People who get regular dental X-rays are more likely to suffer a common type of brain tumor, U.S. researchers said on Tuesday, suggesting that yearly exams may not be best for most patients.

The study in the U.S. journal Cancer showed people diagnosed with meningioma who reported having a yearly bitewing exam were 1.4 times to 1.9 times as likely as a healthy control group to have developed such tumors.

A bitewing exam involves an X-ray film being held in place by a tab between the teeth.

Also, people who reported getting a yearly panorex exam -- in which an X-ray is taken outside the mouth and shows all the teeth on one film -- were

2.7 to three times more likely to develop cancer, said the study.

A meningioma is a tumor that forms in the membrane around the brain or spinal cord. Most of the time these tumors are benign and slow growing, but they can lead to disability or life-threatening conditions.

The research, led by Elizabeth Claus of the Yale University School of Medicine, was based on data from 1,433 U.S. patients who were diagnosed with the tumors between the ages of ages 20-79.

For comparison, researchers consulted data from a control group of 1,350 individuals who had similar characteristics but had not been diagnosed with a meningioma.

Dental patients today are exposed to lower radiation levels than they were in the past, but the research should prompt dentists and patients to re-examine when and why dental X-rays are given, said Claus.

"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," she said.

The American Dental Association's guidelines call for children to get one X-ray every one to two years; teens to have one every 1.5 to three years, and adults every two to three years.

The ADA said in 2006 there was little evidence to back up the routine use of full-mouth dental X-rays in patients without any symptoms.

Michael Schulder, vice chairman of the department of neurosurgery at Cushing Neuroscience Institute, part of the North Shore Long Island Jewish Health System in New York, said he was not shocked by the findings.

"This should come as no great surprise given the connection between radiation and meningioma development that has been established in various other contexts," said Schulder, who was not involved in the research.

"The chance of these tumors arising in patients who were X-rayed yearly still was low. Nonetheless, dentists and their patients should strongly consider obtaining X-rays less often than yearly unless symptoms suggest the need for imaging." (AFP)