Physical Growth and Development

A. growth
B. development
C. differentiation
D. translocation
E. maturation

A. molecular biology
B. developmental biology
C. physical growth
D. behavioral development

I. Freud
II. Erikson
III. Piaget

B. normal growth patterns
C. differential growth

4. Variables affecting physical growth

A. heredity

B. nutrition

C. illness

D. surgery

E. race

F. climate and seasonal effects

G. adult physique

H. socioeconomic factors

I. exercise

J. family size and birth order

K. secular trends

L. psychological disturbances

5. Types of bone formation

A. intramembranous
B. endochondral

A. genetic

B. functional

C. hypothesis

I. genetic

II. Sicher’s

III. Scott’s

IV. Moss’

V. Petrovic’s

D. current concepts

8. Embryology

I. brachial arches

II. perioral region

III. facial proportions

IV. origin of facial malformations (syndromes and clefts)

I. tongue

II. palatal shelves

III. salivary glands

IV. adenoids

V. dentition

C. differentiation of supporting structures

I. chondrocranium

II. maxillary complex

III. bony palate

IV. mandible and TMJ

V. facial muscles

VI. muscles of mastication

9. Morphologic stages

10. Eruption of primary teeth

A. theories of eruption
B. timing of eruption / sequencing
C. problems associated with eruption

11. Exfoliation of primary teeth and eruption of permanent teeth (see also Lecture 6: Dental Anatomy and Anomolies)

A. theories of exfoliation and eruption
B. timing of exfoliation and eruption
C. problems associated with exfoliation and eruption

12. Development of occlusion

A. classification of occlusion

I. primary dentition

II. permanent dentition

B. Primate Space
C. Leeway Space
D. problems associated with development of occlusion

E. third molars

DEFINITIONS

Growth: normal dimensional changes in the amount of living substance that is measured in units of change per units of time. Does not necessarily have to be increase in size. Ex: Thymus gland after puberty decreases.

Development: all the naturally occurring unidirectional changes in the life of a species from its existence as a single cell to its elaboration as a multifunctional unit terminating in death. Ex: the human body.

Differentiation: the change from generalized cells or tissues to more specialized units during development. It is change in quality or kind. Ex: the human face.

Translocation: change in position. Ex: the chin point moves downward and forward.

Maturation: qualitative changes that occur with ripening or aging. Ex: the ovum.

DIVISIONS OF DEVELOPMENTAL SCIENCE

The study of growth and development is not separate from other biologic sciences but rather requires the knowledge and methods of gross and microscopic anatomy, psychology, biochemistry, physiology, genetics, anthropology, and other disciplines. There are four large divisions that this area can be divided into.

Molecular Biology: discovery of Ribonucleic Acid and Deoxyribonucleic Acid and deciphering the genetic code. This includes new disciplines such as molecular genetics, biophysics, and genetic engineering.

Developmental Biology: starts with the fertilized egg as a single microscopic cell and continues, by development, to become an adult comprised of millions of cells. We are more so concerned with the area of developmental oral biology. This area includes such disciplines as cellular biology, embryology, teratology, reproductive biology, and perinatal biology.

Physical Growth: the study of organ and body growth. Includes the analysis of such problems as morphogenesis, height and weight, growth rates, retarded growth, metabolic disturbances in growth, developmental physical fitness, pubescence, and morphometrics. Scientists that work in this area include pediatricians, anthropologists, endocrinologists, nutritionists, and dentists.

Behavioral Development: As the child grows physically, interaction with the environment occurs in certain expected patterns. Scientists studying in this area include embryologists, developmental psychologists, psychiatrists, pediatric dentists, physiologists, physiologic psychologists, and geneticists.

Freud: biologically determined drives. The latency period as seen in the chart below is a period of behavioral development that remains in controversy. This phase is relatively free of psychosexual conflict.

Erikson: recasted the stages in terms of the emerging personality. Psychosocial development.

Piaget: the study of cognitive development.

