A new study has found that people who received frequent dental x-rays in the past have an increased risk of developing meningioma - a type of brain tumor. The study was published online Tuesday in Cancer, a peer-reviewed journal of the American Cancer Society.
The study found that ionizing radiation is the primary environmental risk factor for developing meningioma, which is the most frequently diagnosed primary brain tumor in the United States. Dental x-rays are the most common artificial source of exposure to ionizing radiation for Americans.
Study researcher Elizabeth Claus of the Yale University and colleagues studied data from 1,433 patients diagnosed with meningioma between 20 and 79 years of age between May 2006 and April 2011, and compared the information to a control group of 1350 participants with similar characteristics.
They found that patients with meningioma were twice as likely to report having a specific type of dental x-ray called a bitewing exam, and that those who reported having them yearly or more frequently were 1.4 to 1.9 times as likely to develop a meningioma when compared to the control group. Bitewing exam involves a procedure in which an X-ray film encased in a T-shaped plastic sleeve is held inside the cheek while the patient bites on the stem of the T.
In addition they found there was an even greater increased risk of meningioma in patients who reported having a panorex x-ray exam, referred to in Australia as an orthopantogram. Panorex exams are taken outside the mouth to show all the teeth. Those who reported having this exam taken under the age of 10, were 4.9 times more likely to develop a meningioma compared to controls. Those who reported having the exam yearly or more frequently than once a year were nearly three times as likely to develop meningioma when compared to the control group.
To put the results in perspective, Dr. Paul Pharoah, a cancer researcher at the University of Cambridge said in a statement the results would mean an increase in lifetime risk of intracranial meningioma in the U.K. from 15 out of every 10,000 people to 22 in 10,000 people.
“Although dental X-rays are an important tool in well-selected patients, efforts to moderate exposure to ionizing radiation to the head is likely to be of benefit to patients and healthcare providers alike,” wrote the authors.
The American Dental Association put out a statement in response to the study noting that the interviews relied on participants' memories of how often they had different types of X-rays years earlier. The statement added, “The ADA's long-standing position is that dentists should order dental X-rays for patients only when necessary for diagnosis and treatment. Since 1989, the ADA has published recommendations to help dentists ensure that radiation exposure is as low as reasonably achievable.”
But Cancer Council Australia spokesman Terry Slevin said the patients' recollections were unlikely to be wholly accurate, and that those without cancer were unlikely to be as thorough in searching their memories for tests they thought might be to blame for a health condition. “The study doesn't prove causality - what it does is put forward a reasonable hypothesis that this exposure may contribute to an increased risk of this cancer,” Mr Slevin said.
Brisbane dentist Derek Lewis, a member of the Australian Dental Association's oral health committee, said digital techniques had reduced radiation doses dramatically over the past 10 years. “Two dental X-rays is the equivalent of about eight hours' of background radiation, whereas flying to London is about 12 days' of radiation,” Dr Lewis said. “It's likely that the exposure association we're seeing here is past exposure, and past exposure levels were much higher,” explained Dr. Elizabeth Claus.
“They found a small risk (from) a pair of bitewings, but not a full mouth series, which is multiple bitewings. That inconsistency is impossible to understand to me,” said Dr. Alan Lurie, president of the American Academy of Oral and Maxillofacial Radiology. Lurie also echoed Claus' caution that radiation levels from dental X-rays when some of the participants were younger was much greater than is used now. He does warn, however, patients shouldn't assume it's fine for the dentist to take X-rays. “They should ask why are (dentists) taking this image and what is the benefit to me,” he said.
Dr. Sanjay Mallya, an assistant professor the UCLA School of Dentistry in Los Angeles, said that patients should be concerned whenever they are exposed to radiation, but “it's important to emphasize that this concern should not mean that we shouldn't get X-rays at all.”
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