April 10, 2012 -- Frequent dental X-rays, particularly in childhood, may be linked to an increased risk of the most common brain tumor in adulthood, say researchers who suggest minimizing the use of X-rays, especially among people without symptoms of tooth or gum problems.
Dr. Elizabeth B. Claus, an epidemiologist at the Yale School of Medicine in New Haven, Conn., and at Brigham and Women's Hospital in Boston, led the new study suggesting an association between mouth X-rays and tumors called meningiomas. The tumors, which take their name because they arise in the meninges, the membrane surrounding the brain and spinal cord, account for about a third of brain tumors detected in the United States. Although they're most often benign and slow-growing, they can cause disability by exerting pressure on the brain.
Having once-yearly or more frequent bitewing X-rays, which expose a small piece of film placed between the teeth to a beam of radiation, raised the risk for meningiomas 1.4 to 1.9 times, Claus and her colleagues found. A panoramic X-ray that sweeps around the head to grab a view of all the teeth -- often to assess the need for braces -- nearly quintupled the risk of developing a meningioma if performed before a child's 10th birthday, the team reported.
After reviewing the new research, the American Dental Association issued a statement reiterating its longstanding position that dentists should order dental X-rays "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," the ADA said in a statement, released to coincide with online publication today of the new study in Cancer, the journal of the American Cancer Society.
The ADA currently recommends X-rays every 1-2 years for healthy children and every 2-3 years for healthy adults.
Claus and her research colleagues reviewed histories of dental X-rays among 1,433 patients diagnosed with meningiomas between the ages of 20 and 79 in 2006-2011 and compared them with dental X-ray histories of healthy subjects matched for age, gender and geography. All were asked to recall dental X-rays they'd ever received.
Reaction to the study was mixed among doctors and dentists contacted by ABC News.
Dentists long have relied upon X-rays to look beyond the surface of teeth and gums for signs of cavities, infections or to visualize bones and ligaments affecting the bite. However, X-ray doses in decades past were several times higher than doses used in today's digital devices, the researchers, the ADA and outside experts agreed.
"The current study is well-done and confirms that even in the 'modern era' radiation exposure from repeated dental X-rays conveys an increased risk of these tumors," said Dr. David Schiff, co-director of the University of Virginia Neuro-Oncology Center, told ABC News.
The risk of meningioma is only 3 cases for every 100,000 people, "low enough that you can miss it without a good scientific study," said Dr. Keith L. Black, chairman of neurosurgery at Cedars-Sinai Medical Center in Los Angeles, who said there's need for a bigger, well-designed study.
X-rays employ ionizing radiation, the potentially DNA-damaging radiation that poses the greatest environmental risk for developing a meningioma. Dentists like to reassure patients that X-rays expose them to very low doses, well below naturally occurring radiation they get from the atmosphere and radioactive elements in soil.
Ask Your Dentist About Need for Mouth X-Rays
Although the study authors suggested their findings might prompt a re-examination of current recommendations, Dr. Alan G. Lurie, president of the American Academy of Oral and Maxillofacial Radiology said the new paper "does not do one iota to change the need to follow the As Low As Reasonably Achievable (ALARA) principle."
"No matter how low the dose gets, it's more than zero," Lurie said, "so you need to have a good reason" for the X-ray, he said. Patients should ask their dentists: "What is it going to tell you that will help you decide how to treat me?"
The study had two principal weaknesses, beginning with people's notoriously unreliable recall for past events, in this case past X-rays, and the lack of data on what doses of radiation they received. "You would want to know the radiation dose to the part of the brain where the meningioma occurred," said Dr. Henry D. Royal, a nuclear medicine specialist at the Mallinckrodt Institute of Radiology in St. Louis, who said that dose "should be trivial." He pronounced the paper flawed.
In his 2009 book, "Brain Surgeon: A Doctor's Inspiring Encounters with Mortality and Miracles," Black expressed his concern about frequent X-rays among youngsters undergoing orthodontia because they're "aimed not just at the jaw, but at the lower brain." An advocate for minimizing the use of X-rays in dentistry, Black said he routinely refuses dental X-rays. "I haven't had a dental X-ray in 20 years."
Although children's developing teeth are more prone to decay than those of adults, sometimes requiring more X-rays, their bodies also are more vulnerable to the effects of radiation.
Dr. Robert J. Emery, executive director for environmental health and safety at the University of Texas Health Science Center in Houston, suggested patients ask their dentists if the X-rays are "absolutely necessary," what radiation doses will be delivered, and if they use lead aprons and collars to shield organs vulnerable to radiation's effects. He also recommends that when patients first see a new dentist, they bring along copies of previous X-rays.
Dr. Paul Casamassimo, chair of pediatric dentistry at Ohio State's College of Dentistry, was even more emphatic about questioning dental X-rays: "My advice would be to challenge your dentist on why radiographs are needed in any given situation, particularly when a child is involved."
ABC News Medical Unit's Dr. Jessica Noonan contributed to this report.