Science-- there's something for everyone

Tuesday, May 1, 2012

Dental x-rays and cancer

The most common type of ionizing radiation most people receive is in the form of dental x-rays. The most common type of brain cancer is meningioma. Elizabeth Claus of Yale and her colleagues from four other schools wondered if the two were related. Their preliminary tests show that they may be, but it’s nothing to panic over.

It’s well known that ionizing radiation can cause cancer.  However, previous associations have been made for people who received very high levels of radiation, ironically for the treatment of other cancers. Could dental x-rays cause the same problems?

The researchers compared the records and recollections of 1433 people who had been diagnosed with intracranial meningioma with those of 1350 controls. Each person was asked whether they’d ever had dental x-rays, and if so, what kind and how often. Sure enough the people who had had dental x-rays, particularly those who’d had them as kids, were significantly more likely to have meningiomas later in life.

I have three comments about this study. First and foremost, the x-rays that dentists use today are not your grandfather’s x-rays. Radiation is measured in rems or sieverts (one sievert equals 100 rems). A typical person receives about 360 mrems (thousandths of a rem) per year just going about his day. In the 60’s, when the majority of the participants were kids, dental x-rays used at least thirty times more radiation than today’s digital x-rays. Nowadays, a person is likely to receive fewer than 6 mrem from a visit to the dentist.

Second, retrospective studies that rely heavily on people’s memories can be problematic. In this case, although single x-rays (known as ‘bite-wings’) correlated with a significant increase in brain cancer, full mouth x-rays, which are essentially a group of four or more bite-wings, did not. Does this demonstrate a problem with the data collection or with the conclusions?

Finally, even if there is a direct link between dental x-rays and meningioma, this does not mean that people should stop getting dental x-rays. Based on the results, about seven more people out of every 10,000 could be getting cancer from their x-rays.  Meanwhile, detecting cavities and other oral problems early can have great benefits for one’s overall health.

Personally, I think I’ll be a bit more cautious about accepting dental x-rays for myself or for my family, but I won’t forego them entirely unless much more evidence comes out.