New Dental X-ray Guidelines Spell Out Radiation Reduction

Laird Harrison

February 11, 2013

Dentists who ignore the new American Dental Association (ADA) and US Food and Drug Administration (FDA) guidelines on radiography may be putting their patients at unnecessary risk, experts told Medscape Medical News this week.

Published in November 2012, the guidelines update the ADA-FDA's 2004 recommendations and, for the first time, offer detailed methods for limiting patients' exposure to radiation.

"As practitioners we need to follow the ADA-FDA guidelines because it is the right way to treat our patients," John Ludlow, DDS, a professor of oral radiology at the University of North Carolina, Chapel Hill, told Medscape Medical News in an email. "It's the way that I would want (and ask) to be treated as a patient."

Radiation from dental imaging has attracted more controversy in recent years as computed tomography (CT) scans become more common in dentistry and as more becomes known about radiation's long-term effects.

A study published in the September 2012 issue of Cancer showed an association between dental X-rays and incidence of meningioma, a common benign brain tumor. Three letters published in the January issue of the journal challenged the findings.

Beyond schedules for when to administer routine X-rays, the new ADA-FDA guidelines provide specific instructions for limiting patients' exposure to radiation.

In a key change, the new guidelines support rectangular collimation. Where the 2004 guidelines simply recommend "collimation of the beam to the size of the receptor whenever feasible." The updated ones argue, "Since a rectangular collimator decreases the radiation dose by up to fivefold as compared with a circular one, radiographic equipment should provide rectangular collimation for exposure of periapical and bitewing radiographs."

Rectangular collimation can also improve contrast by reducing fogging caused by secondary and scattered radiation, the new guidelines note.

"The recommendation on rectangular collimation is not widely followed, largely due to the misconception that the smaller X-ray beam area will result in misalignment errors that will necessitate retaking of images," said Dr. Ludlow, who is on the ADA Council on Scientific Affairs but did not participate in drafting the new guidelines.

"While errors do occur in increased numbers with rectangular collimation, these are largely cosmetic in character and do not result in a significant loss of diagnostic information that would necessitate retaking of the image."

Other recommendations include:

  • "The position-indicating device should be open ended and have a metallic lining to restrict the primary beam and reduce the tissue volume exposed to radiation.

  • Use of long source-to-skin distances of 40 cm, rather than short distances of 20 cm, decreases exposure by 10 to 25 percent. Distances between 20 cm and 40 cm are appropriate, but the longer distances are optimal.

  • The use of F-speed film can reduce exposure 20 to 50 percent compared to use of E-speed film, without compromising diagnostic quality.

  • [R]are-earth intensifying screens are recommended because they reduce a patient's radiation exposure by 50 percent compared with calcium tungstate-intensifying screens.

  • Holders that align the receptor precisely with the collimated beam are recommended for periapical and bitewing radiographs.

  • Dental professionals should not hold the receptor holder during exposure.

  • The optimal operating potential of dental x-ray units is between 60 and 70 [peak kilovoltage].

  • Size-based technique charts/protocols with suggested parameter settings are important for ensuring that radiation exposure is optimized for all patients."

Most changes to the guidelines shift nuance rather than offering completely new techniques. For example, in addressing use of lead aprons, the 2004 guidelines say, "Because every precaution should be taken to minimize radiation exposure, protective thyroid collars and aprons should be used whenever possible. This practice is strongly recommended for children, women of childbearing age and pregnant women."

The new version says, "If all the recommendations for limiting radiation exposure are put into practice, the gonadal radiation dose will not be significantly affected by use of abdominal shielding. Therefore, use of abdominal shielding may not be necessary."

However, the new guidelines retain the recommendation to use a thyroid collar.

Dr. Ludlow said many dentists are not following best practices in reducing patients' radiation exposure. "While many practitioners have switched to digital imaging technologies, the majority of those still using intraoral film are utilizing slower D speed, rather than the faster F speed alternative," he said.

"This is due to the mistaken belief that D speed film provides better image quality. Scientific studies have consistently demonstrated that there are no significant differences in diagnostic efficacy when using the faster film."

Some dentists also mistakenly believe that they have lowered their patients' radiation dose simply by shifting from film to digital radiography, said Allan G. Farman, BDS, PhD, MBA, DSc, a professor of oral and maxillofacial radiology and imaging at the University of Louisville, Kentucky, who was not involved in revising the guidelines.

"It's possible with [complementary metal-oxide-semiconductor] and storage phosphate to overexpose the patient," he told Medscape Medical News. "Digital does not always mean less radiation. If improperly used, it can mean higher doses."

Dr. Farman and Dr. Ludlow have disclosed no relevant financial relationships.

"Dental Radiographic Examinations: Recommendations for Patient Selection and Limiting Radiation Exposure." American Dental Association and US Department of Health and Human Services. Full text

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