Ortho module 1

Question 1

What are the distribution measures seen in variability of growth?

Answer 1

The range is from smallest to the largest value

The mean is the arithmetic average

The standard deviation is calculated from a mathematical formula as a way to describe the variance within the distribution

Question 2

What is the difference between growth and development?

Answer 2

Growth, most of the time, will refer to a change, almost always an increase, in size or number, generally with an anatomic reference. Occasionally, however, it will be used to indicate more of an increase in complexity than size.

Development will be used primarily to refer to an increase in complexity—especially when this carries with it an overtone of specialization and loss of potential.

Question 3

Why should a dentist know growth/development?

Answer 3

2 important reasons:

It is important to know normal patterns of growth and development in order to work with children and know what changes are normal and what changes aren’t.

It is important to understand growth in order to understand how to manipulate growth to treat developmental problems in children.

Question 4

What does growth pattern describe?

Answer 4

Growth of objects follow proportional relationship to the overall growth of a structure. (eg article of clothing becoming larger means logo grows all around in a proportional way)

Question 5

What does the cephalocaudal gradient of growth describe?

Answer 5

The proportion of total body size contributed by the head and face steadily decreases after the 3rd month of fetal life. By the time of birth, greater growth of the trunk and limbs has reduced the head to 25% of the entire body. This pattern continues, so that the head and face contribute proportionally less and less to the total body length. This relative reduction in head and face size is because the craniofacial structures developed earlier. In later growth, structures away from the head grow more to catch up. This is called the cephalocaudal gradient of growth, and it’s an important part of the growth pattern that you need to always keep in mind.

Question 6

What is the sample size effect?

Answer 6

Normal variation leads to a bell shaped curve in the distribution of individuals within a group. Most individuals cluster at the midpoint of the distribution and few are around the extremes. The bigger the group the more obvious the clustering near the mean.

Question 7

What does it mean if there is no bell-shaped curve?

Answer 7

The distribution is not a normal distribution and the rules that apply to normal distributions don’t apply to this.

Question 8

What is the range mean and SD?

Answer 8

Range is from smallest to largest value

Mean is arithmetic average

SD is calculated from mathematical formula describing the variability

Question 9

What do growth charts tell us?

Answer 9

Growth charts, expressed in percentiles, often are used to show how a patient compares to his or her peers in height and weight, and how that changes over time.

Lines tell us the percentiles. x-axis is time and y-axis is height or weight.

Question 10

What do percentiles of growth charts tell us?

Answer 10

Normal growth follows the percentiles consistently (a 20 percentile child may be small but if he consistently plots at 20 percentile he is healthy)

Crossing the percentiles, particularly crossing several of them, usually indicates abnormal growth and some problem. In this respect, height is a more sensitive indicator than weight.

Question 11

What does timing of growth/growth spurts tell us?

Answer 11

Boys and girls get bigger over time, of course, but differences between individuals of the same age and gender, and differences between the sexes, are most notable near adolescence. That is because sexual maturation leads to an adolescent growth spurt. This happens at a different time in girls and boys and happens at different times in individuals of the same gender. On the average, girls have their adolescent growth spurt 2 years ahead of boys. That doesn’t mean that all girls mature faster than all boys–there’s too much individual variation for that to be true.

Question 12

What does crossing the percentiles during adolescence tell us?

Answer 12

It shouldn’t be considered a problem especially if the plot for the early or late maturing person returns to normal.

Question 13

How can biological age be measured?

Answer 13

It can be measured in terms of progression towards certain developmental markers.

For dentists and orthodontists, a good way to do this is to use the stages in maturation of cervical vertebrae, which are seen in the cephalometric radiographs that are obtained for most orthodontic patients.

Question 14

What is used for calculation of biological age?

Answer 14

Many different types of maturation, not just the skeletal age calculated from vertebrae or other skeletal indicators, can be determined and quantified in biologic terms. Dentists use dental age all the time, judging the state of development of the dentition against the usual chronologic markers.

Question 15

What are the types of growth data obtained?

Answer 15

Cross-sectional study data (groups of 9 10 11 year olds)

Longitudinal study data (Following the same individuals over a long period of time)

Question 16

How can the problem of timing be avoided when measuring growth patterns?

Answer 16

The effect of plotting the individual data can be done with menarche as a base. Using biologic age in that way with cross-sectional data can make it easier to avoid distortions due to different timing in different individuals.

Question 17

How do other transformations of data besides velocity and growth curves tell us more about foetal growth?

Answer 17

Various other mathematical transformations of data can make it easier to understand what is occurring during growth. In image 1, the graph showing the increase in weight of early embryos, you can see that there is an exponential acceleration in weight with increasing time.

In image 2, the same data are plotted after a logarithmic transformation. This shows a straight line, indicating that the rate of multiplication of individual cells remains almost constant. It’s not that cells are dividing faster as the embryo gets older, it’s that increasingly there are more cells to divide.

Question 18

What are the 4 basic methods for measuring physical growth?

Answer 18

Craniometry

Anthropometry

Cephalometric radiography

3D radiography (CT)

Question 19

What is craniometry?

Answer 19

The scientific measurement of skulls, especially in relation to craniology.

Question 20

What is anthropometry?

