Are dental X-rays dangerous?
Some people do not want diagnostic x-rays because they have heard that the radiation is dangerous. In fact, they pose very little danger. There are currently two units used to measure the exposure of biological organisms to radiation.
These units are measures of equivalent dose. Equivalent dose units are used to compare radiation doses on different body parts because radiation does not affect different parts in the same way. Equivalent dosing units allow for a more meaningful comparison between radiation sources that expose the entire body (such as natural background radiation) and those that only expose a portion of the body (such as dental vs. medical radiographs).
The first, oldest and still probably the most frequently used unit of equivalent dose in the US is called a rem. A second unit, used outside of the US is the sievert. 1 sievert = 100 rems. A rem is a large unit, (And a sievert is an even larger unit), so exposure to medical radiation is generally measured in millirems (mREM) and millisieverts (mSV). Other units you may hear about are measures of radiation called rads and grays. These are units of absorbed dose, and are generally applied to non biological bodies.
The average dental x-ray delivers about 1 mREM per exposure if the dentist is using intraoral film. The dose is only about .30 mREM if the dentist has made the transition to digital intraoral radiographs. Thus a full mouth series of dental x rays (18 intraoral films) delivers about 18 mREM. If the dentist is using digital radiographs using a digital sensor instead of film, the total dose to the patient is only about 6 mREM. (Note: These figures are based on the use of E-speed film which requires the most radiation to expose, but delivers the highest resolution x-ray.) A panorex film delivers about 2 mREM. By comparison, the average person in the US is exposed to about 360 mREM per year just from naturally occurring background sources. Background radiation comes from outer space, the earth, natural materials (including natural foods), and even other people. By this measure, it would take approximately 20 full series of dental radiographs if taken on film, or 60 full series if taken with a digital sensor to equal the background radiation that the average citizen is exposed to on a yearly basis. Note that most dentists take a new full series on adult patients every three to five years on average, depending on the overall oral health of the patient.
Cooking with natural gas exposes us to about an additional 10 mREM per year because of the naturally occurring radon gas the cooking gas contains. Living in a brick building adds an additional 10 mREM per year over and above the radiation you would receive from living in a wooden structure. 1,300 mRem per year for the average cigarette smoker! Simply sleeping next to another person exposes each bed partner to an extra 2 mREM per year. Yes, radiation is everywhere. Our bodies and the world around us are radioactive. But that is no cause for alarm. These very small but detectable levels of radioactivity are natural. We are exposed to a constant stream of radiation from the sun and outer space. Radioactivity is in the ground, the air, the buildings we live in, the food we eat, the water we drink, and the products we use. The average person in the United States receives a dose of about 620 millirem per year from these natural sources of radioactivity as well as from typical medical radiation.
Is a radiation dose of 620 millirem in a year harmful?
No. No effects have ever been observed at doses below 5,000 millirem delivered over a one year period. In fact, effects seen when humans are exposed to 100,000 millirem over a short time period are temporary and reversible. It takes a short-term dose of well over 500,000 millirem to cause a fatality.
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