Growth centres and sites /fixed orthodontic courses

CRANIAL GROWTH
CENTRES
FACT OR FALLACY

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The term growth centre has been
widely used with skeletal growth
phenomina to the extent that it has
been used to cover up many growth
sites.
 Baume- proposed that the term skeletal
growth centre can be used to describe
places of endochondral ossification
with tissue seperating force.
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Time factor is also brought into conideration
wherein growth centre should mean a place
where the growth of a skeleton takes place for a
sufficient length of time to make a real
contribution to the increase in skeletal mass.
KOSKI has tried to examine some of these
alleged growth centres using the definition given
by BAUME as the criterion.
BAUME also defined growth sites as regions of
periosteal or sutural bone formation and
modelling resorption adaptive to environmental
influences.

SUTURES
There are two schools of thought
regarding the growth at sutures
1. Sutures are 3 layered structures having two
layers of connective tissue seperated by a single
layer of connective tissue. The connective tissue
layer acts as the proliferatng zone. Implies tissue
seperating forces in the sutural tissue.


2.Sutures are 5 layered with the 2 bones on
either side havin 2 layers of periostium with
a 5th intevening connective tissue layer.

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Question is whether the growth is primary or
secondary in nature.
Evidence in favour of dependant role appears to
be accumulating1. Trabecular pattern -changes with age
2. Removal of sutures-appears to have no effect
on growth of the skeleton.
3. Shape of sutures-determined by functional
stimulus.


4.Closure of sutures-appears to be determined
extrinsically.
5.External force application-by using clips can
actually halt the growth at the sutures.
6.Parrallelism of sutures-only superficial
-zygomatico-maxillary sutures grow laterally
-direction of growth varies


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Conclusion
-unlikely that there are tissue seperating forces
-they are unlikely to be growth centres.


Cranial base
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Cranial base synchondrosis especially the
spheno-occipetal synchondrosis has been
considered to be a growth centre.
Evidence in favour1.structural similarity to the epiphyseal plates.
2.reaction to biochemical stimuli similar to
epiphyseal growth plates.


 Evidence against

1.no tissue seperating forces.
2.transplants


Conclusion


There seems to be no direct evidence to
support the claim that they are growth centres.


NASAL SEPTAL CARTILAGE
 The general concensus – nasal septal

cartilage provides thrusting force to
carry maxilla forward and downward
during growth.


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Evidence in favour
1. endochondral ossification -is seen
histologically.
2. vomeral-edge -is an area of proliferation
3. on palatal -surfacesresoption on nasal and
deposition on oral side.
4.excision-affects growth.
5.arrhincephalic patient-normal vertical
-retarded saggital mid
face

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Evidence against
1.excision-retards growth(may be due to
trauma,early excision does not affect)


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Conclusion
May be a growth centre in post natal life.


CONDYLAR CARTILAGE


There is a general belief that growth at the
condyles moves the mandibular body forward
and downward and this opens the space below
the cranial base into which the mandibular and
maxillary processes grow and teeth errupt.


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Evidence against
1.Structural
- Is a secondary cartilage.Latecomer, not even
from the same precursor as the as epiphyseal cartilage.
-Does not grow interstitially like epiphyseal
cartilage but appositionally from deepest layersof
connective tissue covering the condyle.
-The cells that divide are the intermediate layer cells
and not cartilage cells, these are like undifferentiated
mesenchymal cells
-Structural organization is lacking

-non hypertrophic cartilage cells-the layer is
very narow and change into hypertrophic layer
very soon.
-the whole hypertrophic area seems to be in
a state of mineralization whereas in the
epiphyseal plates only the degenerative zone is
mineralizing.
-spongiosa always seen in long bones is
lacking


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2.Functional
Resposive to mechanical stimulus
respond differentially from epiphyseal
cartilages to various hormonal and chemical
agents.
3.Transplants
only when transplanted with adjacent bone
does it grow,but even then the structure is not
maintained as beautifully.

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4. Tissue culture studies
demonstrates lack of cartilage growth
5.Surgical
bilateral condylectomy showm to have no
appreciable effect on the growth.
6.Implant
direction of growth seems to vary
considerably.sometimes upwards and
backwards and sometimes upwards and
forwards.

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FINAL CONCLUSION
The existance of growth centres have not been
demonstrated beyond doubt. We should keep an
open mind and look for explainations and
theories that agree with all well known facts.


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Growth centres and sites /fixed orthodontic courses

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