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.

INTRODUCTION

The skull and jaws at birthAt 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.

BONES IN SEPARATE COMPONENT PARTS

BONES WIDELY SEPARATED FROM NEIGHBORING BONES

RELATIVE SIZES OF THE FACE AND THE CRANIUM

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.

RATES OF GROWTH FROM BIRTH TO ADULT

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 .

GROWTH RATE OF THE CRANIUM

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 asmall 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.

GROWTH RATE OF THE FACE

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:

MECHANISMS AND AREAS OF GROWTH

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 between normal individuals both in growth and in thefinal form and size of the head, quite apart from the effect of anypathological conditions.

The different ethnic groups of mankind have a tendency to exhibit certain broad patterns of form of the skull and jaws although such patterns are often overshadowed by individual variation.

Variation in skull and jaw size and form between individuals is so common and so well known. occur by several reasons.

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Done byIsraa Awadh