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Inside Dentistry

January 2013, Volume 9, Issue 1
Published by AEGIS Communications


Radiationin Dentistry

What can dentists do to minimize patients’ exposure?

By Ellen Meyer

Despite public concern about medical/dental radiation exposure, the American Nuclear Society website makes it clear that humans live in a radioactive world in which they receive exposure from many sources “from materials in the earth itself, from naturally occurring radon in the air, from outer space, and from inside our own bodies as a result of the food and water we consume.”1

The site features a link to an interactive table that makes it possible for individuals to calculate their annual “dose” including natural sources related to cosmic and terrestrial radiation as well as from medical diagnostic tests, airport security and air travel, power lines, computers, and televisions.

ADA Position

Natural or not, many patients are concerned about radiation exposure from dental x-rays, and the ADA position conveyed in a November 23, 2010, press release is that the ordering of diagnostic radiation procedures for patients should occur only if absolutely necessary for diagnosis and treatment and that dentists should apply the ALARA principle —As Low as Reasonably Achievable—to reduce radiation exposure to their patients by: “determining the need for and type of radiographs to take; using ‘best practices’ during imaging, including the application of quality control procedures; and, interpreting the images completely and accurately.”2

As summarized by the ADA’s Council on Scientific Affairs report, The Use of Dental Radiographs: Update and Recommendations: “Dentists should weigh the benefits of dental radiographs against the consequences of increasing a patient’s exposure to radiation, the effects of which accumulate from multiple sources over time.”3

Reducing Exposure

Since 1989, the ADA has published recommendations that promote reduced radiation exposure, such as the use of abdominal shielding and thyroid collars, on all patients when feasible, but especially for children, women of childbearing age, and pregnant women. The ADA also recommends that dentists use the fastest image receptor compatible with the diagnostic task, which should be no slower than E-speed film.2 The FDA, too, supports the use of faster x-ray film in the dental office, concluding that “E- and F-speed film products offer significant exposure reduction compared with D-speed film, cost approximately the same, and offer comparable clinical benefits” and urging dentists who have not yet made the switch to do so to reduce their patients’ radiation exposure.4

Lola Giusti, DDS, is Coordinator of Radi­ology Clinical Services in the Arthur A. Dugoni School of Dentistry at the University of the Pacific in San Francisco, California. She says that patients want to know they are receiving as little radiation as possible. Among the simplest precautions they can take, she says, is not only using thyroid collars, but making sure all staff members know how to adjust them properly. “It’s very important to use that thyroid collar and make sure it’s snug against the neck.”

Rectangular Collimator

Giusti is especially bullish on the use of the rectangular collimator, a device that latches onto any round-headed long-cone x-ray unit and restricts the beam. “The collimator changes the shape of the beam from having a beam like a flashlight to having a very directed narrow beam that’s about the shape and size of the film or sensor that goes into the patient’s mouth.” She urges colleagues to make this simple change that she says, according to the American Academy of Oral and Maxillofacial Radiology (AAOMR), reduces radiation in a full-mouth series from about 0.170 microsieverts (mSv) down to about 0.035 mSv. She does note that the collimator, which directs the beam and minimizes scatter, produces a more restricted beam. The implementation of the collimator requires that the operator use more care in placement of the x-ray head, and that it’s not for all patients. “We use it on as many patients as we can here in the dental school—about 90%; however, for patients who have extremely long roots or a severe gagging problem, we have to use the round collimator.” Nevertheless, she considers use of the rectangular collimator to be “the single biggest step that general practitioners can take to minimize radiation exposure to their patients.”

Digital Radiography

An initially more expensive measure Giusti supports is making the transition to digital radiography, whose many benefits include reducing radiation exposure. Citing figures from an article by Frederiksen,5 she says that depending on the number of images taken digital radiography can cut radiation exposure by one third compared with conventional film imaging. Using the rectangular collimator can reduce this exposure even further. “An FMX taken with a round collimator has an average exposure of 170 mSv. The same FMX taken using a rectangular collimator has an exposure of 35-40 mSv,” she explains.

Giusti says the other benefits of digital radiography are considerable, including the ability to enhance patient education by showing enlarged images, incorporate them into electronic health records, and transmit them electronically to colleagues. “There is also the perception among patients that dental offices that are using current technology may offer the best services,” she adds. 

Patient Selection

The ADA, in collaboration with th ewww.fda.gov FDA, developed guidelines—Guide to Patient Selection for Dental Radiographs—for the prescription of dental radiographic examinations to serve as an adjunct to the dentist’s professional judgment of how to best use diagnostic imaging.6 It stresses the importance of weighing the risks and benefits while using imaging methods, which are so essential in helping the dental practitioner evaluate and definitively diagnose many oral diseases and conditions.

