Answer to Question #11072 Submitted to "Ask the Experts"

My six-year-old daughter recently got her first set of bitewing x rays at our family dentist. I requested they cover her thyroid and use the apron shield. I did not think about asking if their machines had lower settings for children. I believe they are using the same settings for everyone. They have an older machine and I think they use D speed film. I am concerned that she got a double dose for these bitewing x rays. There are not many choices in my area for dentists who have digital x ray machines. I think lower settings for children may not be used as often as they should. Should I be overly concerned about this?

As a mother of two little girls I certainly understand your concern with radiation doses. We always want to be careful with the amount of radiation that any person receives especially a child. 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. The interval for receiving radiographs such as bitewings 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.

Most dentists in the United States have switched from D speed film to faster speed films (F speed) or digital radiographs. There are two types of digital radiographs. Photostimulable phosphor plates (PSP) work similar to film and are termed "indirect digital" radiographs. They are used with approximately the same radiation settings as F speed film and look very similar to film. The second type of digital radiographs is called "direct digital" and they contain a sensor that is wired to a computer and decrease the radiation dosage considerably. As a parent, I would ask my dental provider whether they are using film-based radiographs or PSP plates. If film is being used, which one are they using and are the exposure settings adjusted for children? There is a difference between the exposure settings for D speed film verses F speed films and exposure settings are typically decreased for pediatric patients.

It is also important to note that we do 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. Below is a table that shows bitewing radiographic examinations performed with D speed film and F speed film/indirect digital (PSP) plates. 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. This can be compared to the number of other common radiographs children might receive such as panoramic radiographs that equate to the same radiation level and it can be equated 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. In addition, the type of "cone" or end of the x-ray head that is used can affect the amount of radiation. A round collimator is usually encountered in private practice but results in a higher radiation exposure to the patient. Most dental schools in the United States have now adopted a rectangular collimator and are hoping that as new dentists graduate they will adopt the new equipment and help to further decrease the dose to patients.

Depending on the number of bitewings that were taken (usually two for pediatrics) using D speed film versus the faster or digital films will have a minimal overall increase in radiation dose and you should not be overly concerned. However, you may ask your dentist to change to faster speed film such as F speed if you are concerned because it is a very simple change for a dental office to make. I would imagine that your dentist values your family’s business and time and would be willing to change if there is a concern. If your dentist is not amenable to changing then I would take the time to look for a dentist that is more current in their use of faster speed films because it may indicate that your dentist is not willing to be current in other areas of dentistry as well.

Heidi Kohltfarber, DDS, MS, Dip. ABOMR
Assistant Professor

References

• Ludlow John B, Davies-Ludlow Laura E, White, Stuart C. Patient risk related to common dental radiographic examinations. J Am Dent Assoc 139 1237-1243; 2008.
• National Council on Radiation Protection and Measurements. Radiation protection in dentistry: recommendations of the National Council on Radiation Protection and Measurements. Bethesda, Md.: National Council on Radiation Protection and Measurements; 2003:7.