Dental x-rays linked to tumors?

A recent School of Medicine study on dental x-rays is drawing fierce debate among the medical community.

The study, led by Yale School of Public Health Director of Medical Research Elizabeth Claus, found a correlation between non-cancerous brain tumors and exposure to dental x-rays. The study found that patients diagnosed with such tumors were likely to have been exposed to an above average amount of dental x-rays, said Margaret Wrensch, professor in residence of neurological surgery at the University of California, San Francisco. Since the study was published April 10 in the medical journal Cancer, it has drawn criticism from the American Academy of Maxillofacial and Oral Radiology for its methods of data collection and potential inconsistencies in its findings.

“The study highlights the need for increasing awareness regarding the optimal use of dental x-rays, which unlike many risk factors, is modifiable,” Claus was quoted as saying in a press release from the University. Claus could not be reached for comment.

The study relied on interviewing patients with meningioma, a non-cancerous form of brain tumor that can have debilitating effects on vision and motor function, Wrensch said. She added that meningioma patients were twice as likely as those without meningioma to report having undergone regular bitewing exams, a form of dental x-ray that examines one portion of the mouth in detail rather than the whole.

Wrensch said the implications of the study don’t mean that people should abandon dental x-rays. She said the study suggests instead that patients be cautions when considering x-rays, and try to limit their exposure to one x-ray every few years instead of a yearly exam. In addition, she said, the study shows the effects of older forms of x-ray exams, since the mean age of patients was 57, but the amount of radiation in modern x-rays is much less than it was in the past.

However, the study has draw criticism from some experts. Alan Lurie, president of the American Academy of Oral and Maxillofacial Radiology, said the study was rife with “severe internal inconsistencies.” He said such inconsistencies resulted from two problems: the study’s reliance on participants’ memory and reported discrepancies between smaller and larger doses of radiation.

Lurie emphasized the second internal inconsistency as the most important flaw in the study. Although the report found that bitewing dental exams were associated with high incidents of tumor growth, he noted that full-mouth x-rays, which deliver a higher dosage of radiation than bitewing exams, were not strongly correlated with tumors. A full mouth exam is the equivalent of 20 bitewing exams, Lurie said, adding that this discrepancy is enough to debunk the study’s results.

“To me, as a radiation biologist, this pretty much invalidates the entire study,” Lurie said.

Wrensch said the study had no clear answer to the problem Lurie raised about the discrepancy between low and high-dose x-rays. She suggested that the higher incidence of correlation might be due to the fact that bitewing exams are more common than full mouth exams, but said she couldn’t give a “hard and true” answer to Lurie’s concern.

With regard to memory, Lurie said the study could be biased both by forgetfulness of its subjects over age 50 and interviewers’ implication that dental x-rays could play a role in tumor development. For example, the researchers might have primed the meningioma patients to expect that their condition could be associated with x-rays.

In response to this, Wrensch said the risk of relying on memory is one that researchers are well aware of, and one that was discussed in the study itself. She added that the study compared reports of various kinds of x-rays using a control group along with the actual group of patients, and that the bitewing exam was the only one for which a much higher incidence of exams was reporter for the meningioma patients than in the control group. This suggests that, for the bitewing exam specifically, reports of memory were accurate.

Modern bitewing x-rays deliver a relatively small dose of radiation: .04 MilliGrays. For comparison, the average person is exposed to 3.1 MilliGrays of cosmic background radiation simply by living in the United States for one year.

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