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1. GROWTH THEORIES
It is strongly believed and understood that growth is
strongly influenced by genetic factors. Although genetic factor
is one of the main factors affecting growth a variety of other
factors like environmental factors. In the form of nutritional
status, degree of physical activity, health or illness etc. may
also contribute normal growth. Great studies have been made in
recent years in improving the understanding of growth control.
What exactly determines the growth of the jaws however
remains unclear and continues to be a subject of intensive
research.
A number of theories have been explained in connection
with growth of craniofacial structures. These include:
 Level of growth control: sites Vs centers of growth.
 Cartilage as a determinant of craniofacial growth.
 The functional matrix concept.
 Genetic theory.
 Sutural theory.
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2.  Van Cimborgh’s theory.
The major difference in the first three theories mentioned
in the location at which control is expressed.
In the first theory, it implies that genetic control is
expressed directly on bone and therefore its focus should be
periosteum. The second theory states a genetic influence on
cartilage, thus bone playing a passive role. This indirect
growth pattern is called as epigenetic. The third theory states a
genetic influence to a larger extent on tissues outside the
skeletal system, thus bone and cartilage growth occurring
mainly epigenetically in response to a variety of other factors.
GENETIC THEORY
The first factors of consideration always when growth
control is considered is the role of genetic factors. Although
role of genetics in growth and development control has long
been performed by many to have fundamental and overriding
influence its exact application is not understood fully.
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3. Contemporary researchers have failed to accept the idea that
simply gives are the exclusive determinants of all growth
parameters including regional growth amounts, velocities and
minute details of regional configuration. Fully understood of
course is that genes are basically the participants in
maintaining the operation of any given cells organells loading
to the expression of that cells particular function. For example,
functions of fibroblasts chondroblasts etc. which does their
function when needed and once saturation is reached the
function classes. Thus the genes donot play any role as a
“starter or terminator”, it is the requirement of a particular
situation which makes the cells to performed all these
functions.
LEVEL OF GROWTH CONTROL SITE VERSUS CENTERS
OF GROWTH
A clear distinction between site and centers of growth is
necessary. The site of growth refers merely to a location at
which growth occurs and center of growth is a location at
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4. which independent (genetically controlled) growth occurs. All
the centers of growth are also the sites but not the reverse is
true.
The major support for the theory that the tissues form
bone carry their own stimulus with them came from the
observation that, the all pattern of craniofacial growth is
relatively constant. This constancy of growth was interpreted
to mean that major sites of growth were also the centers.
Particularly the sutures between the membranes bone of
cranium and jaws were considered growth centers along with
sites of endochondral oscification in the cranial base and at
mandibular condyle.
Growth in this view, was thus the result of expression at
all these sites determined genetically. Thus growth at maxilla
was explained to be the result of pushing apart due to growth in
the midline along the sutures.
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5. If this theory was correct, growth at the sutures should
occur largely independently of the environmental factors and it
would not be possible to change the expression of growth at
sutures very much.
This theory was a dominant theory of growth till 1960’s
and a variety of drawbacks were explained.
It is known, at present that sutures and periosteum to a
larger extent are not the primary determinants of growth, in
craniofacial region.
This was concluded by the fact that:
a) When an area of sutures between two facial bones is
transplanted to another location (ex: to a pouch in the
abdomen) the tissues does not continue to grow. This
indicating lack of innate growth potential in sutures.
b) Secondly, growth at sutures is influenced by a number of
outside factors. Ex: if cranial or facial bones are pulled
apart, the new bone fills in and thus enlargement of bone
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6. is seen. If the sutures are compressed, the growth at
sutures is impeded thus reducing the bone size than
normal.
This implies that the sutures are the areas that react to
and not the primary determinants of growth.
c) Growth takes place in untreated cases of cleft palate even
in the absence of sutures.
d) Microcephaly and hydrocephaly raised doubts about
intrinsic, genetic stimulus of sutures.
CARTILAGENOUS THEORY CARTILAGE AS A
DETERMINANT OF CRANIOFACIAL GROWTH
This theory was put forward by James Scott in 1969.
according to this theory the primary determinant of growth of
craniofacial structures is the growth of cartilage. The fact
which made this theory attractive was that for many bones,
cartilage makes the growing part whereas bone merely replaces
the grown cartilage.
