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Are Dental X-rays Risky Business?

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drmithila's picture
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Address you patients' concerns....Are they necessary? Yes. Are they safe? They can be safer

Well, it’s official - Dr. Oz has spoken! On September 28, 2010 this well-known physician suggested the use of thyroid collars and protective leaded aprons to reduce a patient's x-ray exposure to the thyroid gland. Actually, the statement was both appropriate and timely. It has caused tremendous discussion among both medical and dental professions and among consumers.

Rectangular collimation

Interestingly, as pointed out in the “Issues Alert” bulletin from the American Dental Association on April 6, 2011, the ADA already “strongly recommends” this strategy for “children, women of childbearing age and pregnant women who are especially susceptible to radiation effects”. This position is also endorsed by the AAOMR (American Academy of Oral and Maxillofacial Radiology). Not only has our radiology specialty been saying this for years, but we've been teaching this for over 30 years in all North American dental schools. Why then, is there such resistance to the adoption of “rectangular collimation”? Well, my colleagues, it’s like the comic strip character Pogo said:

“We have met the enemy and he is us”.

Most dentists are convinced (as well as some dental auxiliaries) that, because of their experience and dental schools, you cannot “hit” the x-ray receptor target - whether film phosphor plate or solid state detector - with anything less than a large round cone. This is not only false, but silly as well...because there is technology available today that allows the easy adoption of rectangular collimation for use on all existing dental x-ray tube heads.

By retrofitting an existing x-ray generator with one such device called Tru-Align, you can reduce excess surface radiation to the patient by as much as 98%. And, you can do this without much fuss, training or expense. The diagram below illustrates the use of a rectangular collimation device which is only 2% larger than the actual image receptor.

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drmithila's picture
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Are Dental X-rays Risky Business?

By fixing the receptor to the rectangular collimator, almost all “retakes” due to missing the image receptor are eliminated—easily and effectively. In addition, linking the receptor to the dental x-ray tube head forces perfect parallelism. This results in the elimination of any missionaries and distortion (which also reduce image quality and can lead to additional “retakes”).

In the RSNA (Radiology Society of North America), teaching files -as posted by the State University of New York - collimation of the x-ray beam to the receptor is beneficial to the patient and the clinician because:

“X-ray beam collimation for radiography and fluoroscopy projection imaging is important for patient dose and image quality reasons. Actively collimating to the volume of interest reduces the overall integral dose to the patient and thus minimizes the radiation risk. Less volume irradiated will result in less x-ray scatter incident on the detector. This results in improved subject contrast and image quality.”2

To summarize then, rectangular collimation of any "flavor":

reduces patient dose
reduces or eliminates retakes
cleans up scatter to the receptor, thus
improving image quality
Does anyone see a downside to the adoption of rectangular collimation?

Are dental X-rays safe?
The short answer is “Yes”, but not absolutely. Any x-ray exposure carries with it some risk. All medical and dental professionals should weigh the benefits of an x-ray procedure, no matter what the modality, against the risk of x-ray exposure dose to the patient. This too, we’ve been teaching for decades. As low as our dental x-ray doses to the patient are, the risk of inducing a cancer in a patient is cited as "one in 1 million". The citation however, is for one FMX (full mouth x-ray) series or CMS (complete mouth series), most often 18 to 20 images, taken with conventional dental x-ray films.

Many in our profession have moved beyond film as their primary dental x-ray receptor. Unfortunately, not all professionals have moved to solid state detector imaging. Even those who have adopted phosphor plate technology, use exposure times which are less than film but still much greater than CCD or CMOS receptors. So, as a profession we have moved towards the fastest receptors possible eliminating much of the x-ray dose. However, most of our profession has not adopted the rectangular collimation for use with these faster receptors. This is like buying a Lamborghini with a two-stroke "Smart Car" engine. We haven’t gone far enough because we can’t go fast enough.

