Frequent dental X-rays are associated with an increased risk of developing the most common, noncancerous brain tumors, according to a new study, a finding that researchers say should serve as a reminder that even dental X-rays may be harmful if ordered too often.
Far from suggesting that people should skip dental X-rays, the researchers said that the new information should become part of the conversation people have with their dentists, especially since the American Dental Association’s guidelines suggest that healthy patients without cavities and free of risk factors should get bitewing X-rays once every one to three years, depending on their age.
“The broader public health message is that probably the increase in risk to a given individual, given the current dose [of radiation exposure] is low,’’ said Dr. Elizabeth Claus, a professor of public health at the Yale University School of Public Health and a neurosurgeon at Brigham and Women’s Hospital, who led the study published Tuesday in the journal Cancer.
“But you could say, gee, if this is a primary exposure in the US and we can lessen the exposure,’’ that is something worth considering, Claus said.
Researchers surveyed 1,433 patients who had the brain tumors, called meningiomas, and compared them with 1,350 others who were tumor-free, and asked them about their dental X-ray history. They found that people who had meningiomas were twice as likely as those who did not have to ever have a bitewing X-ray. Those who reported receiving such X-rays at least once per year had increased risk at all ages surveyed.
The study has many limitations because of the way it was conducted. The data cannot be used to estimate how much any single X-ray increases an individual’s risk. Researchers depended on people’s memory of their dental X-ray history, meaning that people could have over- or under-reported the X-rays they received.
The significance of the results are also difficult to interpret now, because radiation exposure from dental X-rays has decreased over the years.
Dr. Matthew Messina, consumer adviser for the American Dental Association, said that the study is valuable and that minimizing radiation exposure is always a priority, but he worried its conclusions might be given too much weight, despite limited evidence.
He said that in his private practice, when new patients are asked when they last had a dental X-ray, they often think it was much more recent than it turns out to have been, once their previous dentist is contacted. Patients who have had a brain tumor and may be primed to think dental X-rays had something to do with the tumor, may be inclined to overestimate their X-ray history even more, he said.
“While the study is something that obviously we want to take seriously, I think it needs follow-up,’’ Messina said.
“It’s showing an inclination, saying we need to look at this more,’’ including, for example, a more rigorous check of how many dental X-rays were actually taken for a given patient.
Dr. Anita Gohel, director of radiology at Boston University’s Henry M. Goldman School of Dental Medicine, said that X-rays play an important role in dental health, but that students are taught to do a detailed visual and clinical exam first and to ensure that patients are exposed to the lowest reasonable amount of radiation.
“Even though it’s a retrospective study, we have to be careful when we use dental X-rays, like any other X-rays,’’ Gohel said.
“X-rays do cause harm, we all know that, so the benefit should always outweigh the risk, and that’s what we teach dental students.’’
Dr. William Curry, a neurosurgeon at Massachusetts General Hospital who was not involved in the study, said that although meningiomas are only cancerous in 1 to 2 percent of cases, even the benign tumors can cause significant impairment and be difficult to remove.
“They’ve done a very thorough job,’’ Curry said of the study. “You don’t know how much cumulative radiation these people were exposed to. . . . But there is a known mechanism by which the radiation associated with imaging can cause tumors, and I still think it is up to the dental profession, in particular with regard to dental X-rays, to determine which patients are really benefited.’’