People who get regular dental x-rays are more likely to suffer a type of brain tumour, according to new research, suggesting that yearly exams may not be best for most patients.
The study in the US 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 tumours.
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 tumour that forms in the membrane around the brain or spinal cord. Most of the time these tumours 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 1433 US patients who were diagnosed with the tumours between the ages of ages 20 and 79 years.
For comparison, researchers consulted data from a control group of 1350 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, says 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 says.
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, says 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," says Schulder, who was not involved in the research.
"The chance of these tumours 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."
Weighing up the risk
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.
Associate Professor Matthew Hopcraft of the University of Melbourne Dental School says there are no strict guidelines regarding dental x-rays in Australia.
"Dentists in Australia would normally do a risk assessment for their patients ... weighing up the risk of disease versus the risk of potential harm from radiation from the x-rays," says Hopcraft.
He says most patients would undergo one x-ray every one or two years, while a patient with a high risk from tooth decay would need one every six months.
Hopcraft says improvements in radiographic equipment has seen the dosage rate received by patients undergoing an x-ray reduce over time.
"We've moved a lot in Australian practice towards digital radiography from traditional film and that's allowed the dosage of radiation to decrease significantly as a consequence."