Repeated exposures to dental X-rays may be associated with an increased risk of thyroid cancer and meningioma, according to researchers at the Brighton and Sussex Medical School (BSMS) in Brighton in the United Kingdom.
About 3,500 new cases of thyroid cancer and 1,850 cases of meningiomas are diagnosed each year in the United Kingdom. Meningiomas are tumors in the meninges layers of tissue, which surround and protect the brain and spinal cord. Most meningiomas are benign and grow very slowly.
The incidence of thyroid cancers and meningiomas have increased in many countries during the past three decades, the researchers report. Much of the increase in thyroid cancer rates is probably due to increased surveillance, screening, and over-diagnosis, the researchers said, but they believe other causes need investigation.
The thyroid gland’s location in the back of the neck and the meninges’ location in the brain and spinal cord leave these organs exposed to radiation from dental X-rays. Both organs are highly radiosensitive, particularly in childhood and adolescence. Dental radiography, a source of low-dose diagnostic radiation, often is overlooked as a potential hazard, the researchers said.
The researchers conducted a systematic review and meta-analysis that summarized the findings from all previously published studies on dental X-ray exposure and the risk of thyroid cancer, meningioma, and other cancers of the head and neck region.
The researchers said their results should be treated with caution because these studies did not include individual organ doses and ages at exposure and are subject to recall bias and other limitations. But they also said their synthesis provides good evidence to warrant more research based on dental X-ray records and patient follow-up to test the hypothesis further.
“Little is known about the impact and magnitude of risk associated with dental X-rays, which have been the fastest growing source of human exposure to low-dose ionizing radiation during the past three decades, with many patients being exposed to dental X-rays on multiple occasions over many years,” said professor Anjum Memon, chair in epidemiology and public health medicine.
“Given this high lifetime prevalence and frequency of exposure, even a small associated increase in cancer risk would be of considerable public health importance. The clinical and public health implications of these findings are relevant in light of the increasing incidence of thyroid cancer and meningioma in many countries,” Memon said.
“Our study highlights the concern that like chest or other upper-body X-rays, dental X-rays should be prescribed when the patient has a specific clinical need and not as a standard part of evaluation for new patients, for routine checkup, or for periodic screening for dental caries or decay in children and adolescents. Current UK, European, and USA guidelines stress the need for thyroid shielding during dental radiography,” he said.
“The findings also stress the need for maintaining comprehensive long-term dental X-ray records, which could follow the patient when they register with a new dentist, thus avoiding the need for unnecessary X-rays,” he said.
“The notion that low-dose radiation exposure through dental radiography is completely without risk needs to be investigated further. Although the individual risk with modern technology and equipment is likely to be very low, the proportion of the population exposed is high,” Memon said.
“Considering that about one-third of the general population in developed countries is routinely exposed to one or more dental X-rays per year, these findings manifest the need to reduce diagnostic radiation exposure as much as possible,” he said.