Answer to Question #11819 Submitted to "Ask the Experts"

I went to a dentist to see about getting a dental implant abutment and crown. I asked for a thyroid protector but the dental technologist would not let me have one. The dental technologist took a panoramic x ray before the dentist even saw me. Then, in another room, the dentist had him take an individual x ray to be able to see the bone structure better at the molar site. He was not able to position the x ray properly because my mouth is so small. I asked for a smaller film but he said there was only one size. He gave me a thyroid protector for this x ray though. The x ray did not turn out so the dentist had him take another panoramic x ray without the lead protector.

This was eight days ago, and my head—ears, eyes, and neck—are still burning up. Now, I found out online that x-ray exposures are cumulative. Will these side effects ever go away? I am afraid I am going to get tumors from these x rays after reading various websites. I am 64 years old, and I think they should have considered the cumulative effects which I did not know about. The first few days I could barely even concentrate as the amount of burning was so intense. Will I have these side effects for the rest of my life?

It is obvious that you are quite concerned about what happened at your last dental visit. First, let me confirm what your dentist likely told you about the radiation dose from panoramic radiographs: this type of imaging requires the smallest amount of radiation of any x-ray technique for the teeth and jaws. A common way of looking at x-ray amounts for various imaging techniques is to convert them to a unit called "effective dose." This allows us to compare different types of x-ray exams and also to compare them to the amount of natural background radiation we receive every day.

Before I give you the numbers for panoramic radiographs, let me mention a little bit more about background radiation since that is what is commonly used for comparison. We are all exposed to natural background radiation every day, from sources like outer space (cosmic rays) to radon to naturally occurring radioactive material in the soil. The average background dose in the United States from this natural radiation is 3.1 millisieverts per year (mSv y^-1) or about 0.8 microsievert per day (µSv d^-1). People who live at high altitudes, such as in the Rocky Mountain states, receive more than the U.S. average due to increased cosmic radiation. No health problems have been found with this amount of radiation, even in the high-altitude states.

Radiation doses for many different types of x-ray examinations have been measured and converted to effective dose for comparison. The effective dose from panoramic radiographs has been calculated to be 9–24 µSv or the equivalent of one to three days of natural background radiation. (The range in numbers is due to slight design differences in the different brands of x-ray machines). For a full-mouth series of intraoral x rays (14–20 films), the corresponding number of days of background radiation equivalent is 10–46 days, depending on whether film or digital imaging is used. A medical computed tomography (CT) scan of the head requires the equivalent of 21–177 days of background radiation, depending on the technique used. So, as you can see, the dose for panoramic radiographs is very low compared to that needed for other types of examinations.

Now, let us get back to your questions. Yes, it is "legal" to take more than one panoramic radiograph on the same visit. The reason we take x rays at all is because we need information that we can't get in any other way. In your case, the dentist needed to make sure that your dental implant had enough bone around it before he made the crown for it. The only way to know that is through x rays. I don't know for sure why two radiographs were made, but I am quite sure that they were done with different head positions (the way the technician positioned you in the machine), which would provide different information.

You expressed fear about developing cancer as a result of these x rays, particularly since you have had others in the past year. Let me assure you that the risk of developing cancer from dental x rays is very, very low—so close to zero that it is unmeasurable.

You may have read that the Health Physics Society website recommends panoramic radiographs only every two to five years. In reality, dental x rays should be taken only when there is a need for them, which will vary from person to person, depending on the condition of their mouth. For many years the American Dental Association (ADA) has published guidelines for dentists on when to take x rays, based on the individual patient’s needs. The ADA has a consumer website that you may want to visit: http://mouthhealthy.org. If you click on "A-Z topics," then "X," and then "X-rays," you can read what the ADA says about dental x rays.

Regarding the symptoms you felt in the dental office after you had the x rays (nausea and burning head, ears, eyes, and neck), I don't have a good explanation for that other than emotional distress. Nausea can occur in a condition called the acute radiation syndrome, where the person gets a very large amount of radiation all at one time to their entire body (not just the jaw). How much radiation is required to produce this symptom? 1,500,000 µSv, or about 62 thousand times more radiation than you received at your dentist visit!

I have been an oral radiologist for 40 years, taught oral radiology at the University of Michigan for most of that time, and also am a member of the Health Physics Society, having completed the graduate program in health physics. In all of that time, I have never seen a person develop the symptoms after x rays that you describe. I am not saying that they are not real feelings, but I don't think they are a result of the radiation you received. Fear and emotional distress are very powerful, and they can make us feel terrible.

I hope this information is helpful to you in reducing your fear and anxiety. I want to repeat that the amount of radiation you received was indeed very small.

Radiation dose information provided in this response is from the most widely used textbook of dental radiology used in dental schools all over the world: White and Pharoah 2014.

Sharon L. Brooks, DDS, MS

Reference
White SC and Pharoah MJ. Oral radiology: Principles and interpretation, 7th ed. St. Louis, MO: Elsevier; 2014.