Are Dental X-rays Risky Business?

[drmithila]

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”.