Answer to Question #14523 Submitted to "Ask the Experts"

I am extremely nervous regarding dental x rays. In the last year, I have had several dental issues that required x rays. Now I am having more dental problems and the dentist suggested I have a (cone-beam computed tomography [CBCT]) scan. When doing conventional x rays, the dentist always informs me that the radiation exposure is minimal. Keeping in mind my cancer history, should the radiation exposure of a CBCT scan be something I should be concerned about? 

I understand that you are concerned about having a CBCT. You are correct that conventional dental x rays are extremely low radiation exposure. A CBCT is a low dose scan that will allow your dentist to evaluate the anatomy of the jaws in all three planes and can be a useful tool for many dental problems. It is the recommended examination to determine anatomical relationships as stated by the position statement of American Academy of Oral and Maxillofacial Radiology, if an implant is going to be placed or if there are any problems with an implant that has already been placed.  

The amount of radiation received from a cone beam CT of the jaws will vary from approximately 18–200 µSv depending on the size of the field of view, resolution of the images, size of the patient, location of the region of interest as well as the manufacturer settings. However, on average an 8 cm × 8 cm field of view cone beam CT is actually less dose than a conventional film based full mouth set of x rays and slightly more than a full mouth set of digital x rays. Compared to the effective dose for a panoramic radiograph (conservatively estimated at approximately 14.2 µSv), a cone-beam CT is similar to having approximately nine panoramic radiographs depending on the factors stated above. We can assume that an average radiation dose for a cone beam CT of the jaws taken for implant purposes is approximately 130 µSv. We can also compare the dose of ionizing radiation from a cone beam CT to ubiquitous background radiation. That is the amount of radiation that a person receives just being on the earth every day. In the United States we receive approximately 8.5 µSv daily. The average 8 cm × 8 cm field of view CBCT is equivalent to being alive on the earth for approximately 15 days. In comparison, a medical CT of the head is approximately 860 µSv which equates to approximately 105 days of being alive on the earth.

The amount of radiation received for a cone-beam CT is minimal in comparison to what we receive being alive on the earth. However, we always want to be careful with any amount of radiation and will use the principles of As Low As Reasonably Achievable (ALARA) as well as patient selection criteria when deciding what dental images should be taken. A cone beam CT can be a very useful tool in planning your dental treatment and your dentist will only use this tool when the benefits of the examination outweigh any of the minimal risks. Considering your history of thyroid cancer with subsequent treatment, you may actually be at increased risk for dental caries and apical lesions. Therefore, a cone beam CT may be a very beneficial low-dose diagnostic examination and will help your dentist to more accurately and confidently diagnose what is currently occurring with your dental problems.

Heidi Kohltfarber, DDS, MS, PhD