Dental X-Rays And The Risk Of Cancers Of The Head And Neck Region: A Systematic Review And Meta-Analysis

Josefin SUNDIN, Brighton and Sussex Medical School, United Kingdom

1 Division of Primary Care and Public Health, Brighton and Sussex Medical School, Brighton, UK

Dental radiography, a common source of low-dose diagnostic radiation exposure in the general population, has been associated with the risk of thyroid cancer and tumours of the salivary glands and brain. We synthesised the published data to assess the association between dental x-rays and risk of developing these cancers.  
We carried out a systematic literature search of observational epidemiological studies from inception up to 2 November, 2015 using electronic databases Embase (Ovid), Medline (Ovid and PubMed) and Web of Science. Studies were eligible for inclusion if they reported the association as an odds ratio/relative risk, or contained sufficient information for calculating the effect size. Meta-regressions were fitted using the statistical software Stata. Heterogeneity was assessed with I2 and Cochran’s Q. Quality of the studies was assessed using the Newcastle-Ottawa Scale.
The literature search identified 1319 articles; of these, 71 were obtained in full text for further assessment, and 23 were selected for inclusion in the synthesis. Six studies assessed the association with thyroid cancer, three with tumours of the salivary glands, six with glioma, and eight with meningioma. The meta-regression analysis showed that exposure to dental x-rays was significantly associated with an increased risk of thyroid cancer (OR=1.74, 95% CI: 1.34-2.26). An increased risk of meningioma (based on 3 studies) was observed for repeated (5+) dental x-rays (OR=1.62, 95% CI: 1.14-2.30). There was no significant association with any other cancer of the head and neck region.
Our review further supports the existing hypothesis that exposure to dental x-rays is associated with an increased risk of thyroid cancer. Although the risk at the individual level is likely to be low, the proportion of the population exposed is large. Thus, the notion that low-dose radiation exposure through dental radiography in the general population is safe warrants further investigation.