Dental x-ray

Dental x-rays provide valuable information on the health of teeth which cannot be obtained by any other medical imaging modaUty. Dental x-ray procedures use a piece of film placed in the mouth between the tongue and the teeth. A 60 to 70 keV source of x-rays, located outside the mouth, is directed at the film. Metal fillings attenuate x-rays striking the film and therefore appear white in a projection image. Tooth decay appears dark as it attenuates x-rays less than normal tooth enamel. 

Arc-melted titanium has excellent fluidity and lends itself readily to the creation of thin margins. Spmes must be carefully placed and abundant venting provided, however, to avoid holes and porosity ia the casting. The detection of defects by radiography is faciUtated by the low density of titanium, and conventional dental x-ray units may be used ia many cases. 

Notice from this equation that energy is inversely related to wavelength. This explains why you put on sunscreen to protect yourself from UV solar radiation (<400 nm) and a lead apron when dental x-rays (<10 nm) are being taken. Conversely, IR (>700 nm) and micro-wave photons (>80,000 nm) are of relatively low energy (but don t try walking on hot coals). 

A university student recently had a busy day. Each of the student s activities on that day (reading, having a dental x-ray, making popcorn in a microwave oven, and getting a suntan) involved radiation from a different part of the electromagnetic spectrum. Complete the following table and match each type of radiation to the appropriate event ... 

Medical and dental diagnostics X rays - 20 mrem per visit Gastrointestinal X rays = 200 mrem per visit Dental X rays = 10 mrem per visit Radiation therapy (ask your radiologist)... 

One key difference between this application area and the previous two is that the image is usually a representation of a real object. It might be a LANDSAT photograph or a dental x-ray that needs to be enhanced. The problem that is dealt with here is not necessarily the display of the image - though that factor is here - but rather the use of graphics to extract more information from the data. 

Dental x-ray images contain more information than might be apparent to the human eye. The loss of detail is due to the low contrast level. After digitizing the image with a sensitive densitometer, the intensities can be rescaled and displayed with greater detail than we would have seen in the original image. 

The x-ray technique for crystals, however, is not the same as that of a medical or dental x-ray. In the case of a medical or dental x-ray, the x-rays are allowed to pass through the body and the images are of the shadow cast by the dense tissue—bones or teeth—that the x-rays could not penetrate. X-ray studies of crystals (called x-ray crystallography) look at reflected x-rays, rather than transmitted x-rays, and analyze the patterns in the reflected rays. 

A heavy lead-lined vest absorbs errant radiation from a dental X-ray machine, limiting exposure to the rest of the body. Dentists use dental X rays as a diagnostic tool for determining the health of teeth and gums. 

Medical and dental X rays present only a slight risk due to radiation and are of great benefit in diagnosis. ... 

People receive some radiation exposure each day from the sun, radioactive elements in the soil and rocks, household appliances like television sets and microwave ovens, and medical and dental x-rays. 

The effects of short-term exposure to radiation appear in TABLE 21.9. An exposure of 600 rem is fatal to most humans. To put this number in perspective, a typical dental X-ray entails an exposure of about 0.5 mrem. The average exposure for a person in 1 year due to all natural sources of ionizing radiation (called background radiation) is about 360 mrem (V FIGURE 21.25). 

A colour-enhanced dental X-ray showing silver/mercury amalgam fillings (yellow). 

A dental X ray typically involves what dose of radiation ... 

Figure 94. Exchange of lake nutrients studied with (a) Concentrations of in surface water and deep waters of a lake in which complete mixing occurred. Time is measured from the deposition of at the surface. The ordinate is logarithmic, (b) Autoradiograph of a frog taken from a lake, 40 days after addition of P. The concentration of tracer in the skeleton is evident. Exposure 15 days, on dental X-ray plate. From Hayes and Coffin (1951).

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