From: Behrman R E, Kliegman R M, Arvin A M: Nelson Textbook of Pediatrics Saunders, 15^th edition, 1996, p.33, Table 8-2.

Dental Case

A fourteen year-old arrives for her first dental examination at your office. She is standing with her mother at the front desk waiting to be checked in. You notice that you can barely see her whole face over the counter. She seems to be shorter than you expected. There are many questions crossing your mind:

Does she have a grossly abnormal growth pattern?

Has she seen a physician for diagnosis and recognition of a significant deviation from normal growth?

METHODS OF STUDYING PHYSICAL GROWTH AND DEVELOPMENT

Among the several methods of studying growth and development, there are: Opinions: ex. "I think Johnny is going to be taller than his father." Observations: ex. In 5% to 10% of U.S. children, at least one primary molar becomes ankylosed (fused to the bone) before it finally resorbs and exfoliates. Ratings and rankings: ex. tooth shape (square, tapering, and ovoid), facial form, and tooth development. Rating is a comparison with conventional accepted scales or classifications and rankings arrange data in ordered sequences according to value.

Quantitative measurements:

direct data: derived from measurements taken on a living person or cadaver by means of calipers, scales, measuring tapes, and other devices. Ex. measuring size of teeth with a Boley gauge.

indirect data: measurements taken from images or reproductions of the actual person. Ex. photos, casts or cephalograms.

Maturity indicator: those features of individual bones that can be seen in the P-A hand-wrist film and which mark their progress toward maturity.

Derived data: obtained by comparing at least two other measurements. Ex. a person’s mandible grew 2 mm between ages 7 and 8. The 2-mm was not actually measured.

Normal Growth Patterns

Rather than categorizing people as normal or abnormal it is better to think in terms of deviations from the usual and to express variability quantitatively. A given child can be evaluated in comparison to their peers on a standard growth chart.

Deviations in the growth pattern are nonspecific but are very important indicatory of disorders of growth and development.

Estimates for normal growth and development

Weight:

Weight loss in the first few days = 5-10% of birthweight

Return to birthweight = 7-10 days

Double birthweight = 4-5 mo

Triple birthweight = 1 yr.

Quadruple birthweight = 2 yr.

Average weights = 3.5 kg at birth (7lbs. 11oz.)

10 kg at 1 yr.

20 kg at 5 yrs.

30 kg at 10 yrs.

Annual weight gains = 5 lbs. Between age 2 yrs. and puberty

Height:

1. Average length at birth = 20 in
    Average length at 1 yr. = 30 in
2. Age 3 = 36 in tall
3. Age 4 = 40 in (double birth length)
4. Average annual height increase = 2-3 in between age 4 and puberty

Head circumference:

Average HC = 35 cm at birth (13.5 in)

Increases = 1 cm/mo for the first year then 10 cm over the rest of life

DIFFERENTIAL GROWTH

Growth is not always linear and differs from person to person and from organ system to organ system.

Variability in body proportions (somatotypes):

Ectomorphs = Small mass to height ratio. Relative linear growth with light body structures.

Endomorphs = High mass to height ratio. Stocky builds with large amounts of soft tissue.

Mesomorphs = Proportionate mass to height ratio. Body builds lies somewhere in the middle of the two extremes.

Variability in body systems:

Neural = Includes the brain and the spinal cord and their coverings, the optic apparatus, the auditory apparatus. A rapid growth rate during the first 2 years, slower until age 6, very slow after that and then ceases before puberty. By age 7 years the brain is almost 95% of the adult size and function.

Lymphatic = Includes the thymus, lymph nodes and mucosal lymphatic masses (tonsils). Growth rate peaks at age 12 yrs. then begins to degenerate.

Bone = Sigmoidal growth continues to approximately age 20. Maximum rates early in life (birth to 1 yr.) and at puberty. Development of the mandible and the maxilla follow a similar pattern to neural except that full maturation is not achieved until 20 years of age or older.

Vasculature = Varied growth rates during the first 20 years.

