The thyroid gland, in the neck, is sensitive to ionising radiation, especially in children, but the potential risk posed by dental radiography is often ignored, researchers said.
In a study of 313 cancer patients, scientists from Brighton, Cambridge and Kuwait found the chances of developing cancer rose with increasing numbers of dental X-rays.
The researchers said the idea that dental radiography is absolutely safe merits further examination due to their findings.
They argued that their study drew attention to concerns that dental X-rays should only be prescribed to cater for a specific clinical need, rather than as part of a routine check-up.
About 1,900 new cases of thyroid cancer are diagnosed each year in Britain and the figures more than doubled between 1975 and 2006.
The researchers, led by Dr Anjum Memon, of the Brighton and Sussex Medical School, said the increasing use of sensitive diagnostic techniques does not necessarily account for the entire increase and that other causes warrant investigation.
They said the results of their work should be treated with caution because the data was based on self-reporting by the participants and comprehensive historical dental X-ray records were not available from the clinics.
Dr Memon said the findings were consistent with previous reports of increased risk of thyroid cancer in dentists, dental assistants and X-ray workers, suggesting that frequent low-dose exposures in adults may be significant.
Dental X-rays have also been linked with an increased risk of brain and salivary gland tumours, he added.
He said: “The public health and clinical implications of these findings are particularly relevant in the light of increases in the incidence of thyroid cancer in many countries over the past 30 years.”
The research was funded by the Kuwait Foundation for the Advancement of Sciences (KFAS) and was administered by the Kuwait University Research Grant Administration.