Answer to Question #10700 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Dental

The following question was answered by an expert in the appropriate field:

Q

About five years ago, I had a barium test done. Three years ago I had full-mouth x rays done at my dental school. Recently I had eight bitewings, one periapical, panoramic, and another full-mouth x ray done, and there is a possibility that I need dental work done that would require additional x rays to be taken.

I am concerned that I will get cancer someday from the excessive radiation. The first set of x rays was not digital. I recently learned that digital x rays have 90 percent less radiation than the regular x rays. I am just worried about getting future dental work done and what the future might hold with my health from the radiation.

Is the dental radiation that I've received much less than active celebrities receive when constantly traveling in planes?

A


I understand that you are concerned about the amount of radiation you are receiving, particularly from dental radiographs. Your comments lead me to believe that you are receiving your dental work at a dental school. Most dental schools use photostimulable phosphor plates (PSP—known as indirect digital), which have a similar radiation dosage to regular fast-speed (F-speed) film. In addition, most schools use rectangular collimators, which will significantly decrease the amount of radiation that you are exposed to. On average, a direct digital sensor will decrease the radiation dosage by 90 percent, but due to the expense of the direct digital, they are not usually used in the predoctoral student clinics.

We encounter radiation every day just by being alive on this earth. This is known as background radiation and is caused by terrestrial, cosmic, and naturally occurring radon. We receive approximately 3,000 µSv of ubiquitous background radiation a year. This equates to approximately 8.2 µSv per day. The amount of ionizing radiation used in dentistry is considered a low dose. It is difficult to estimate cancer risks from low-level exposures due to statistical limitations; therefore, mathematical risk models are used. The most conservative mathematical risk model used today is the linear no-threshold dose-response model, which implies that there is no threshold and the risk is proportional to the dose. The current model suggests that the radiation dose may accumulate over time. It is not clear what triggers the cancer to occur or when it may be triggered. We do know that radiation is a weak carcinogen. However, we want to be careful with any amount of radiation and will use the principles of ALARA (as low as reasonably achievable) as well as patient selection criteria when deciding what dental images should be taken. Not every patient needs a full-mouth series every three years, as was once thought. The interval for receiving radiographs is now dependent on the patient's caries risk assessment (performed by your dentist) as well as the task that the images will be used for. There must be a justification and a benefit for taking each image. Below is a table that shows the radiographic examinations that you have received over the years. The effective dose in µSv takes into account the sensitivity of the tissues to ionizing radiation, as well as the volume of the tissue that is imaged. It can give a broad indication of the level of detriment to health from radiation exposure because it allows the risk to the whole body to be expressed. We can compare this to fatal cancer risks per million exams and equate it to the amount of radiation that a person is exposed to on a daily basis to try to help one understand the effects of the ionizing radiation that a person has received.

Exam Effective Dose+ in µSv Fatal Cancer Risk per Million Exams Per Capita Background*
Barium Swallow (24 Images, 106 Second Fluoroscopy)++1 1,5001 772 183 days
FMX (PSP or F-Speed Film—Rectangular Collimation)3 35 2 4.3 days
Single PA or Bitewing (PSP or F-Speed Film—Rectangular Collimation)3 2 0.1 6 hours
Four Bitewings (PSP or F-Speed Film—Rectangular Collimation) 5 0.3 17 hours
Panoramic—Indirect Digital3 14.2 0.8 1.7 days

*Based on a naturally occurring U.S. background radiation of 3,000 µSv per year (8.2 µSv per day). Source: National Council on Radiation Protection and Measurements.4
+Effective doses listed are an average
++Assuming the "barium test" is a barium swallow
FMX: Full-mouth radiographs
PSP: Photostimulable phosphor
BW: Bitewing
PA: Periapical
1Wall BF, Hart D. Revised radiation doses for typical x-ray examinations. The British Journal of Radiology 70:437–439; 1997. (5,000 patient dose measurements from 375 hospitals). Available at http://bjr.birjournals.org/content/70/833/437.full.pdf.
2Available at http://www.hpa.org.uk/Topics/Radiation/UnderstandingRadiation/UnderstandingRadiationTopics/MedicalRadiation/medic_TedEquivalent/.
3Ludlow JB, Davies-Ludlow LE, White SC. Patient risk related to common dental radiographic examinations. J Am Dent Assoc 139:1237–1243; 2008.
4National Council on Radiation Protection and Measurements. Radiation protection in dentistry: Recommendations of the National Council on Radiation Protection and Measurements. Bethesda: NCRP; NCRP Report No. 145; 2003.

 
Based on the table above, the additional risk from the radiation that you have received is minimal in comparison to the barium swallow that you received five years ago. There may be greater health risks associated from not receiving the necessary dental treatment that you require than to receive it with a few additional dental films.

Heidi Kohltfarber, DDS, MS, Dip. ABOMR

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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