Answer 20

Anthropometry refers to measurements on living individuals. Various landmarks on the skull were established by investigators studying skeletal material, and the soft tissue points overlying those landmarks (or other soft tissue points that can be found repeatedly) can be used to study living individuals.

Question 21

How is anthropology done in a way to avoid reliance on cross-sectional data and instead on longitudinal data?

Answer 21

Varying soft tissue thickness introduces a source of error if the goal is to measure growth of the facial skeleton, but it is highly advantageous to follow the growth of an individual directly, making the same measurement repeatedly at different times

Anthropometric measurements are still important in clinical examination of orthodontic patients. They are used now primarily to establish facial proportions–which are important in planning orthodontic treatment.

Question 22

What is cephamometric radiology?

Answer 22

The third important measurement technique is cephalometric radiology. Using x-ray pictures of the head and face provides a way to combine the advantages of crainometry and anthropometry.

It allows direct measurement of the skeleton because the soft tissue thickness can be ignored—but the soft tissues also are imaged and can be measured if desired.

Proper positioning of the subject in a head holder is necessary, so that repeated x-rays can be made with the head positioned exactly the same. This allows longitudinal study of growth (or treatment) changes in an individual.

Question 23

What are the disadvantages of using cephalometric radiology?

Answer 23

Exposure to X-rays is required

2D image instead of 3D

Some measurements are not possible and others distorted

Question 24

What are the advantages to cephalometric images?

Answer 24

Cephalometric radiographs give an excellent view of many skeletal and dental structures that aren’t accessible for anthropometric study,

These radiolographs are used routinely in dentistry to monitor growth and treatment of patients

Question 25

What are the disadvantages of using axial CT scans for imaging?

Answer 25

It is expensive

It delivers a large radiation dose

Question 26

How are CB-CT images used to measure changes over time?

Answer 26

For growth studies, images of CB-CT from before and after are superimposed.

Question 27

How is superimposition of CB-CT different to cephalometric radiographs?

Answer 27

With cephalometric radiographs, tracings based on identification of landmarks typically are used.

That doesn’t work with 3-D images, but now it is possible to superimpose on surface contours, and changes between sequential 3-D images can be discerned by color maps. This allows you to look at the amount of change at thousands of points that can be viewed from any orientation, instead of being limited to tens of points seen from one orientation in a cephalometric radiograph.

Question 28

What are the experimental methods used in the study of growth?

Answer 28

Vital staining

Autoradiography

Cephalometric superimposition on implants

Molecular biology

Question 29

What is vital staining?

Answer 29

Dyes that are incorporated into bone are injected and this allows amount of growth to be seen.

It shows both the site of growth and the rate of growth. The sites of growth are the areas where new bone is being formed, or removed by the remodeling that accompanies bone growth. The rate of growth is shown by the distance between bands of color that were deposited at known times when the dye was injected.

Question 30

What is autoradiography?

Answer 30

It is based on tissues taking their own pictures by using radioactively labelled substances.

Radioactive labels injected -> Tissue specimens prepared -> photographic film is put over the tissue and the location of these materials can be located via silver grains being activated in the film.

Question 31

How is implant radiology used to visualize changes in bone structure/size?

Answer 31

Implant radiology is based on visualizing metal pins placed in the skeleton. Perhaps you know that when bones are fractured, metal pins often are placed to hold them while they heal, and often the pins are left in place. A long time after the fracture has healed, the pin will still be visible on x-rays as a marker of the fracture site. It is possible experimentally to place small metallic implants in bones anywhere in the skeleton, including the face and jaws, as permanent markers.

Question 32

How can molecular techniques be used to analyse growth?

Answer 32

It also is possible to use the techniques of molecular biology to study growth, and this holds great promise for the near future. An example of such methods is diagrammed on this slide. Genetic information carried by plasmids can be injected into the nucleus of a mouse egg, which is then implanted into a pseudopregnant mouse.

Question 33

Summary:

Answer 33

In studies of growth and development:

Growth (increase in size) and development (increase in complexity with specialization and loss of potential) are different concepts

Growth pattern refers to predictable changes in proportions with growth

Children outside the 3rd and 97th percentiles on standard growth charts may be beyond normal variation

The timing of adolescence is a major contributor to variability in growth

Biologic ages based on physiologic events can be used to reduce variation related to timing

Important measurement techniques to know:

Craniometry

Anthropometry

Cephalometric radiology

Cone-beam CT

Remember: the timing of adolescence is a major contributor to variability in growth

Cross-sectional growth studies:

Quicker, less expensive, less precise in detecting typical timing fluctuations

Longitudinal growth studies:

slow, expensive and hard to maintain, very efficient and excellent in showing details

Experimental marker techniques to know:

Vital staining

Autoradiography

Implant superimposition

Molecular biology techniques: The way of the future in growth studies.

Question 34

What does calcification of extracellular material lead to?

Answer 34

Leads to a critical distinction between soft or non-calcified tissues and the hard calcified tissues.

Question 35

What kinds of tissues are considered “hard tissues and which are considered soft?

Answer 35

Hard tissues: Bone, teeth, and sometimes cartilages.

Soft tissues everything else including some cartilages.

Question 36

How does soft tissue grow?

Answer 36

By a combination of hypertrophy and hyperplasia. Within tissues it can occur resulting in interstitial growth. Secretion of extracellular material can also accompant interstitial growth by hyperplasia (primary) and hypertrophy (secondary)