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7. If the cartilage growth is of primary influence the growth
of condyle in mandible acts as a pacemaker for growth of that
bone and remodeling of ramus and other surface changes could
be viewed as secondary to cartilage formation.
Growth of mandible in this regard can be explained by
imaging it like a diaphysis of long bones bent into horse shoe
shape with cut epiphysis at the ends exposing the cartilage that
represents condyles.
Epiphysis
Diaphysis bent into horse shoe shape
If this is a true situation then condyles should act as
growth centers behaving basically as a epiphyseal growth
cartilage.
Growth of maxilla although is difficult to explain is not
impossible. Although maxilla does not contain any cartilage.
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8. The nasal septum contains cartilage and nasomaxillary complex
grows as a single unit.
Proponents of this theory according to the study of R.D.
Latham (1969) hypothesize that cartilaginous nasal septum acts
as a pacemaker for the growth of other aspects of maxilla.
The location of nasal septal cartilage is such that its
growth brings about a forward and downward pushing of
maxilla thus opening the sutures. Now the secondary (passive)
growth of bone at sutures occurs thus resulting in net increase
in the size of maxilla.
Two types of tests have been carried out to test the
effectiveness of this theory. One by transplanting the cartilage
to some other part of the body and secondly by removing the
cartilage and then assessing the growth occurring in bones.
Coprey and Duterloo (1986) stated that not all the
cartilages act similarly when transplanted. If a piece of
epiphyseal plate is transplanted to a new state or culture, it
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9. continues to grow normally indicating presence of an innate
potential in the cartilage to grow. It seems that it is very
difficult to get cartilage from synchondrosis at cranial base
during their developmental stage. Thus the results of growth of
cartilage from synchondrosis is not as good as the growth of
cartilage in case of epiphysis transplantation.
Ronning (1966) observed a very little or no growth of
mandibular condyle cartilage when transplanted to other areas
of the body or culture media.
The second group of experiment were to test the removal
of cartilages from their developing sites and testing for growth
disturbance. Many studies have shown that the removal of
cartilage from their sites of function drastically affects the
growth of related bones. Sarnet (1976) in his experiment on
rats has shown a significant reduction in the growth of maxilla.
Another support to this experiment is a reduced midface
development as a whole due to surgical removal of nasal
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10. septum in humans at an earlier stage (due to a variety of
reasons like severe trauma).
A depressed growth of mandible in case of children
suffered from trauma during childhood is next supporting
factor due to impaction condylar cartilage.
Thus is appears of that epiphyseal cartilage and the
cranial base synchondrosis can act as independently growing
centers as can nasal septum. Thus proving cartilage to be one
of the primary determinant of growth.
FUNCTIONAL MATRIX THEORY OF GROWTH
This theory of growth was put forward by Melvin Moss in
early 1960’s. The concept of this theory is that if neither bone
not cartilage were the determinants for growth of craniofacial
complex then it would appear that the control would have to be
lying in adjacent soft tissues. According to this theory neither
mandibular condylar cartilage, nor nasal septal cartilage are the
determinants of jaw growth. Instead he theorizes that growth of
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11. facial skeleton occurs in response to functional needs and is
mediated by soft tissues in which the jaws are embedded. In
this conceptual view soft tissues grow and both bone and
cartilage react.
The theory can also be explained by the growth of
cranium in response to growth of brain. The pressure exerted
by growing brain causes saparation of sutures of the cranium
thus inducing growth at the sutures thereby enhancing the
increase in the size of cranial bones. The classical examples
being size of cranium in case of microcephaley and
hydrocephaly. In microcephaley the growth of brain being less
than normal resulting in its smaller size.
This inturn results in a disturbed growth of cranium
resulting in smaller cranium than normal. The opposite can be
explained in case of hydrocephaly where the reabsorption of
C.S.F. is disturbed resulting in accumulation of CSF in an
abnormal amount in cranium. This in turn causes on increased
intracranial pressure leading to suppuration of cranial bones.
