People who have had a history of frequent dental x-rays, particularly at a young age, have an increased risk of developing meningioma, the most common type of brain tumor in the United States.

"This research suggests that although dental x-rays are an important tool in maintaining good oral health, efforts to moderate exposure to this form of imaging may be of benefit to some patients," researcher Dr. Elizabeth Claus, a neurosurgeon at Brigham and Women's Hospital, in Boston, and the School of Medicine at Yale University in New Haven, said in a statement released by the hospital on Tuesday.

A meningioma, which accounts for about 33 percent of all primary brain tumors, arises from the membranes that surround the brain and spinal cord. While most meningiomas are benign, rarely the tumor can be malignant, and some can be classified as being between a noncancerous or cancerous tumor.

While meningiomas typically occur in older women, these brain tumors can occur in males at any age, including childhood, but these tumors remain poorly understood, partly because meningioma was only added to brain tumor registries in the U.S. in 2004.

Ionizing radiation, which is found in X-rays, is an environmental risk factor for this type of cancer, and routine dental X-rays are the most common source of this type of radiation for most healthy people in the U.S.

Claus and her colleagues compared self-reported dental histories of 1,433 patients diagnosed with meningioma tumors between the ages of 20 and 79 between 2006 and 2011 to a matched “control group” of 1,350 healthy individuals.

 The findings show that tumor patients were twice more likely to report having a "bitewing" X-ray and those who reported having them yearly or on a more frequent basis were 1.4 to 1.9 times more likely to develop meningioma compared to the control group. 

Bitewing X-ray, which uses an X-ray film clenched between the teeth in a tab of plastic or cardboard, and can check for decay between the teeth and bone loss caused by gum disease. 

Researchers found an even greater increased risk of meningioma linked to patients who used "panorex", or "panoramic" X-rays that show a broad view of the jaw, teeth, and nasal area and reveals problems like impacted teeth, cysts, infections and bone abnormalities. 

The findings show that there was a five times greater chance of developing meningioma in people who had panorex X-rays when they were younger than 10 years old.

Claus and her research team said that having X-rays once a year or more often was associated with a 2.7 to three times increased risk in developing cancer, depending on age. 

"Our findings suggest that dental X-rays, particularly when obtained frequently and at a young age, may be associated with an increased risk of intracranial meningioma, at least for the dosing received by our study participants," the study authors wrote. 

However, they noted that radiation from dental X-rays today are lower than before, and because there was a broad range of ages between patients in the study, some participants may have been exposed to higher radiation doses earlier in their lives. 

Most research on the link between ionizing radiation and meningioma has largely focused on high exposure levels from atomic bombs or cancer treatments, and while past studies have found a slight increased risk from dental X-rays, they were limited by a small pool of participants who may have receiver much higher radiation doses, according to researchers from the latest study.

Experts say that tumors typically type 20 to 30 years to develop after exposure to an environmental pollutant like radiation, and tumors can grow larger than a baseball and can cause headaches, vision and speech problems and loss of motor control.

The American Dental Association recommends that dentists be cautious in their use of X-rays and suggest that X-rays be given to children who do not have an increased risk of developing cavities X-rays every one to two years, adolescents every year and a half to three years and adults every two to three years. 

“[T]he results rely on the individuals’ memories of having dental x-rays taken years earlier. Studies have shown that the ability to recall information is often imperfect,” the ADA said in a statement noting the study’s limitations and to encourage further research.  “Also, the study acknowledges that some of the subjects received dental x-rays decades ago when radiation exposure was greater. Radiation rates were higher in the past due to the use of old x-ray technology and slower speed film.”

“Don’t panic and don’t not go to the dentist,” Claus said stressing that she does not want the findings to send an alarmist message, “But do look into the guidelines and talk with your dentist.”

“It’s worth having that conversation,” she added.

The findings were published early online in the journal Cancer.