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Growth and Development
Dr.Omar S.M.J.Ali
PhD Orthodontic
Growth and Development
• Growth : increase in size or number
•Development : an increasing degree of organization
Growth is largely an anatomic phenomenon,
whereas development is physiologic and behavior
Growth
increase in size
1 cm3
8 cm3
Development
Change in the ratio
1 cm3
1 cm3
Human G & D
1
cm3
8 cm3
GROWTH
Growth may or may not bring
development
E.g.: A child may growth fat but
becoming fat no functional
improvement may take place
DEVELOPMENT
Development is possible without
growth.
E.g.: A person may not gain height,
weight or size but can functional
improvement in other aspects.
In fetal life,
• at about the third month of
intrauterine development,
the head takes up almost 50 % of
the total body length
In contrast, the limbs are still
rudimentary and the trunk is
underdevelope
By the time of birth,
• the trunk and limbs have grown faster
than the head and face, so that the
proportion of the entire body devoted
to the head has decreased to about
30%.
• Changes in proportions of the head and face during growth At
birth, the face and jaws are relatively underdeveloped compared
with their extent in the adult. As a result there is much more
growth of facial than cranial structures postnatally
Teeth are unique: no change or growth
after eruption.
The Nature of Skeletal Growth
• At the cellular level, there are only three
possibilities for growth;
1. Hypertroph: an increase in the size of
individual cells
2. Hyperplasia: increase in the number of the
cells
3. Secretion of extracellular material :
contributing to an increase in size independent
of the number or size of the cells themselves
secretion
HYPERPLASIA
proliferating cells
(cell division)
HYPERTROPHY
Increase in cell size
Extracellular matrix
Hyperplasia
Hypertroph
Secrete
extracellular
material
Occur in
Skeletal
growth
Growth and Development
• Hyperplasia is a prominent feature of all forms of
growth
• Hypertrophy occurs in a number of special
circumstances but is a less important mechanism
than hyperplasia in most instances
• Although tissues throughout the body secrete
extracellular material, this phenomenon is
particularly important in the growth of the
skeletal system, where extracellular material later
mineralizes.
Growth and Development
• The fact that the extracellular material of the
skeleton becomes mineralized leads to an
important distinction between growth of the
soft or non mineralized tissues of the body
and the hard or calcified tissues.
Interstitial growth
secretion
HYPERPLASIA
proliferating cells
(cell division)
HYPERTROPHY
Increase in cell size
Extracellular matrix
If the extracellular matrix is NOT mineralized,
interstitial growth may continue in soft tissues and cartilages.
Growth and Development
• Hard tissues are bones, teeth, and sometimes
cartilages. Soft tissues are everything else. In
most instances ,cartilage, particularly the
cartilage significantly involved in growth,
behaves like soft tissue and should be thought
of in that group, rather than as hard tissue.
Growth and Development
Interstitial growth
• Growth of soft tissues occurs by a combination
of hyperplasia and hypertrophy.
• These processes go on everywhere within the
tissues, and the result is what is called interstitial
growth, which simply means that it occurs at all
points within the tissue.
Growth and Development
Interstitial growth
Secretion of extracellular material can also
accompany interstitial growth, but hyperplasia
primarily and hypertrophy secondarily are its
characteristics
Growth and Development
Interstitial growth
Interstitial growth is a prominent aspect of overall
skeletal growth because a major portion of the
skeletal system is originally modeled in cartilage.
This includes the basal part of the skull as well as
the trunk and Iimbs.
Growth and Development
Development and maturation of the chondrocranium
(cartilage: light blue, bone: stippled dark blue)
A , Diagrammatic representationa t about 8 weeks
B. , Skeletal development at 12 weeks.
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Growth
Development
Hypertroph
Hyperplasia
extracellular material
Interstitial growth