The Use of X-Rays in Dentistry

10 October 2016

Dentistry is increasingly becoming a major part of people lives in today’s society, being taken for granted and often little thought about. As technologies advance treatment becomes cheaper, quicker, and the outcome becomes more aesthetically pleasing and longer lasting. As braces, dentures, crowns, procedures and techniques change and improve at an alarming rate, one aspect has remained the same for a longer period of time. This is the use of X-Rays.

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X-Rays have been used in dentistry since the mid 1900’s, and continue to be used in the same way today. They are an effective way of finding and identifying various oral problems, allowing for early prognosis and prevention of more serious issues. How is an x-ray produced? Diagram showing a Dental x-ray tube. In a dental (and most other uses of x-rays including all medical uses) x-ray tube, x-rays are formed as electrons from a hot wire filament are accelerated onto a target anode. A high-voltage unit is used to set the anode at a large positive potential compared to the negatively charged filament.

The electrons are pulled onto the anode at very high speeds and are suddenly decelerated on impact. As this impact occurs, some of the kinetic energy is converted into electromagnetic energy, as x-rays. This means that the anode therefore emits x-rays as a result of being smashed with high-energy electrons. The x-rays spread out from the focal spot, through the tube window and onto the region to be examined. How is an image formed? X-ray films that are used in dental radiography consist on an emulsion/gelatine mix containing chemicals that are sensitive to x-ray radiation.

This is a silver halide – either bromide or chloride. The emulsion/gelatine mix and their suspension is set onto a flexible, transparent tinted blue base. Emulsion is used in all types of analogue photography, but the type used in x-ray photography is of a different kind to that used in light photography. The emulsion is usually coated on both sides of the base in layers around 0. 1mm thick. As both sides of the base are coated, there is twice the amount of radiation sensitive silver halide, and so the speed at which an image is produced is increased significantly.

Another way to increase the speed of producing an image would be to just have one side with a larger thickness of emulsion. This however would slow down the developing, fixing and drying stage, meaning taking x-rays would take an unreasonable amount of time. Some x-rays requiring more detail use film with emulsion on one side only. When x-rays, gamma rays, or light strike the grains of the sensitive silver halide in the emulsion, some of the halide (Br- or Cl-) ions are released and captured by the silver (Ag+)ions.

This chemical change is of such a small nature that it cannot be detected by ordinary physical methods and is called a “latent (meaning hidden) image. ” However, the exposed grains are now more sensitive to the reduction process which happens during development of the film. When exposed to a chemical solution (the ‘developer’), and the reaction results in the formation of black, metallic silver. It is this silver, suspended in the emulsion-gelatine on both sides of the base that creates an image. Seeing things with X-Rays

Different materials have different properties, including x-ray absorption ability. This is exactly the same with body parts, especially teeth. Radiation passes through skin the easiest, followed by the guns and soft tissue. These parts show up as the very darkest areas on an x-ray. Harder tissues absorb and black more radiation from hitting the film and so show up as much lighter areas. Metal implants, fillings and crowns (most artificial features) show up as the brightest white. The different depths of materials is also shown, nerve endings and dentine contours being visible on most developed films.

This image shows that a root canal procedure has been successfully completed, meaning less time and money is wasted fixing procedures that have failed. Also visible is an amalgam filling (Brightest white) Measuring Radiation – The Sievert The sievert (Sv) is the International System of Units (SI) derived unit of equivalent radiation dose, effective dose, and committed dose. Quantities that are measured in sieverts are designed to represent the stochastic biological effects of ionizing radiation.

The sievert should not be used to express the unmodified absorbed dose of radiation energy, which is a clear physical quantity measured in Grays. To enable consideration of biological effects, further calculations must be performed to convert absorbed dose into effective dose, the details of which depend on the biological context. This can be far more complicated than just multiplying by a weighting factor. The sievert is a fundamental part in radiation dosimetry, and is named after Rolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dosage measurement and research into the biological effects of radiation.

One sievert equals 100 rem, an older unit of measurement still used in many areas and by older generations of practitioners. One sievert carries with it a 5. 5% chance of eventually developing cancer. Doses greater than one sievert received over a short time period are likely to cause radiation poisoning, possibly leading to death within weeks. This is a major risk considered in dental use as many doses of radiation could be received during a day in surgery.

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