Mechanisms of early normal growth of the craniofacial skeleton Flashcards
isometric growth
- implies progressive proportional increase in all organs and systems with time
allometric growth -
describes the differences in the relative rates of growth between one part of the body and another
how is allometric growth shown
changes of body promotion between foetuses neonates and children and adults
what is the skull posterior to the coronal suture derived from
mesoderm
bone anterior to coronal suture derived
ectomesenchyme
where is ectomesenchyme from
neural crest
how does bone formation start (with both types)
coalescent of mesodermal or ectomeenchymal cells into dense groups/cluster
(condensation)
what happens after bone condenstiaotn
condensed cells differentiate into chonroblsts
- these from cartilaginous templates of bone§
what happens after bone templates (cartilaginous) are formed
cartilage replaced by bone (endochonral ossification ECO)
or
bone may be formed directly in the condensation by intramembranus ossification (IMO)
endochondral ossification
- cartilage is then eventually replaced by bone
intramembranous ossification (IMO)
- the bone may be formed directly in the condensation
how do most organs grow
interstitial growth
by cell division and matrix proliferation through out their structure
what prevents interstitial growth
mineralised matrix of bone
how does bone gro
addition of new material onto existing surfaces
addition of new material onto existing surfaces name
appositional growth
what can grow by interdigital growh
cartilage
and then convert to bone as it does not have the same mineral matrix
which bone developing path doesnt have the limitations of interstitial growth
endocochonral ossifiation
what is adult size and proportion of bone affected by
surface deposition
respotion
growth sites
surfaces or cartilages where large amounts of growth take place
what happens during growth periods
almost all internal and external bone surfaces undergo remodelling
factor which cause growth of craniofacial skeleton
hormonal
nutritional influences
genetic
socioeconomic
local effects which cause growth of craniofacial skeleton
growth pttern
capsular matricies
periosteal matricies
type of growth pattersn
somatic (facial skeleton follows this)
neural (cranial vault)
capsular matricies
enclosed tissues
growth of adjacent bones follows the growth of tissues they enclose
periosteal matrices
muscle attachments
teeth
proportion of skull at brith
skull is proportionally large
facial skeleton mall
what is smallness of face at birth due to
rudimentary stage of development of md and mx (as teeth are unerupted)
what does large size of calvaria reflect
early cerebral maturation
- brain is developing during utero so therefore needs to be fairly large
areas that ossification is incomplete are called
fontanel
- soft areas
what are fontanel areas needed fro
so there can be an overlap of bones during birth
- easing passage through birth canal
what happens to after fontanel after birth
filled with bone
most growth post natal growth of skull occurs
facial skeleton
how is the cranial base formed
Cartilage is laid down and then replaced by bone
The cartilaginous precursors of the cranial base appear before other elements of the skull
The bones of the cranial base are formed by the ECO
- in between the bones of the cranial base are cartilaginous joints (remnants of the precursors) – synchondroses
- Growth can occur at these sights
what are synchondroses
between the bones of the cranial base are cartilaginous joints (remnants of the precursors
where is the most important site of growth in the cranium
sphenoid occipital synchondrosis
what does elongation of the cranial base allow for
room for elongation of the maxillae to accommodate 2nd and 3rd molars
how are bones of the cranial vault formed
IMO
- growth of the vault follows the neural growth pattern of the enclosed brain which is rapid prenatally
- Growth is till rapid in the first then slower until the 7th year
in the first year grows primarily by appositional hrowt
fontanelles
- gradually closed by the ossification of bones around them
- Bones meet but do not fuse
- they remain separated by fibrous joints or sutures, which are essential growth sits in the immature skull
- sutures will fuse in maturity
when do sutures fuse
in maturity
how are facial bones formed
imo
how is orbital and upper nasal growth achievers
deposition of sutures
how is the maxilla formed
carried down and forwards by expansion of the orbits and nasal septum by sutural growth
how many frontal bone adult vs children
adult have 1
children there are 2 fused by a frontal suture
growth vectors adult vs children
adults mainly forward
children mainly downwards
how does the maxilla grow
deposition on inner aspect of alveolar etch
respotion on outer
suggest posterior growth
- rapid bone deposition around maxilla tuberosities results in maxillary complex being translocated forwards
(growth and translocation)
how is the mandible formed embroyinically
IMO
Ossificcation occurs around mental insivive and inferior alveolar nerves (in md canal)
steps of mandible formation in embryo
- ramus is formed by rapid backward spread of ossification
- secondary cartilages appear in the mandible, form secondary to the bone (they are not primary cartilages as these are formed in the pharyngeal arches)
- secondary cartilages are growth sites, producing bone by ECO
where is the main site of deposition in the mandible
condylar cartialge
- active throughout growth period to maturity
- as cartilages grows it is replaced inferiorly to bone
- narrow zone of growth cartilage persists beneath the articular surface of the condylar head
what is not present at birth in md
alveolar process
steps of md formation after birth and teeth
1) dentition enables infant to chew food
2) stimulates development of muscles of mastication
3) increases size of their attachment sites to mandible
4) angle of mandible must be altered so that occlusal surfaces of upper and lower teeth are parallel
5) The position of the TMJ is altered by growth in the lateral cranial base (mandibular/glenoid fossae) i.e. as the shape of the skull changes the TMJ needs to alter with this by…
6) selective resorption and deposition in the ramus adjusts the position of the condyalr head
7) growth at the condylar cartilages elongates the rami of the mandible
8) length of the ramus and the body is also increased by bone deposition along the posterior border of the ramus (resorption along the anterior border)
9) increase in length accommodates eruption of the permanent dentition
what can soft tissues do
mask or enhance tissue changes
average growth of nose
1.1/3mm
lips growth
lower are than upper
- upper lip shows rapid increase in length @1-3 yrs, slows 3-6 then increases up to 15 years
what is proportional in lip size
thickness at vermillion border proportional to increase at lip length
chin
increased protection in males during growth
md growth rather than soft tissue change
what accommodates eruption of permanent dentition
lengthen of maxilla
why does the md grwo
accomodate perimament
maintain aloghtment of TMJ
keep upper and lower teeth aligned