The dose from a digital intraoral receptor is about 0.005 mSv. This is very low. By comparison, a chest film is 0.1 mSv and a CT examination of the chest is 7.0 mSv. Mammography at 0.4 mSv is considered “very low”, the equivalent of 7 weeks of background radiation - estimated at 3.0mSv/year3. So our profession is doing very well!

However, we dentists perform multiple x-ray procedures at multiple times over a patient’s lifetime. And, although x-ray dose itself is not cumulative, any damaging effects suffered at the time of exposure are. We must do our best to reduce our x-ray exposure doses to our patients to as little as possible. This is the concept behind the “Selection Criteria”4 developed by both the FDA and members of our profession. These selection criteria give us recommendations for the number, type and frequency of our x-ray procedures for patients. They are based on a thorough examination and history of our patient PRIOR to ordering any diagnostic test referred to as an “x-ray”.

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Are Dental X-rays Risky Business?

Are dental X-rays necessary?

No prudent dental clinician would consider performing a surgical procedure, something as simple as a cavity preparation, without x-ray information to help them characterize the disease process and make an informed clinical decision. In most cases, our profession does a good job of determining what dental, panoramic, and now even cone beam x-ray procedures are necessary for patients. Again, these selection criteria published by the FDA, the ADA and our radiology specialty in several journal publications are available to give the clinician guidelines for the safe use of x-ray radiation. The first publication of these selection criteria was actually in the Journal of the American Dental Association in 1988. However, like collimation, these guidelines have largely been ignored.

So yes, most dental x-rays performed by our profession are necessary. What we need to do better is use the publish selection criteria for ordering our images and use the most contemporary radiologic devices such as solid-state detectors and x-ray collimation to ensure that we move forward in step with the concept of ALARA - As Low As Reasonably Achievable. Rectangular collimation, although a seemingly small step will indeed result in a huge reduction of x-ray exposure dose to the patient. Now that it has been made simple, economical and widely available, there is simply no valid reason for not employing it in our dental practices. The ADA, the FDA and many specialty organizations in dentistry recommend it. Our patients will begin to demand it, especially in light of all the recent concerns raised in the journalistic media.

Why not jump on the bandwagon now, accept the inevitable, and "do the right thing" in your practice? You can even market your new "radiation hygiene" to your patients, on your website and in your marketing materials.

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Are Dental X-rays Risky Business?

The Bottom Line

Now that I have made the argument based on reduction of patient x-ray dose by the use of selection criteria and the rectangular collimation, let’s make the argument based on ROI (return on investment). For the radiologist reading this article, yes I know, ROI in our paradigm means “region of interest”. But for clinical colleagues these two uses of the acronym ROI are not mutually exclusive - nor should it be.

Dentists delegate x-ray procedures for almost all patients that walk through the doors of their office. New patient examinations, re-care examinations, orthodontic examinations emergency examinations, growth and development examinations, pain evaluation, TMJ evaluation, paranasal sinus evaluation, airway analysis, and pre-surgical evaluation of third molars for possible extraction are just some of the ways that dentists and dental specialists must evaluate their patients. I’m a radiologist. I am not saying take these x-ray examinations to make money. IT JUST HAPPENS! The x-ray procedure has the biggest “margin” of any procedure performed in the dental office. You don’t do a crown every day or an implant, but you do order radiographs!

Even with the use of selection criteria to minimize the number of x-rays taken, the average clinician will generate substantial revenue from their x-ray procedures. If you don’t believe me just use your practice management software for producing a “productivity report”. Instead of generating a generic report, only query your software for productivity related to the procedures for radiographs - all the CDT codes in the “2” series. If you run this report for six months you will be shocked to see the income generated. Your shock will be translated into the absolute need to purchase and use the best equipment available, the fastest receptors available, and will justify your move to a total digital x-ray environment. Clinicians who I have directed to perform this procedure has been both rewarded and motivated to contemporize their x-ray procedures and devices. Those who have been resistant to leaving film behind have happily made the move and suffered no regret.

