TORONTO – A new study is urging the public to discuss just how often routine dental X-rays should be carried out, but Canada’s top dental body says the U.S. research simply underscores a decreasing and well-know risk associated with the procedure.

A study published in the American journal “Cancer” on Tuesday found people who frequently had certain dental X-rays in the past — when radiation doses were higher — were linked to an increased risk of a common, but usually non-cancerous, brain tumour.

While the results of the study aren’t mean to alarm people into abandoning dental X-rays altogether, researchers at Yale University want people to re-think how often they get the procedure done.

They said their findings are important because dental X-rays are the most common artificial source of exposure to ionizing radiation for people living in the U.S. — a form of radiation which is a known risk factor for certain brain tumours.

“Although dental X-rays are an important tool in well selected patients, efforts to moderate exposure to (ionizing radiation) to the head is likely to be of benefit to patients and health care providers alike,” the authors of the study wrote.

Meanwhile, the Canadian Dental Association said the radiation risk associated with dental X-rays is well known and the procedure is only carried out when a patient needs it. Even then, the association said, the procedure delivers just a small amount of radiation.

“The most useful thing (about the study) is that it reminds everyone to use X-rays in a responsible fashion,” said Dr. Benoit Soucy, the association’s director of clinical and scientific affairs.

“We’ve simply continued to implement the principle that you only take X-rays when they are needed and you use as little radiation as you can when you generate that X-ray.”

To put the risk in context, Soucy said the radiation levels patients are exposed to during dental X-rays are dropping every year, particularly ever since dentists swapped film for digital images.

“The exposure that is used in dental X-rays is very small, you can compare that to the amount of radiation that you’re exposed to on a transatlantic flight,” he said, explaining that higher altitude and less filtered exposure to the sun’s rays increase the amount of radiation flyers are exposed to.

How often a Canadian gets a dental X-ray depends on their oral health, but a person whose mouth is in good condition might get one every few years.

“It would not be on a yearly basis,” said Soucy, adding that dentists now often refer back to past X-ray images while treating patients, cutting down the frequency of the procedures even further.

The researchers at Yale studied 1433 patients between 2006 and 2011 who had been diagnosed with intracranial meningioma — a common kind of brain tumour which often turns out to be benign.

All patients were between 20 and 79 years when diagnosed and lived in the United States. A control group of 1350 people matched on age, sex and geography was used for the study.

Researchers found that those with the tumours were more than twice as likely to have had a bitewing dental X-ray — where an X-ray film is held in place by a tab between a patient’s teeth.

The study also found an increased risk of the brain tumours was associated with those who had panorex X-rays at a young age, a yearly basis or with greater frequency. The procedure is when an X-ray is taken outside the mouth and shows all teeth on one film.

A feature of the study worth noting is that it’s based on procedures which have seen radiation exposure levels drop in recent years. Given the technological advances in dental X-rays, the results of the study do not paint a picture of present risks, but rather suggest an image of the risks of the past.

Researchers also noted that a limitation of the study was that patients had to use their memory to recall having the procedures done — something which may have led to under or over reporting of dental X-rays carried out.

The way in which the study generated its results caused Soucy to advise caution when digesting the data.

“You simply have to be careful in the way you look at those results and not take those numbers as precise numbers,” he said.

“If there’s a good reason to take a dental X-ray, dental X-rays are overall safe and the fear of radiation exposure should not keep you from having a useful X-ray taken.”

The Canadian Cancer Society advised anyone concerned with medical radiation from an X-ray to talk to their healthcare professional.

“Similar to other medical tests there are risks and benefits associated with X-ray use,” said Gillian Bromfield, the society’s director of Cancer control policy.

“When using tests that require medical radiation, every care should be taken by dental professionals to minimize, if not eliminate, risk to the patient, and only use the tests when necessary.”