People who received frequent dental X-rays in the past, especially "bitewing" exams, more than double their odds of developing the most common type of brain tumor, says the results of a new study published in Cancer, a journal of the American Cancer Society.

Ionizing radiation is the main environmental risk for developing meningioma, the most commonly diagnosed form of brain tumor in the United States, and dental X-rays are the most common artificial source of exposure for Americans.

Dr. Elizabeth Claus of the Yale University School of Medicine in New Haven and Brigham and Women's Hospital in Boston, studied information on 1,433 patients ages 20 to 79 years old who were diagnosed with meningioma. They also studied a group of 1,350 people who didn't have the disease.

Over a lifetime, patients who developed meningioma were more than twice as likely to have had a bitewing exam. (Bitewing X-rays show the upper and lower back teeth in a single view. The X-ray film is held in place by a little tab of plastic or paper.) Those who had the exams on a yearly basis — or even more frequently — were 1.4 to 1.9 times more likely to develop the cancer than controls, depending on the age at which the exams were done.

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The risk of brain tumor was also linked with panorex exams, which are taken outside the mouth and show all of the teeth on one piece of film. People who had exams when they were younger than 10 years old increased their risk of developing meningioma 4.9 times, and those who had the exams on at least a yearly basis were 2.7 to 3.0 times more likely to develop meningioma, depending on age, as controls.

Although the study recognizes the benefit of dental X-rays, the findings indicate that moderate use of X-rays should be considered.

"The American Dental Association’s guidelines for healthy persons suggest that children receive one X-ray every 1-2 years, teens receive one X-ray every 1.5-3 years, and adults receive one X-ray every 2-3 years," said Dr. Claus.

In 2006, the American Dental Association issued a statement that said there is little evidence to support the use of dental X-rays in all patients who are not experiencing any symptoms.

Meningioma tumors aren't usually malignant, but they can still cause disability and lead to life-threatening problems.

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