It also adds weight to the argument that dental X-rays should only be prescribed when there is a clinical need and not as part of a routine check-up.
The thyroid gland – which is in the neck – is known to be sensitive to ionising radiation, particularly in children, and dental radiography is often overlooked as a potential hazard to the gland, the team said.
The team from Brighton, Cambridge and Kuwait studied 313 thyroid cancer patients in Kuwait where the numbers of thyroid cancer are relatively high compared to Britain.
However although this is the largest case-control study on the subject, the researchers said it should be treated with caution as the data was based on self-reporting. They added that comprehensive historical dental X-ray records were not available from the clinics.
But 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 multiple low-dose exposures in adults may be important.
He added that dental X-rays have also been linked with an increased risk of brain and salivary gland tumours.
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.
‘It is important that our study is repeated with information from dental records including frequency of X-rays, age and dose at exposure.
‘If the results are confirmed, then the use of X-rays as a necessary part of evaluation for new patients, and routine periodic dental radiography, at six to 12 months interval, particularly for children and adolescents, will need to be reconsidered, as will a greater use of lead collar protection.’
He added: ‘The notion that low-dose radiation exposure through dental radiography is absolutely safe needs to be investigated further, as although the individual risk, particularly with modern equipment, is likely to be very low, the proportion of the population exposed is high.’