Radiation Studies

Radiation quantities and units  . . . . Recently, new units for dose and dose equivalent were introduced into the metric system. The new unit of dose is the gray (Gy, 1 Gy = 100 rad) and that of dose equivalent is the sievert (Sv, 1 Sv = 100 rem). These new units are coming into widespread use and will be used in this report. In dental radiology, doses are quite small and are generally expressed in millirads (1 mrad = 0.001 rad) or micrograys (1 mGy = 0.000001 Gy). For conversion, 1 mrad is equal to 10 mGy. Similarly, 1 mrem is equal to 10 mSv.

Genetic effects . . . . In 1970, the estimated genetically significant dose was 200 mSv (20 mrem) from medical diagnostic procedures. From dental procedures, it was less than 1 mSv (0.1 mrem); thus the dental contribution to the genetic radiation burden of the American population in 1970 was excluded from the calculation. From these data it can be estimated that medical radiology contributes about 20% of the genetic radiation burden of the American population., whereas dental radiology contributes less than 0.1%.

Occupational exposure  . . . .The National Council on Radiation Protection and Measurements (NCRP) currently recommends a maximum permissible dose equivalent from occupational sources of 0.05 Sv (5 rem) per year. A mean exposure of 100 mSv (10 mrem), range 50 to 600 mSv (5 to 60 mrem), in a one-month period among 231 dental personnel in 72 private dental offices has been reported. In addition, the NCRP recommends an occupational limit of 0.005 Sv (500 mrem) to the embryo-fetus during the entire term of pregnancy.

Summary and conclusions  . . . .There is at present no proof of such effects from doses commonly employed in dental practice. . . . Recent analyses suggest that the cancer risk to a patient from a dental radiographic examination is of the order of one in a million; the genetic risk is substantially less, about one in a billion. However, we currently accept risks of similar magnitude in our daily lives (Table 9). . . . It therefore appears reasonable that the information gained from a justified and properly conducted radiographic examination outweighs the risk.

Journal of the American Dental Association, Vol. 105, August 1982, pgs. 275-281

Biological effects of radiation from dental radiography  . . . . At present, there is no proof of such adverse effects from doses currently employed in dental practice. . . . "

Radiographs during pregnancy  . . . . They concluded that the recommended guidelines need not be altered for a pregnant patient. . . . Uterine doses for a full-mouth radiographic series have been shown to be less than 1 mrem. On the other hand, the uterine doses from naturally occurring background radiation during the 9 months of pregnancy can be expected to be about 75 mrem. There appears to be no rationale to preclude a properly justified dental radiographic examination because of pregnancy.

Matteson, S.R., Joseph, L.P., Bottomley, W., et., General Dentistry, July-August 1991, 264-269.

X-ray, How it works - X-ray machines pass radiation through an area and cast a shadow image on a photographic plate. The amount of radiation has decreased substantially. Necessary X-rays are generally considered safe for pregnant women, though a lead shield should be placed over the abdomen.

Young, Stephanie, Glamour, January 1996, pg. 35.

Heritable Effects - At least 1 Gray (100 rad) of low dose-rate x-radiation is required to double the mutation rate in man. This is a comforting finding as dental exposure to the gonads is in the range of one millirad.

Dental Risk Implications  . . . . Note that diagnostic radiation accounts for only about 11% of all exposure. Only about 3% of this 11%, or about 0.3% of the total exposure, results from dental radiography. Compare this to radon, for instance, which is estimated to contribute more than half the human exposure.

White, S.C., American Academy of Oral & Maxillofacial Radiology Newsletter, Vol. 17, No. 4, Autumn, 1990, pgs. 1-7.

It is easy to use the new unit. You have to remember that natural radiation background is about 3 mSv or 300 mrem per year. . . . Radiation that strikes only part of the body, such as medical x-rays, is not as hazardous as the same amount of radiation to the whole body.

Typical BERT's (Background Equivalent Radiation TIme) of ionizing radiation from medical x-rays are: a dental bitewing, about one week; a chest x-ray about ten days; a mammogram, about three months; and a barium enema x-ray study, about one year.

Cameron, J. R., American Academy of Oral & Maxillofacial Radiology Newsletter, Vol. 24, No. 3, Summer, 1997, pg. 17.

Discussion  . . . . Six typical forms of drywall construction have been tested as barriers against primary and secondary dental x-radiation. It is concluded that this widely used type of wall construction is generally effective for this purpose. . . . In general, no lead need be incorporated in the walls. . . . Thus, this investigation found that relatively inexpensive, widely used types of wall construction afforded an adequate degree of protection against dental x-radiation.

MacDonald, J.C, Reid, J.A., Univ. of Western Ontario, OOO Journal, March 1983, Vol. 55, No. 3, pgs. 319-326

Leaded Aprons: The value of leaded aprons is minimal compared to the benefits of the use of E-speed film, rectangular collimation and thyroid collars for patients under 30. The use of leaded aprons can be considered optional, except where required by law.

Pregnant Patients: Because the exposure to an embryo or fetus from dental radiography is so low compared to background radiation, dental radiographs of the pregnant patient should be made when clinically indicated.

American Academy of Oral & Maxillofacial Radiology Newsletter, Vol. 25, No. 4, Autumn 1998, pgs 6-7

There is no justification for the routine use of lead aprons for patients in dental radiography. Their use during panoramic radiography is positively discouraged. Para 103 states: "It has been argued in the past that the routine use of lead aprons for dental radiography could be justified to allay perceived patient anxiety. Their use, however, is unnecessary in view of the very low effective doses involved in properly conducted dental radiography."

Para 60 discusses radiography in pregnancy. The NRPB has recently issued a statement on diagnostic X-Rays during pregnancy and has concluded that: "the normal selection criteria for dental radiography do not need to be influenced by the possibility of a female patient being at any stage of pregnancy."

British Dental Association News, October 1994