Summary

Compared to daily risks we take, x-rays are safe. After clinical and historical examination of the patient the majority of x-rays are necessary. The clinician must take all steps possible to reduce x-ray exposure dose to his or her patient. Selection criteria and contemporary devices such as the ones that incorporate rectangular collimation, simply an economically are the best way to improve your practice, allay your patients’ fears and doubts about x-ray exposures and increase the “bottom line” of your practice. Again, where's the downside? And, what are you waiting for?

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Are Dental X-rays Risky Business?

Skin Burns

As discussed in the introduction, the principal hazard associated with use of analytical x-ray equipment is localized skin burns following exposure to the primary beam.

Experience with exposure of relatively large areas of skin to radiation has shown that it requires doses of approximately 300 rad (3 gray) to produce a visible reddening of the skin.
Doses of approximately 1500 rad (15 gray) are required in order to produce serious burns with blistering.
When doses reach 3000 rad (30 gray) very serious burns requiring skin grafts or amputation may result.
The bum symptoms may require from
one to several weeks to develop, depending on the dose.

Burns Produced by X-Rays
Description of Tissue Damage Approximate Dose Required (gray)
Perceptible reddening of skin 3
Dry desquamation of skin 10
Wet desquamation and blistering 15
Ulceration and necrosis of skin 30

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Are Dental X-rays Risky Business?

Analytical x-ray equipment makes use of very narrow collimated x-ray beams of high intensity. Exposure of the eyes or the skin of the body to the primary x-ray beam may result in severe radiation burns in a matter of seconds. These burns heal poorly, and on rare occasions have required amputation of fingers.

Localized radiation burns produced by the high intensity primary x-ray beam is the principal hazard associated with the use of analytical x-ray equipment.
Scattered Radiation

A hazard may also exist from exposure to scattered radiation. Scattered radiation is produced when the primary beam strikes collimators, samples, beam stops or shielding. The intensity of the scattered radiation is a couple of orders of magnitude less than that of the primary beam. It is possible for these scattered radiation fields to result in exposures, which exceed regulatory limits, however.

Scattered Radiation may exceed regulatory exposure limits.
Hazards Associated with X-Ray Exposure

The hazards most often associated with exposure to x-ray radiation include increased risk of cancer and increased risk of genetic effects in exposed populations. These effects are effectively discussed in a number of readily available publications and will not be elaborated upon in this document. NRC Regulatory Guides 8.29, entitled Instruction Concerning Risks from Occupational Radiation Exposure, and 3.13, entitled Instruction Concerning Prenatal Radiation Exposure

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Are Dental X-rays Risky Business?

A growing body of evidence suggests that radiographs used in dental and medical practices can induce cytotoxic effects in the exposed tissue at the cellular level and damage DNA.Researchers from the Maharishi Markandeshwar College of Dental Sciences and Research in India used a micronucleus assay test to assess chromosomal damage in the buccal mucosa and maxillary anterior gingiva,

"In the past, various biomarkers assessing metaphase chromosomal aberrations, sister chromatid exchanges, and host cell reactivation have been used to determine the effect of ionizing radiation," the study authors wrote. "However, these methods were typically laborious and time-consuming or required a high level of expertise to accurately interpret the slides."

Micronucleus assays can be used to assess chromosomal damage and are commonly examined in routine cytopathologic preparations, the researchers added. In addition, micronucleus assay tests are simple, rapid, and do not require much expertise.

Statistically significant increase

For this study, the researchers analyzed the panoramic radiographs of 80 patients in two groups: Group 1 included 20 males and 20 females, ages 15-25 years; group 2 included 20 males and 20 females, ages 40-50 years. All radiographs were taken using an Orthophos XG 5 DS Ceph (Sirona Dental Systems) with these parameters: 64 kV, 8 mA, 14.1 seconds.

