The thyroid gland is sensitive to radiation, and radiation exposure is a known cause of thyroid cancer. But dental x-rays have long been overlooked as a source of radiation, given the low dose of the radiation used.
Repeated exposure, however, now appears to be correlated to an increased risk of thyroid cancer, and according to the researchers, their findings correlate to previous research that has found an increased risk of thyroid cancer in dentists, dental assistants, and x-ray workers.
The researchers found that study subjects who had up to four dental X-rays had more than double the risk of developing thyroid cancer than those who had never had a dental x-ray. Those who had between five and nine X-rays had a risk more than four times normal. And the greatest risk was for those with ten or more X-rays, whose risk was more than five times that of someone who had not received dental x-rays.
Lead investigator Dr. Anjum Memon has said that the implications of the findings are especially important, given the increased rate of thyroid cancer in the past 30 years. In the US, for example, thyroid cancer is the fastest growing form of cancer, and in the United Kingdom, the thyroid cancer rate has doubled from 1.4 per 100,000 in 1975, to 2.9 per 100,000 in 2006.
The researchers are cautioning, however, that the topic requires further research and study, especially to get a better estimate of the radiation doses and number of exposures that are more associated with an increased risk.
What Can You Do?
Given this new information, what should you do to help protect yourself against thyroid cancer?
According to the study author Dr. Memon: "Our study highlights the concern that, like chest or other upper body X-rays, dental X-rays should be prescribed when the patient has a specific clinical need, and not as part of routine check-up or when registering with a dentist. 'So, one of the first things you can do is to make sure that you get dental x-rays only when your dentist has a specific need for them, and not just as a routine part of treatment, i.e., routine annual x-rays, or a routine dental x-ray with every checkup.
Second, and this is a recommendation that I've been making for years here at the site and in my books: Ask the dentist to protect you with a lead thyroid collar when doing any x-rays. This is a recommendation that you'll also hear from About.com's guide to Dentistry, Shawn Watson, who says: "Before you have x-rays taken at your dental office, make sure the protective lead vest, that is placed over your body prior to taking an x-ray, has a thyroid collar." (My own dentist didn't even have a thyroid collar for the longest time. He used to look at me a bit strangely when I would ask that he protect my thyroid for dental x-rays. I would end up pulling the lead apron up so that it would go right up to my chin. Now he has an actual thyroid shield on his lead apron, thankfully!)
Third, if you have young children, minimize their exposure to any unnecessary dental x-rays, and insist that their dentists and orthodontists also use a thyroid collar. Children are especially susceptible to thyroid-damaging radiation, so you'll want to ensure they are not subjected to routine or unneeded dental x-rays. And for children, any essential x-rays should only be conducted with use of the appropriate lead thyroid collar.
Source: Memon, Anjum et. al. "Dental x-rays and the risk of thyroid cancer: A case-control study," Acta Oncologica, May 2010, Vol. 49, No. 4, Pages 447-453. Abstract/Summary.