VARIABLES AFFECTING GROWTH AND DEVELOPMENT

Heredity: The genetic aspect of physical growth can be studied using twin and family data. Differences between monozygotic and dizygotic twins are assumed to be differences due to environment. There is genetic control of the size of body parts, the rate of growth, and the onset of growth events. Not all genes are active at birth. Some only express themselves in the surroundings made possible by the physiologic growth of later years. Ex.: Minnesota Twins Study.

Nutrition: Deficiency in calories or reduced food intake results in malnutrition. Malnutrition delays growth and may affect size of body parts, proportions, body chemistry, and the quality and texture of some tissues (ex: teeth and bones). Malnutrition may also delay growth and the adolescent growth spurt. Children may revert to normal or show "catch up growth" depending on how extreme the adverse conditions were.

Illness: Systemic disease has an effect on child growth, but the plasticity of the human organism during growth is so great that the clinician must differentiate between minor and major illnesses.

Surgery

Race: Anthropologists have expressed difficulty in defining race. Some racial differences are due to climatic, socioeconomic, and nutritional differences. However gene pool differences account for the fact that North American blacks are ahead of whites in skeletal maturity at birth and at least during the first two years of life.

Climate and seasonal effects: Climate has been found to have little direct effect on the rate of growth. Growth rates are maximal in summer and minimal in winter.

Adult physique: Correlations can be found between physique and earlier development events. Ex: Taller women tend to mature later and there variations in the rate of growth associated with differing somatotypes.

Socioeconomic factors: This can be linked to nutrition. Differences seem to be linked with "class" and not necessarily income. Differences in height-weight ratios and variations in the timing of growth can be seen. Overall, this aspect remains unexplained.

Exercise: The effects of exercise on linear growth have not been proven quantitatively. Children that exercise strenuously and regularly have not been shown to grow more favorably but they have more developed motor skills and increased muscle mass.

The following are factors that were believed to be a factor in the past:

Family size and birth order: Correlation between family size and size of the individual, maturation, and their intelligence have been identified. First born usually tend to be less in birth weight, achieve less stature, and a higher I.Q.

Secular trends: Size and maturational changes in large populations are occurring. Even when race, socioeconomic level, nutrition, climate, and other differences have been controlled in samples this did not seem to change. These changes have no satisfactory and generally accepted explanation. There seems to be a general trend towards increased height/weight with each succeeding generation. This may be accounted for by improved nutrition, reduction in frequency of debilitating illnesses, natural selection, and improved socioeconomic conditions.

Psychological disturbances: It has been shown that children experiencing stressful conditions display an inhibition of growth hormone. When the emotional stress is removed they begin again to secrete growth hormone normally, and "catch-up" growth is seen.

TYPES OF BONE FORMATION

Intramembranous: Undifferentiated mesenchymal cells of the membranous connective tissue change to osteoblasts and elaborate osteoid matrix. This matrix or intercellular substance becomes calcified and bone forms. Ex: bone formed by periosteum, endosteum, sutures, and the periodontal ligament.

This is the predominant form of growth.

Fast-growing.

Occurs in areas of tension.

Constant deposition and resorption takes place.

Membrane grows outward rather than receding as bone is laid down.

The periodontal membrane works as an area of tension in converting the pressure to the collagen fibers, which attach the tooth to the bone.

Forms from mesenchymal cells.

Endochondral: By contrast this involves the calcification and ossification of hyaline cartilage, which was formed in utero from mesodermal cells.

Produced in areas of relatively high levels of compression.

Associated with movable joints and some parts of the basicranium.

Not formed directly from cartilage but invades and replaces it.

Cartilage is firm and rigid but still flexible, not calcified (ex: nose).

Cartilage grows both appositionally, by activity of the chondrogenic membrane, and interstitially, by cell division of chondrocytes and addition to its intercellular matrix.

May stay as calcified cartilage during growth (ex:articular surfaces, epiphyseal plates, and synchondroses) or transformed to bone.

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