Methods of studying growth555555555.pptx

prothodontics

1. Methods of studying growth

2. Measurement Approaches Craniometry Anthropometry Cephalometric Radiology Three-Dimensional Imaging

3. Experimental Approaches Vital Staining Implant Radiography Radio isotopes Autoradiography

4. Methods Of Gathering Data CROSS SECTIONAL METHOD Groups of various ages are examined at single time LONGITUDNAL METHOD Measurements are made of the same person or group at regular interval over a prolonged period Semi longitudinal study This type of study is a compromise between the cross sectional and pure longitudinal studies

5. Craniometry based on measurements of skulls found among human skeletal remains . Craniometry has the advantage that precise measurements can be made on dry skulls. T he important disadvantage for growth studies that all these growth data must be crosssectional . Cross-sectional means that although different ages are represented in the population, the same individual can be measured at only one point in time.

6. Anthropometry M easure skeletal dimensions on living individuals. In this technique various landmarks established in studies of dry skulls are measured in living individuals simply by using soft tissue points overlying these bony landmarks. This measurement can be made on either a dried skull or a living individual, but results would be different because of the soft tissue thickness overlying both landmarks . Although the soft tissue introduces variation, anthropometry does make it possible to follow the growth of an individual directly, making the same measurements repeatedly at different times. This produces longitudinal data: repeated measures of the same individual. In recent years,

7. Cephalometric Radiology The technique depends on precisely orienting the head before making a radiograph, with equally precise control of magnification. This approach can combine the advantages of craniometry and anthropometry. It allows a direct measurement of bony skeletal dimensions, since the bone can be seen through the soft tissue covering in a radiograph, but it also allows the same individual to be followed over time . The disadvantage of a standard cephalometric radiograph is that it produces a two-dimensional (2-D) representation of a threedimensional (3-D) structure, and so, even with precise head positioning, not all measurements are possible.

8. Three-Dimensional Imaging Computed axial tomography (CAT or more commonly, CT) allows 3-D reconstructions of the cranium and face, and this method has been applied for several years to plan surgical treatment for patients with facial deformities. Recently, cone beam rather than axial CT has been applied to facial scans. This significantly reduces both the radiation dose and cost . Cone beam CT (CBCT) allows scans of patients with radiation exposure that is much closer to the dose from cephalograms . Superimposition of 3-D images is much more difficult than the superimpositions used with 2-D cephalometric radiographs, but methods developed recently are overcoming this difficulty . Magnetic resonance imaging (MRI) also provides 3-D images that can be useful in studies of growth, with the advantage that there is no radiation exposure with this technique. This method already has been applied to analysis of the growth changes produced by functional appliances .

9. Vital Staining This technique in which dyes that stain mineralizing tissues (or occasionally, soft tissues) are injected into an animal . These dyes remain in the bones and teeth and can be detected later after sacrifice of the animal. This method was originated by John Hunter in the eighteenth century.

10. He discovered that the active agent was a dye called alizarin, which still is used for vital staining studies . Alizarin reacts strongly with calcium at sites where bone calcification is occurring . Since these are the sites of active skeletal growth, the dye marks the locations at which active growth was occurring when it was injected . Bone remodels rapidly, and areas from which bone is being removed also can be identified by the fact that vital stained material has been removed from these locations

11. Implant Radiography In this technique, inert metal pins are placed in bones anywhere in the skeleton, including the face and jaws. These metal pins are well tolerated by the skeleton, become permanently incorporated into the bone without causing any problems, and are easily visualized on a cephalogram . This method of study was developed by Professor Arne Björk .

12. Radio isotopes We use almost any radioactively labeled metabolite that becomes incorporated into the tissues as a sort of vital stain . The location is detected by the weak radioactivity given off at the site where the material was incorporated . The gamma-emitting isotope [ Tc ] can be used to detect areas of rapid bone growth in humans, but these images are more useful in diagnosis of localized growth problems than for studies of growth patterns .

13. Autoradiography T echnique, in which a film emulsion is placed over a thin section of tissue containing the radioactive isotope and then is exposed in the dark by the radiation. After the film is developed, the location of the radiation that indicates where growth is occurring can be observed by looking at the tissue section through the film.

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