Background: Exposure to moderate-to-high doses of ionizing radiation is the only 
established environmental risk factor for thyroid cancer and brain and central 
nervous system tumors. Considering the high lifetime prevalence and frequency of 
exposure to dental X-rays, the most common source of diagnostic radiation 
exposure in the general population, even a small associated increase in cancer 
risk would be of considerable public health importance. With the objective to 
inform clinical practice and guidelines, we synthesized the current 
epidemiological evidence on the association between dental X-rays and the risk 
of thyroid cancer, meningioma, and other cancers of the head and neck region. 
Methods: The Medline, Embase, and Web of Science databases were searched to 
identify eligible studies. Summary odds ratio/relative risk estimates and 
confidence intervals were extracted, and pooled risk ratios (RRs) for each 
cancer were calculated using random effects meta-analysis. Results: The 
literature search identified 5537 publications; of these, 26 studies including 
10,868 cancer patients were included in the synthesis. The random effects 
meta-analyses, based on seven studies of thyroid cancer (six case/control, one 
cohort) and eight studies of meningioma (all case/control), showed that multiple 
(or repeated) exposures to dental X-rays were significantly associated with an 
increased risk of thyroid cancer (pooled RR = 1.87 [95% confidence interval, CI 
1.11-3.15]) and meningioma (pooled RR = 1.53 [CI 1.26-1.85]). There was no 
association with glioma, and there were too few studies of other cancers of the 
head and neck region to conduct a meaningful meta-analysis. Conclusions: Based 
on a meta-analysis of retrospective case/control studies, these findings provide 
some support to the hypothesis that multiple (or repeated) exposures to dental 
X-rays may be associated with an increased risk of thyroid cancer and 
meningioma. These studies did not include individual organ doses and ages at 
exposure, and are subject to recall bias and other limitations. Furthermore, the 
thyroid exposure has decreased dramatically over time from the use of thyroid 
shields and improved technology/equipment. Prospective studies, based on dental 
X-ray records and patient follow-up, are needed to test the hypothesis further 
and clarify the possible cancer risk associated with dental radiography, as 
although the risk at the individual level, particularly with improved 
technology/equipment, is likely to be very low, the proportion of the population 
exposed is high. 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.