Dental experts fault study linking X-rays to term low birth weight
San Antonio (June 7, 2004) – A study published April 28 in the Journal of the American Medical Association (JAMA) is causing some pregnant women to question whether they should have X-rays taken in their dentists’ offices. The study raises undue concern about the safety of dental radiography during pregnancy, said William Moore, D.D.S., and John W. Preece, D.D.S., of the Dental School at The University of Texas Health Science Center at San Antonio.
Dr. Moore, assistant professor of dental diagnostic science and head of the division of maxillofacial radiology, and Dr. Preece, professor of dental diagnostic science, have written a response to the study and submitted it to the JAMA. The response also has been accepted for publication in the Journal of the American Dental Association.
“The knee-jerk reflex is to think that radiation used in dentistry is harmful,” Dr. Preece said. “The public should know that the potential radiation risk a patient may experience in the dentist’s office is equivalent to only three to five days of normal ‘background’ radiation in our country (background radiation is radiation we receive from outer space, soil and building materials, and the food we eat). The risk of harmful effects such as cancer and birth defects after dental X-rays is miniscule and certainly does not equal the health benefits of good oral care.”
The study in the JAMA was reported in the May 10 issue of TIME magazine under the headline “Dare you see your dentist again?” The study compared 1,117 women who delivered low birth weight infants at term and 4,468 women who delivered normal birth weight infants. Women were grouped according to the level of dental radiographic exposures they received. The authors estimated that eliminating dental radiographs during the first trimester could reduce the incidence of term low birth weight infants by “up to 5 percent.”
Dr. Preece pointed out that 85 percent of the mothers with term low birth weight babies in the study had no identifiable dental radiographic exposure. “Thus, the benefit of a possible 5 percent decrease in term low birth weight would really affect only three babies out of the study group,” he said.
Drs. Moore and Preece said that in the last century of research, no other authors have been able to demonstrate cancer or other biological effects at the low levels of radiation exposure reported as being significant in the study. The study also did not consider possible non-dental, medical radiation exposure as a contributing factor to term low birth weight infants, “a significant oversight and another potential flaw in the study,” Dr. Preece said.
Dental X-rays are measured in units called milligrays (mGy). The effective dose (the amount of radiation from a full-mouth dental radiographic survey) is less than 0.0003 mGy when the dentist uses the lead apron to shield patients, compared to the 3 mGy in background radiation absorbed annually by everyone in the United States.
“As a point of reference, various localities around the world with large populations have background radiation levels averaging 15 to 40 mGy a year with no known harmful effects, including Ramsar, Iran, where an individual was found to have an annual dose of 132 mGy, or 0.36 mGy per day,” Drs. Moore and Preece wrote.