The mucosal samples were taken from the buccal mucosa and gingiva using a wooden spatula immediately before radiographic exposure and 10 days after exposure. For each subject, a minimum of 500 cells each from the gingiva and buccal mucosa were studied using blind analysis, for a total of 1,000 cells for each individual, both pre- and postexposure, at 1,000x magnification.

The researchers found a statistically significant increase in the micronucleus count of the gingival epithelial cells after radiographic exposure: 1.08 before and 1.6 after (p < 0.05). They also found an increase in the postexposure micronucleus count in the buccal mucosa, although it was not statistically significant (p > 0.05). Age also appeared to be a factor, they reported, suggesting that micronucleus frequency increases with age.

"Epithelial cells are easy to obtain and appear to be target cells for this particular x-ray exposure," they wrote. "The higher micronucleus frequency in epithelial cells obtained from the gingival can be explained by the direct exposure of gingival epithelium to x-rays since the radiation from panoramic radiography is directly absorbed by gingival cells."

The researchers suggest a need for larger epidemiologic studies to precisely quantify the risk of these effects, but also caution that radiographs should be taken with adequate protection measures and only when the potential benefit outweighs the potential risk.

"Although radiation-related effects from panoramic radiography are reduced compared with full-mouth intraoral periapical radiographs or radiotherapy, the results of this study show that genotoxic effects do take place," they concluded.

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Are Dental X-rays Risky Business?

Dentists have been warned against using a hand-held X-ray machine on patients as it poses a significant health risk.

The cheap imported machine, known as the Tianjie Dental Falcon, exposes users and patients to 10 times the normal level of radiation, increasing their risks of cancer and organ damage.

The Medicines and Healthcare Regulatory Agency is asking NHS and private dentists to dispose of these devices.

It is not known how many patients may have been put at risk.

So far, 13 of the machines - sold on internet sites including eBay by a Chinese manufacturer - have been seized at a distribution centre.
At least one dental surgery has been found using the device.

Dangerous
Emergency testing of the product by the Health Protection Agency and scientists at King's College Hospital in London revealed that it has insufficient lead shielding inside it to protect dentists and patients from excessive radiation.

The machine's X-ray beam is also too wide, which means a patient's whole skull and brain is exposed to radiation rather than just their mouth.

And the device poses an electrical hazard because it comes with a European plug and a travel adapter that are not earthed or fused for the UK mains supply. As well as being a fire hazard, it could cause a serious electric shock (50,000 volts) to the dentist or patients.

Scientist Donald Emerton, who tested the device, said: "Over time someone operating this machine, such as a dental assistant, would be exposed to unacceptable levels of accumulated radiation and this would have an increased risk to their health.

"I certainly wouldn't want someone to use this piece of equipment to take an X-ray of me."

The MHRA believes it has shut down the UK's only distributor but says investigations are ongoing to ensure no more can be sold and used here. The problem first came to light in June 2012.

The manufacturer - Zhengzhou Tianjie Electronic Equipment Co - is currently unavailable to contact.

The Tianjie Dental Falcon was priced at about £200, a fraction of the cost of other dental hand-held X-ray sets available for sale in the UK, which can be over £4,000.

Bruce Petrie, of the MHRA's Medical Devices Enforcement Team, said: "It's vital that dentists and dental staff do not buy these dental X-ray machines from eBay or other websites because they are not approved and not safe for dentists or patients.

"We are working with eBay and other governments to ensure dentists and patients are protected."
Barry Cockcroft, chief dental officer for England said: "It is vitally important that when buying equipment, dentists make sure it is appropriate and safe for use.

"I would urge all dental professionals to be cautious of seemingly cheap devices which may not be fit for purpose and potentially dangerous."

Richard Paynter, deputy director of the Health Protection Agency's Centre for Radiation, Chemical and Environmental Hazards, said: "We're delighted that MHRA is now taking such positive steps to ensure public and occupational protection from unnecessary radiation exposure.

 

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