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12. This also induces thus the bone deposition at the sutures. Thus
although brain size is small, the fluid collected along with
brain acts as functional matrix for the development of a larger
cranium.
The next example is the size of orbit relating to the size
of the eyes. In case of large eyes the corresponding orbital size
is increased and opposite for smaller eyes. Thus eyes act as
functional matrix for the growth of orbits of particular size.
In general the functional components according to this
theory are divided into:
1. Functional matrix component.
2. Skeletal unit.
All the tissues organs and spaces taken as a whole,
comprise the functional matrices whereas the skeletal tissues
associated with a particular matrix forms skeletal unit.
The changes in their size, shape including operational
activity is due to the activity of their functional matrix.
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13. SKELETAL UNIT
All the skeletal tissues associated with a single function
are called as “The skeletal unit”. This may be comprised of
bone, cartilage and tendenous tissue, when a bone is comprised
as a number of continuous units, these units are called as
“microskeletal units”.
Example, mandible has several microskeletal units like
coronoid, angular, alveolar, condylar process ramus and body.
Maxilla is composed of orbital pneumatic alveolar palatal,
basal microskeletal units.
When adjoining portions of a number of bones unit to
perform a single function they are called as macroskeletal
units. Ex: entire enoberanial surface of cranium.
FUNCTIONAL MATRIX
The functional matrix is composed of muscles, glands,
vessels, nerves and functioning spaces. This matrix is divided
into:
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14. a. Capsular matrix.
b. Periosteal matrix.
a. Periosteal Matrix: Periosteal matrices act directly and
actively on their related skeletal components. Alterations
in their functional demands produces a secondary
transformation of size and shape of their skeletal units.
This is brought about by selective resorbtion and
deposition. The periosteal matrices include muscles,
vessels, glands nerves etc.
b. Capsular Matrix: According to capsular matrix theory
the capsular matrices act indirectly and passively on their
related skeletal structures thereby bringing about the
necessary changes in these skeletal components which are
embedded, grow and maintained in them.
The facial bones move and expand in response to the
growth of their capsule. This kind of growth is not brought
about by deposition and resorbtion.
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15. The two capsules of important are neurocranial capsule
and orofacial capsule. Ech of these capsules is an envelop
which contains a series of functional cranial components
(skeletal units and related skeletal matrix) which as a whole
are sandwiched between two covering layers. In case of
neurocranial capsule the layers include skin and dermates and
in case of orofacial capsule, it includes skin and mucosal
membranes.
The neurocranial capsular surround and protects brain,
leptmininger and C.S.F. which are the functional matrices of
cranium whereas the orofacial capsule surrounds and protects
esopharyngeal structures.
Thus the function matrices have an major role in
predicting the growth of craniofacial skeleton.
VAN LIMBORGH’S THEORY
A multifactorial theory was performed in 1970 by Van
Limborgh. According to him the factors explained by all
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16. previous theories were insufficient yet contain elements that
cannot be denied. Van Limborgh explained the growth process
in a view that combines all three existing theories.
He suggested five factors that he believed to control the
growth.
a. Intrinsic genetic factors:
They are the genetic control of skeletal units themselves.
b. Local epigenetic factors:
Bone growth is determined by genetic control originating
from adjacent structures like brain eyes etc.
c. General epigenetic factors:
They are the genetic factors determining growth from
distant structures e.g. growth hormone, sore hormone.
d. Local environmental factors:
They are non genetic factors from local area caries –
habits, muscle forces etc.
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17. e. General environmental factors:
They are general non genetic factors influencing growth
which include – nutrition, oxygen etc.
The views expressed by Van Limborghs can be
summarized as:
a. Chondrocranial growth is mainly controlled by intrinsic
genetic factors.
b. Dimensional growth is controlled by any few intrinsic
genetic factors.
c. Cartilagenous part should be considered as a growth
center.
d. Sutural growth is controlled mainly by influences arising
from skull cartilages and other adjacent skull structures.
e. Periosteal growth largely depends upon growth of
adjacent structures.
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18. f. Sutural and periosteal growth are additionally governed
by local non-genetic environmental influence.
Thus a variety of factors other than genetic factor as a
major determinant play important role in basic growth is
development.
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