTRAMEMBRANEOUS OSSIFICATION
Most organs grow by INTERSTITIAL GROWTH- cell division and matrix proliferation
Mineralised matrix of bonds prevents interstitial growth
Bones grow by addition of new material onto existing surfaces- APPOSITIONAL GROWTH
Bones developing by ECO don’t have same limitations as cartilage can grow by interstitial growth
REMODELLING- Surface deposition (osteoblasts) and resorption (osteoclasts)
During growth periods almost bone undergoes remodelling
GROWTH SITES- surfaces/cartilages where large amounts of growth take place
What causes growth of craniofacial skeleton?
General- hormonal, nutritional, genetic and socioeconomic influences
Local- growth pattern (somatic, neural), caspsular matrices (enclosed tissues) and periosteal matrices (muscle attachments, teeth)
What is the skull at birth like?
Calvaria proportionally large- reflects early cerebral maturation
Facial skeleton small (1/8 of cranium)
Adults would be half of cranium
Ossification incomplete in many sites- FONTANELLES- allows compression of skull and brain growth (closes 12-18 months after birth)
Smallness of face at birth due to rudimentary stage of development of mandible/maxilla
What is the cranial base?
Formed from cartilaginous precursor- before other elements of skull
Bones formed by endochondral ossification
In between bones are cartilaginous joints (remnants of precursors)- SYNCHONDROSES
Growth can occur at the synchondroses
Growth in base results in most of cranial lengthening
Most important site of growth- spheno-occipital synchodrosis (continues till 15-18yrs)
Elongation of cranial base allows room for elongation of maxilla to accommodate 2nd and 3rd permanent molar teeth
What is the cranial vault (calvaria)?
Bones are formed by intramembraneous ossification
Follows neural growth pattern which is rapid prenatally
Rapidly in first year then slower rate until 7th year
In first year- appositional growth accompanied by remodelling for altering curvatures
Fontanelles gradually close via ossification of bones which meet but don’t fuse- SUTURES (essential growth sites)
Sutures fuse in maturity
What is the face?
Formed by intramembraneous ossification
Occurs over long period
Orbital and upper nasal cavity growth- deposition of bone at sutures
Deposition occurs on facial aspect of sutural junctions
Maxilla is carried downwards and forwards by expansion of orbits and nasal septum + sutural growth
Increasing width- ~Frontal suture ~Inter nasal suture ~Midpalatal suture ~Symphysis menti
How does the maxilla grow?
Deposition at inner aspect
Resorption at outer aspect
However, rapid deposition at tuberosities so maxilla translocated forwards
Deposition posteriorly is greater that resorption anteriorly so there is growth also
The upper aspect of bones in the floor of the nasal cavities are resorbed
Bone is deposited on the oral surface of the palate
Direction of growth of the maxillary arch is downwards
How does the mandible grow?
Embryo- mandible forms by IMO
Ossification occurs around mental, incisive and inferior alveolar nerves
Ramus is formed by rapid backwards spread of ossification
Secondary cartilages appear in mandible (growth sites) and produce bone via ECO
Condylar cartilage is one of the main sites of bone deposition- active throughout growth period to maturity
As cartilage grows its replaced inferiorly by bone
Narrow zone of growth cartilage remains beneath articular surface of condylar head
Primary dentition erupts- mastication- stimulates muscles- increases size of their attachment sites to mandible- angle of mandible must be altered so occlusal surfaces of upper and lower teeth are parallel
Position of TMJ is altered by growth in lateral cranial base
Resorption along anterior border/deposition along posterior border in ramus to adjust condylar head position
Growth of condylar cartilages elongates rami
How do the facial soft tissues grow?
Mostly during puberty
May mask/enhance hard tissue changes below
NOSE- grows downwards and forwards until at least early adulthood, seems to be independent of skeletal growth (average yearly increase 1-1.3mm, no gender difference)
LIPS- grow more than skeletal lower face, lower more than upper
Upper lip- rapid from 1-3 years, slows from 3-6 years, then increases til 15 years
Increase in lip thickness at vermilion border proportional to increase in lip length
CHIN- increased chin projection due to mandibular growth
