Concepts of Growth and Development



Concepts of Growth and Development

Chapter 2

Contemporary Orthodontics

Proffit, 1999

Why do we study Growth and Development?

Malocclusion and dentofacial deformities occur due to variations in the normal developmental process, and should be evaluated against a perspective of normal development.

Orthodontic treatment often involves manipulation of skeletal growth, which requires understanding of the general concepts of physical growth and development

Definitions

Growth: Increase in size or number

Development: Increase in complexity

Growth: Pattern, Variability, and Timing:

Pattern of Growth reflects proportionality and refers to changes in the body spatial proportions over time.

Aspects of normal pattern:

Cephalocaudal gradient of growth: means there is an axis of increased growth extending from the head toward the feet.

2. Not all tissue systems of the body grow at the same rate. The overall pattern of growth is a reflection of the various tissues making up the whole organism.

One reason for gradients of growth is that different tissue systems that grow differently concentrated in various parts of the body.

See Scammon’s curves of growth of the four major tissue systems

The cephalocaudal gradient in the head leads to more growth of the

facial than cranial structures, and more of the mandible than maxilla.

3. Predictability: Pattern repeats. Any change is considered as an alteration in the expected changes in body proportions.

Growth: Pattern, Variability, and Timing:

One way to measure variability in growth is to compare a given child relative to peers on a standard growth chart, which is derived from large-scale studies of groups of children (See growth Charts)

Growth charts could be used in two ways:

1. To determine the location of the child relative to the normal population

To follow a child over time

Growth: Pattern, Variability, and Timing:

Variability in growth arises from normal variation, influences

outside the normal experience (serious illnesses), and from

timing effect.

The biologic clocks of different individuals are set differently.

Timing variations are particularity evident in human

adolescence, especially in girls.

The onset of menstruation, often referred to as menarche,

gives an excellent indicator of the arrival of sexual maturity

Velocity vs. Distance Curves of Growth: (See figure)

Growth velocity curves for early, average, and late maturing girls: (See figures)

Because of the time and variability, chronological age often is not a good indicator of the individual’s growth status.

It is more appropriate to measure age biologically, in terms of progress toward various developmental markers (developmental, skeletal age, dental age)

Methods of Studying Physical Growth:

Measurement Approaches:

Craniometry: on dry skulls (cross sectional only).

2. Anthropomtery: on living individuals. Cross-sectional and

longitudinal. Soft tissues introduce some variability.

3. Cephalomteric radiography: more accurate, cross-sectional and longitudinal.

4. Graphically in the form of distance or velocity curves or using various mathematical transformations

Experimental Approaches using:

1. Different vital stains such as Alizarin stain.

2. Autoradiography and radioactive tracers

3. Implant radiography

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