Postnatal growth and development

Most orthodontic treatment
at the present time is carried
out during the growth
period, between the ages of
10 and 15 years. The
occlusion and position of the
teeth is also established
during the growth period,
and change after growth has
finished are of relatively
minor degree.

The skull and jaws at birth
At birth, the skull is far from being merely a small
version of the adult skull. There are differences in
shape, in proportion of the face and the cranium
and in the degree of development and fusion of the
individual bones.

At birth, the head forms about one quarter of the total height of the
body. In the adult the head forms about one eighth of total body height.
Therefore between birth and maturity the body must grow faster, in
proportion to size, than the head.

While the total growth of the head from birth to
maturity is proportionately less than that of the
rest of the body, the head itself does not grow
at a constant rate, the two main components of
the head, that is the cranium and the face,
differ in their relative proportion at birth and at
maturity, and therefore they must grow at
differing rates, neither of which is constant. The
two components can be considered separately.

The cranium, which has
grown rapidly before birth,
continues to grow rapidly
up to about 1 year of age,
Thereafter the growth rate
decreases, and by about 7
years of age the cranium
has reached some 90% of
its final volume There is
then a slow increase in size
to maturity .

The growth rate of the eyes, and consequently of the eye
sockets, follows a similar pattern.
Thus the infant, by comparison with the adult, appears to have a
small face, with large eyes, large cranium and retrusive nose.

The growth rate of the face, which is
highest at birth, falls sharply and
reaches a prepuberal minimum.
Growth rate then increases to a peak
at puberty, declining again and tailing
off until growth ceases in late
teenage.
Facial growth is normally associated
with eruption of the primary dentition
between 1 and 3 years of age and of
the permanent dentition between 6
and 14 years of age.

 Studies of dental arch have suggested that increase in size
of the dental arches is particularly associated with tooth
eruption.

 studies of growth of the head have shown that during the
same period the total length and height of the jaws
increases and the face is progressively positioned
downward and forward in relation to the cranium

 They also found a close relationship between
maximum puberal growth and maximum condylar
growth and suggested that mandibular growth
continues on average about 2 years longer than
maxillary growth.

 This difference in growth between the two jaws may
be important in orthodontic treatment planning

While the possibilities for how the skull grows can
be clear , the question of where growth actually
takes place?

- Bone, unlike most other tissues, cannot grow
simply by interstitial division of its living cells to
give increasing size.

- There are three main mechanisms of bone
growth, each of which plays its part in the growth
of the skull and jaws:

 Cartilaginous growth: the growth of cartilage by cell
division, with progressive conversion to bone by ossification .

The areas of the skull where cartilaginous growth is possible
are mainly in nasal septum and at the head of the mandibular
condyle.
 Growth of the nasal septal
cartilage would bring the nose
forward from its original
position under the front of the
cranium.

 Growth of the mandibular
condylar cartilage would
increase the total length and
height of the mandible.

 Sutural growth: the apposition of bone in the
area of the sutures between adjacent bones.
 The bony sutures of the head are
such that sutural growth would
be capable of increasing the size
of the head in all dimensions.

 It has been suggested that sutural
growth move the face in a
forward and downward direction
in relation to the cranium.

 Also sutural growth is active in
bringing the bones into close
proximity.

 Periosteal and endosteal growth: the apposition
of bone under the periosteal membrane and at the surfaces
of the cancellous spaces within the bone.
- The apposition of bone on the
periosteal surfaces would obviously
enlarge the head in all dimensions
cause the bones to be excessively
thickened and therefore
concomitant resorption of bone is
necessary in order to obtain the
appropriate thickness and strength.

- This process called bone
remodelling ; which often involves
resorption of bone from the outer
surface and apposition of bone on
the inner surface.

Endosteal resorption and addition
of bone from within the cancellous
spaces is also necessary to maintain
the appropriate thickness of the
cortical layer of bone.

generally thought that: this method of growth is
the most important part in the growth of the head
because its the most active in the skull and jaws after
the first few years of life, when cartilaginous and
sutural growth slows.

Variation

Normal variation RACIAL VARIATION INDIVIDUAL VARIATION

Variation exists The different ethnic
between normal groups of mankind
individuals both in Variation in skull and
have a tendency to
growth and in the jaw size and form
exhibit certain broad
between individuals is
final form and size of patterns of form of the
so common and so well
the head, quite apart skull and jaws although
known. occur by
from the effect of any such patterns are often
several reasons.
pathological overshadowed by
individual variation.
conditions.

Postnatal growth and development

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