The ADA stood by these guidelines when a controversy arose in April 2012 with the publication in the journal Cancer7 of a study finding 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.8 The ADA said: “The ADA has reviewed the study and notes that the results rely on the individuals’ memories of having dental x-rays taken years earlier,” and that “results of studies that use this design can be unreliable because they are affected by what scientists call ‘recall bias.’”8

The AAOMR, too, responded quickly both to its membership and the journal in which the study was published. On its website it questioned the validity of the study and reinforced the importance of radiography. “Taken together, the methodological weaknesses of this study put the validity of any relationship between dental radiographs and meningioma into serious question. Oral and maxillofacial radiography is an important diagnostic tool in the armamentarium of the dentist, and the American Academy of Oral and Maxillofacial Radiology continues to endorse its careful and judicious use in dentistry.”9 In a Letter to the Editor of Cancer, it said, “We are concerned that patients may draw inappropriate conclusions from this study, and the press coverage it has received, and refuse needed radiographs, unnecessarily compromising their care.”10

The bottom line, as the ADA guideline suggests, is that it’s a judgment call. “The dentist, knowing the patient’s health history and vulnerability to oral disease, is in the best position to make this judgment. For this reason, the guidelines are intended to serve as a resource for the practitioner and are not intended to be standards of care, nor requirements or regulations.”6

That said, Giusti explains, there are standard protocols for managing more vulnerable patients, including children and those who are undergoing radiation therapy, chemotherapy, or are in some other way immunocompromised. Practitioners must assess previous imaging, the effects of medications upon xerostomia, decay rate, and the need to modify standard recommendations of a full-mouth series every 5 years, updated with bitewing x-rays annually. Dentists may prescribe bitewing or periapical imaging more or less frequently depending on a particular patient’s needs.

There are also special considerations needed for pregnant patients, many of whom “self-select” by choosing not to come in at all during their pregnancies. Giusti says her clinic takes precautions when pregnant patients come in for treatment. “We try to avoid any ionizing radiation in the first trimester, unless there’s an emergency or an infection that needs to be dealt with. Then we’ll take the minimal number of x-rays to diagnose the problem.”

In the second trimester, she says they are “more lenient,” although they make every effort to take a minimum number of x-rays that are medically necessary. “Many dentists will do fillings and other elective treatment during the second trimester.” However, she says, most dentists try to avoid treatment that is not medically necessary during the third trimester. “Of course, if the patient is in pain or has an infection, which is also a danger to the unborn baby, we try to solve the problem at hand.” (The ADA website has these patient selection criteria for reference.)

Sometimes, too, patients mention having recently had a mammogram or chest x-ray and elect to forego additional exposure in the dental office, if possible.

One problem in making these judgment calls, says Giusti, is that there’s no recommended ceiling on the amount of medically necessary radiation a person should receive during a given time period. “We can’t recommend that patients skip x-rays that are medically necessary.” The recommended annual dose limit for the general public from the International Commission on Radiological Protection of 1mSV exposures from oral and maxillofacial radiology are usually not even included in calculations of exposures to the population because they are less than 2.5% of the annual exposure resulting from diagnostic radiology, she explains, adding that medical imaging results in far greater exposure to patients. 

How Much Is Too Much?

However, parameters can perhaps be extrapolated from regulations pertaining to occupational exposure. For pregnant dental personnel, the radiation exposure limit reported by The National Council on Radiation Protection and Measurements (NCRP), is 0.5 mSv per month; the total limit for occupational exposure is 50 mSv in 1 year; and an individual’s lifetime occupational effective dose is capped at 10 mSv times the person’s age.11

Conclusion

In truth, the vast majority of radiation received by patients comes not from unnatural sources in the healthcare setting but from natural sources. The NCRP places the effective radiation dose equivalent from all sources in the United States at 3.6 mSv per year, of which 3 mSv is from natural sources. And of that remaining 0.6%—most of which is medically related—only 1% is dental.

According to the ADA’s section on radiation exposure,11 radiation exposure associated with dentistry represents a mere 0.2% of total exposure from all sources. Nevertheless, dentists should continue to make every effort to minimize their patients’ radiation exposure.

References

1. American Nuclear Society. Radiation Dose Chart. Available at: http://www.new.ans.org/pi/resources/dosechart/msv.php. Accessed November 7, 2012.

2. ADA Statement: Diagnostic Radiation Procedures Must Be Used Sparingly to Reduce Dental Radiation Risk. November 23, 2010. Available at: http://www.ada.org/5081.aspx. Accessed November 7, 2012.

3. American Dental Association Council on Scientific Affairs. The Use of Dental Radiographs: Update and Recommendations. Available at: http://www.ada.org/sections/professionalResources/pdfs/report_radiography.pdf. Accessed November 8, 2012.

4. Food and Drug Administration. Dental Radiography: Doses and Film Speed. Available at: http://www.fda.gov/radiation-emittingproducts/radiationsafety/nationwideevaluationofx-raytrendsnext/ucm116524.htm. Accessed November 8, 2012

5. Frederiksen NL. X rays: what is the risk? Tex Dent J. 1995;112(2):68-72. 

6. American Dental Association. Oral Health Topics: Guide to Patient Selection for Dental Radiographs. Available at: http://www.ada.org/2760.aspx#safety. Accessed November 8, 2012.

7. Claus EB, Calvocoressi L, Bondy ML, et al. Dental x-rays and risk of meningioma. Cancer. 2012;118(18):4530-4537.

8. Williams J. Experts question x-ray study. ADA News. April 13, 2012. Available at: http://www.ada.org/news/6979.aspx. Accessed: November 12, 2012.

9. The American Academy of Oral and Maxillofacial Radiology. AAOMR Response to Recent Study on Dental X-ray Risks. Available at: http://c.ymcdn.com/sites/www.aaomr.org/resource/resmgr/docs/aaomr_response_to_study2.pdf. Accessed November 12, 2012.

10. Letter to the Editor of Cancer. Available at: www.aaomr.org/resource/resmgr/docs/letter_to_the_editor_of_canc.pdf Accessed: November 12, 2012.

11. American Dental Association. Oral Health Topics: Radiation Exposure. Available at: http://www.ada.org/2760.aspx#safety. Accessed November 8, 2012.


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