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 8 cm3 1 cm3

Development Change in the ratio 1 cm3 1 cm3

Human G & D 8 cm3 1 cm3

GROWTH DEVELOPMENT Growth may or may not bring development E.g.: A child may growth fat but becoming fat no functional improvement may take place 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; Hypertroph: an increase in the size of individual cells Hyperplasia: increase in the number of the cells 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

Secrete extracellular material Hypertroph Hyperplasia Secrete extracellular material Skeletal growth Occur in

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 If the extracellular matrix is NOT mineralized, 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.

Growth Development Hypertroph Hyperplasia extracellular material Interstitial growth