CADTH Examines Cancer Risk from Dental X-rays

There may be an association between dental x-rays and certain types of cancer, according to a recent review by the Canadian Agency for Drugs and Technologies in Health (CADTH). CADTH’s review highlights the importance of weighing the benefits of dental x-rays against the risk of patient exposure to x-rays, which can have a cumulative effect from multiple sources over time. This risk assessment, guided by the ALARA (as low as reasonably achievable) principle, should ensure that patient radiation doses are minimized, but diagnostic information is maximized.

Although radiation doses from dental x-rays are low and have decreased over the years—thanks to the use of faster, more sensitive film emulsions, newer technologies and better radiation protection measures (including the use of evidence-based radiographic selection criteria)—they remain a public health concern because of the prevalence and frequency of dental x-rays.

Based on data from 8 case-control studies that assessed the association between exposure frequency to dental x-rays and brain tumours (5 reports), thyroid cancer (1 report), breast cancer (1 report), or pediatric cancer of connective tissues (1 report), the CADTH review presents some evidence that dental x-rays may increase the risk for cancer. But, given the limitations of the studies used in CADTH’s review, the agency acknowledges that its conclusion should be interpreted with caution and is not proof of cause and effect. The study limitations include:

• All data on x-ray exposure frequency from decades earlier was self-reported; only one study verified exposure history, using dental records, but only for a subset of patients.
• The association between x-rays and cancer could be substantially overestimated if patients who had developed cancer were more likely than controls to recall their history of x-ray exposure frequency.
• The ability of cancer patients, particularly those with brain tumours, to accurately recall their history of x-ray exposure frequency may have been affected by the disease or disease treatment.
• For studies that examined the frequency of different types of dental x-rays, patients may have had difficulty in distinguishing between each type of x-ray (e.g. bitewing versus full mouth x-rays).

Dr. Ernest Lam, associate professor and head of oral and maxillofacial radiology/biological and diagnostic sciences at the University of Toronto faculty of dentistry and jcda.ca editorial consultant, co-authored a statement on behalf of The American Academy of Oral and Maxillofacial Radiology (AAOMR) that expressed concerns about methodological weaknesses in one of the studies included in the CADTH review. The study¹reported an association between dental x-rays and an increased risk of brain cancer. AAOMR’s statement noted the study’s potential limitations: “A number of irreconcilable data collection and consistency problems highlight serious flaws in the study and render the conclusions invalid.”

Given the questions raised about the validity of at least one study included in the CADTH review, what do the review’s results mean for dentists? The guidance for patient protection in the CDA Position Statement on Control of X-Radiation in Dentistry indicates that, “The exposure to the patient should be kept as low as reasonably achievable but at the same time provide an adequate radiological examination capable of providing an accurate diagnosis.” One of the most important practices of the ALARA principle in dentistry is the responsible ordering of dental radiographs, which should only be ordered only after a complete clinical examination and should follow evidence-based guidelines².