Experts question X-ray study
April 13, 2012
By Jean Williams, ADA News staff
A study published online April 10 associating dental radiographs with brain tumors has stirred media attention and questions from experts on the study’s methodology.
The study published in Cancer, an American Cancer Society peer-reviewed journal, found that people with meningiomas (typically benign brain tumors) are more likely to report that they’ve had certain dental X-ray examinations in their lifetimes.
In a press statement following publication of the study online by Cancer, the ADA referred to ADA recommendations for prescribing radiographs, which help dentists determine how to keep radiation exposure as low as reasonably achievable.
“The ADA has reviewed the study and notes that the results rely on the individuals’ memories of having dental X-rays taken years earlier,” said the April 10 statement. “Studies have shown that the ability to recall information is often imperfect. Therefore, the results of studies that use this design can be unreliable because they are affected by what scientists call 'recall bias.’”
The ADA released its statement in tandem with the lifting of the press embargo on the study. U.S. News and World Report and MSNBC interviewed Dr. Matthew Messina, a practicing dentist in Ohio and an ADA media spokesperson. Several other media outlets cited the ADA’s recommendations on dental X-rays, which can be viewed at ADA.org. (Click the Public Resources tab, Oral Health Topics, Radiography/X-ray and Dentist Version to find The Selection of Patients for Dental Radiographic Examinations.)
In “Dental X-rays and Risk of Meningioma,” the authors, led by researcher and neurosurgeon Elizabeth B. Claus, M.D., of Yale University School of Medicine and Brigham and Women’s Hospital, conclude that “exposure to some dental X-rays performed in the past, when radiation exposure was greater than in the current era, appears to be associated with an increased risk of intracranial meningioma.”
Using anecdotal evidence, the population-based, case-control study compared dental and therapeutic radiation histories in 1,433 patients who had intracranial meningiomas diagnosed between ages 20 and 79 with a control group of 1,350 patients. Data collection involved interviews and questionnaires and relied on the patients’ recall of details related to dental care received over their lifetimes.
According to the study report, “Participants were asked to report the number of times they had received bitewing, full-mouth, or panoramic films” during four stages in life: before age 10, between ages 10 and 19, between ages 20 and 49, and up to age 50.
Dr. Alan G. Lurie, a radiation biologist and head of radiology at the University of Connecticut School of Dental Medicine, has many concerns about the study’s design and outcomes. “I think it is a very flawed study,” said Dr. Lurie, who is also president of the American Academy of Oral and Maxillofacial Radiology.
He characterized at least one outcome of the study—reflected in a table that related meningioma risk to types of dental X-ray examination—as “radiobiologically impossible.”
Said Dr. Lurie, “They have a table, Table 2, in which they ask the question, 'Ever had a bitewing,’ and the odds ratio risk from a bitewing ranges from 1.2 to 2.0, depending on the age group. Then they asked 'Ever had full mouth’ series, and the odds ratio risk from a full mouth series ranged from 1.0 to 1.2.
“That is biologically not possible because the full mouth series has two to four bitewings plus another 10 to 16 periapicals. A full mouth series, just to round things off, is 20 intraoral X-rays of which two to four are bitewings. They are showing that one bitewing has 50 to 100 percent greater risk than a full mouth series that has multiple bitewings plus a bunch of other films.”
Explaining this gross internal discrepancy is difficult, as the epidemiologic and statistical methods are widely accepted, Dr. Lurie said. He attributes the perceived discrepancy in the data to possible recall bias in the patients involved in the study.
“Epidemiologists are very aware of this bias,” Dr. Lurie said. “What happens is you’re asking people to remember what kind of dental X-rays they had 10, 20, 30 or 40 years ago, and how frequently they had those X-rays. It’s anecdotal, and the argument is that it’s just as anecdotal for the group without meningiomas as it is for the group with meningiomas. That is not necessarily true.”
Individuals who had meningiomas and had surgery for them in this study population may be more likely to remember having had X-rays than individuals who did not have meningiomas, Dr. Lurie said.
Dr. Lurie emphasized that his comments on the dental X-rays study are his own.
In addition, AAOMR’s official statement similarly took issue with the study’s validity. Dr. Ernest Lam, associate professor of oral and maxillofacial radiology/biological and diagnostic sciences at University of Toronto Faculty of Dentistry, and Dr. Jie Yang, professor of oral and maxillofacial radiology at Temple University Kornberg School of Dentistry, are the statement’s authors.
“A number of irreconcilable data collection and consistency problems highlight serious flaws in the study and render the conclusions invalid,” the AAOMR statement concluded.
The statement also said: “Absorbed doses from dental radiography have declined upwards of 60 percent in recent years as a result of faster X-ray film speed, the development of digital sensor technology, X-ray beam collimation and patient shielding. Given that these and other factors were not known to the subjects or reported, it is impossible to recreate a dose-response relationship between the radiation doses subjects received and the development of meningioma.”
View the AAOMR statement online.
A broad range of local, national and international media reported news of the dental X-rays study, including ABC World News with Diane Sawyer, CBS This Morning, Good Morning America, USA Today, The Sun (United Kingdom), The Daily Mail (United Kingdom) and others.
The study can be viewed online free of charge online.
The ADA in November 2010, with the support of an educational grant from Schick Technologies Inc., distributed Safe Use of Radiographs in Dentistry, a full-color poster that ADA members can order free from schicktech.com or by calling Emily Brown at 1-718-482-2131.
Also, members may take the ADA Online CE course: Radiographic Examinations: Choosing the Right Patients and Equipment, which can be accessed at adaceonline.org.
Visit MouthHealthy.org for additional resources on dental X-rays.