April 10, 2012 — Early or repeated exposure to dental x-rays appears to increase the risk for meningioma, the most commonly reported primary brain tumor in the United States, according to a study published online April 10 in Cancer.
The study reveals a statistically significant increased risk for meningioma in people who underwent bitewing or panoramic x-rays.
"The findings presented here are important, because dental x-rays remain the most common artificial source of exposure to ionizing radiation for individuals living in the United States," the researchers report.
According to lead author Elizabeth Claus, MD, PhD, professor and director of medical research at the Yale University School of Public Health in New Haven, Connecticut, and attending neurosurgeon at the Brigham and Women's Hospital in Boston, Massachusetts, "the study presents an ideal opportunity in public health to increase awareness regarding the optimal use of dental x-rays, which unlike many risk factors is modifiable."
Most Meningiomas Are Benign
Meningiomas are tumors that arise from the meninges, which are membranes that surround the brain and spinal cord, Derek Johnson, MD, a neurologist who specializes in neuro-oncology at the Mayo Clinic in Rochester, Minnesota, told Medscape Medical News. He was not involved in the study. Although technically not brain tumors, they occur inside the skull and can push inward on the brain from the outside. The vast majority (90%) are pathologically benign, he said. Some 170,000 people in the United States have been diagnosed with these tumors.
If small meningiomas are found but are not causing any symptoms, usually observation is all that's necessary. "Finding a meningioma does not necessarily mean that it must be treated," said Dr. Johnson.
But if the tumor grows over time or causes symptoms, surgery or radiation therapy, either fractionated or with techniques such as Cyberknife or Gamma Knife, can be considered, he said.
Largest Study to Date
The researchers set out to explore the relation between dental x-rays, which are the most common modifiable source of ionizing radiation, and the risk for intracranial meningioma.
The population-based case–control study compared 1433 patients with intracranial meningioma from 4 states with a control group of 1350 people with similar traits who had not been diagnosed with a meningioma.
This study is the largest of its kind to explore the effects of relatively common dental x-rays, according to the researchers. Most previous data came from studies that looked at the effects of high-dose single exposures such as atomic bombs, or a small number of high-dose exposures like radiation therapy, the researchers note.
Over a lifetime, patients with meningioma were more than twice as likely as control subjects to report having had a bitewing exam, which uses an x-ray film held in place by a tab between the teeth, the researchers found.
Regardless of age, more frequent bitewing films were associated with increased risk. People who had meningiomas were 1.4 to 1.9 times more likely than control subjects to have received bitewing exams yearly or more often.
Bitewing x-rays are relatively common. More than 92% of the population studied had undergone one.
I think this is the best and most conclusive evidence to date.
"I think this is the best and most conclusive evidence to date that low-dose repeated exposure — the kind of thing we come into contact with relatively regularly in our day-to-day life — is likely a true risk factor for this particular tumor," Dr. Johnson told Medscape Medical News.
The less common panorex exams, which offer a 2-dimensional panoramic view of all a person's teeth and surrounding bones, were associated with a notably higher risk for meningioma among people screened when young and among those who had the exams yearly or more often. People who reported undergoing such x-rays when they were younger than 10 years of age had a 4.9 increase in the risk of developing the brain tumors. However, Dr. Johnson noted that a small sample size (22 cases) led to some instability in the odds ratio, resulting in a wide confidence interval (1.8 to 13.2). Less than half (47 percent) of case and control subjects had ever undergone a panorex exam.
Another expert said that the study highlights the dangers posed by dental x-rays. "The importance of this study is that it shows that this is not a procedure with zero risk," said Keith L. Black MD, chair and professor of the Department of Neurosurgery, director of the Maxine Dunitz Neurosurgical Institute, and director of the Johnnie L. Cochran, Jr. Brain Tumor Center at Cedars-Sinai Medical Center in Los Angeles, California. "As a general rule, we need to be more concerned about x-ray exposure, particularly in the younger population," he explained.
When Possible, Avoid Fishing Expeditions
If there is no evidence of a problem, such as a cavity or the need for a root canal that might warrant further exploration, Dr. Black advises against x-ray fishing expeditions. For more than 20 years, his dentist has asked him after his twice-yearly dental cleanings whether he wants x-rays. Without fail, he declines. "If I have no complaints and they see no cavities, I don't see the point in getting the x-rays, so I refuse," he said.
Patients and parents should have conversations with their dentists about the risks and benefits of dental x-rays, he said, so they can make the most informed, intelligent decisions about when to get them. Dental x-rays should not be indiscriminately used as a yearly screening test for patients. "They should use them only when they're only critically necessary," said Dr. Black.
Cancer. Published online April 10, 2012. Abstrac
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