Letters: ‘No evidence’ of risk
June 18, 2012
Elizabeth B. Claus, M.D., et al., presented a case-control study in which they examined the association between dental X-rays and the risk of intracranial meningioma ("Dental X-rays and Risk of Meningioma," Cancer. 2012 DOI: 10.1002/cncr.26625).
While there is strong evidence that ionizing radiation may cause cancer, the question remains whether low doses lead to a detectable increase in risk. Regarding dental X-rays, the effective dose is far below the yearly exposure received from natural background radiation. In the present case, the cerebral region is not even within the primary radiation field. It is thus most disturbing that the authors do not consider doses.
The results suggest a twofold increase in risk if the subject had at least one bitewing in his entire life. However, Table 2 shows that both cases and controls report this case with nearly the same (high) relative frequencies: 95.8 percent and 92.2 percent, respectively. The authors seem to have missed the fact that the odds ratio may not simply be translated into relative risks if high probabilities are regarded (Davies H.T., et al. "When Can Odds Ratios Mislead?" British Medical Journal 316, 989-991m; 1998).
The article postulates a nearly fivefold increase in risk for subjects who got at least one panorex film at ages under 10 years, based on recalls by 22 out of 1,433 patients and five out of 1,350 controls (average age: 57.5). Recalls are fairly unreliable and prone to personal bias if events are affected that took place five decades ago. Thus, these small numbers do not allow a reliable estimation of the risk.
Results for full-mouth films suggest smaller risks (not even statistically significant) than for the before mentioned cases. A full-mouth series consists of 16-20 single films and thus exposes the patient to a dose which is larger by one order of magnitude than with a single film and still considerably larger than that obtained with a panorex. In summary, the article suggests that relatively large doses do not lead to a significant increase in risk while much smaller doses do.
In conclusion, the study provides little to no evidence of an increased risk of meningioma for subjects exposed to low-dose dental X-ray diagnostics.
Dieter Dirksen, Ph.D.
Ludger Figgener, M.D., D.M.D., Ph.D.
University of Muenster
Department of Prosthetic
Editor’s note: The ADA News reported on the Cancer study in the April 23 issue, "Experts Question X-ray Study."