X-rays of our teeth are routinely prescribed by dentists, but you know what else follows a certain periodicity? Media coverage of the alleged danger and overuse of these dental radiographs.
In 2012, we were scared into thinking thatĚý, a cancer of the thin membranes that wrap up our brain and spinal cord. It didn’t matter, as was pointed out by Drs. Hendry and Ritchey forĚý, that theĚýĚý°ů±đ±ôľ±±đ»ĺĚýentirelyĚýon people remembering how many dental X-rays they had had since childhood and which kind (a near-impossible feat if we’re aiming for accuracy), and that the association with meningioma was simply not there when looking at full-mouth radiographs, which deliver a much higher dose of radiation. “Fear sells,” the dentists pointed out, “and the media loves it.”
Four years later, a health economist wrote a piece forĚýĚýdecrying the overuse of X-rays in dental practice. “When dentists take bitewings at routine visits, they may be doubling their revenue,” he remarked.
This year, it’s anĚýĚýpiece provocatively titled, “Routine dental X-rays are not backed by evidence—experts want it to stop.”
Do we need that periodic dose of radiation in the dentist’s chair or should we learn to say no to protect our health and wallet?
An appetite for better dataĚý
Dental radiography is common: the U.S. National Council on Radiation Protection and Measurements estimated atĚýĚýthe number of such procedures done in the United States in 2016, which wasĚýĚýwith the number of people living in the U.S. that year.
The most common radiography taken at the dentist’s office is known as a bitewing X-ray. A T-shaped piece of film or (more commonly now) a digital sensor (called a “wing”) is inserted in the mouth and you “bite” down on it before the X-ray is taken. Bitewing X-rays will show the crowns of the top and bottom teeth on a single image.
Other types of dental radiographic procedures can be done, involving higher levels of radiation, such as a full-mouth series (consisting of 18 separate images in adults and 12 images in children) and even a type of CT scan called cone-beam computed tomography.
Bitewing X-rays are often done every six months, and some researchers have questioned the benefits of this schedule. For example, a Brazilian group conducted aĚýĚýa few years ago to see if the detection of dental caries in preschool children was really helped by the use of X-rays. It turns out that the decisions the dentists made after simply inspecting the mouth of the child with their own eyes were typicallyĚýnot changedĚýby the use of an X-ray. In fact, when the X-ray contradicted the visual inspection by the dentist, it tended to give a false negative, meaning that the X-ray was interpreted as “no caries” when visual inspection had revealed an early lesion.
(It’s important to point out that this analysis was not part of the initial trial and was designed after the study had been conducted. These types of “secondary analyses” need to be reproduced in studies designed for them, since you can always torture a data set long enough to get a positive result out of it by chance alone.)
When the Cochrane Collaboration, which specializes in synthesizing the evidence we have for medical interventions, looked at studies of how X-rays could influence the detection of early dental caries, the result wasĚý. X-rays seemed to miss caries sometimes, but the studies themselves were rarely done in human patients (instead, they were carried out in already extracted teeth) and the quality of the evidence was low. I don’t think we can say that dental X-rays are useless or harmful, though, because the scientific research done so far is simply subpar.
For a bit of context, the concept of evidence-based medicine is relatively new, acquiring its name inĚý. Before that, treatments were adopted based on our growing understanding of the human body, and a prominent doctor proclaiming that it worked with his patients was enough to make it a mainstay. Evidence-based medicine challenged this by inviting healthcare professionals to consider the weight of the evidence and by teaching them that not all studies are created equal. Adoption should not be sustained by tradition but triggered by rigorous experimentation and questioned when better evidence is published. Randomized clinical trials became more popular and the body of evidence was arrived at with the use of systematic reviews and meta-analyses of the available data.
But other health disciplines have lagged behind, including dentistry. Many write-ups in the dentistry literature on the subject of X-rays conclude that more studies are needed, and this time it’s not just a token line. Good data is hard to come by.
So, what is a dentist to do in the meantime?
It’s the dose that makes the poison
I reached out to a number of dental associations, which all agreed in saying that it is up to the dentist to use their professional judgment as to how often X-rays are needed. As the Canadian Dental Association mentioned to me via email, “compliance with our recommendations is always voluntary” since it is not a regulatory body. ItsĚýĚýhighlights the need for the dentist to examine the patient first as opposed to automatically going for the X-rays. The Royal College of Dental Surgeons of OntarioĚýĚýon this point as well. This has not been my experience, however. X-rays are alwaysĚýthe very first thingĚýdone to me during a routine dental checkup.
The American Dental Association, in itsĚý, goes more in-depth with its recommendations. For a returning patient with no caries and no increased risk for developing them, the ADA recommends a delay of one to two years between bitewing X-rays for children; a year and a half to three years for teenagers; and two to three years in adults. For children and adolescents at an increased risk for caries, the interval is reduced to between six months and a year, and for adults, to between six months and a year and a half.
All this focus on dental caries, though, can make us forget that dental X-rays are not only used to prevent cavities. They can be indicated to monitor gum disease, to investigate swelling, bleeding or unexplained tooth sensitivity, and to examine the impact of trauma to the face and teeth. The timing of dental X-rays is thus not a one-size-fits-all situation. Dentists need to consider a patient’s oral health, their age, their risk for disease, and any symptom being reported. “Radiographs should not be taken simply because a specific period has elapsed since the last radiographic examination,” the Canadian Dental Association wrote to me, a sentiment which is echoed on theĚýĚýof the Royal College of Dental Surgeons of Ontario: “A decision about radiographs should never be based on inflexible time periods alone, such as bitewing radiographs every six months.”
But if dentistsĚýdoĚýoveruse X-rays, or are simply too quick to rely on the six-month rule, are we as patients being harmed? X-rays are a type of ionizing radiation, which is known to mutate our DNA, and too much of this radiation can cause cancer. The dose we absorb from bitewing X-rays, however, is really, really, really small. A single bitewing X-ray, done using a digital instrument and not a film that needs to be developed, is on the order ofĚýĚýtoĚýĚýmicroSieverts (µSv). The Sievert is a unit measuring how much radiation a part of your body has effectively received. This is different from the dose delivered by the machine; Sieverts take into account the fact that different parts of the body absorb radiation differently.
We usually speak of microSieverts or milliSieverts when it comes to radiation affecting humans, and there are 1,000 microSieverts (µSv) in a milliSievert (mSv). I will stick to microSieverts for consistency. Getting back to our bitewing X-rays, a chest X-ray by comparison will deliver a dose ofĚýµ, meaning two orders of magnitude greater than a bitewing X-ray. A CT scan of the head is aboutĚýµ. An effective dose ofĚýµĚýis where people start to show symptoms of radiation poisoning.
Still worried about that dental X-ray? Flying from one coast of the United States to the other will expose you toĚýµ, so a round-trip irradiates your body with the equivalent of at least a dozen bitewing X-rays. Afraid of flying? The United States Nuclear Regulatory Commission would like to remind you the average person in the United States receives roughlyĚýµ, half from natural background radiation (meaning cosmic radiation entering our atmosphere and radioactive materials found in the Earth) and half from artificial sources, including medical imagery. Even if you remove these artificial sources, that’s an average of 8.5ĚýµSv per day in background radiation compared to the 0.3 to 5ĚýµSv from that bitewing X-ray. I hope the comparison helps contextualize the numbers we’re dealing with. Even if you assume that all ionizing radiation exposure adds up over a lifetime (and there isĚýĚýon this point), we are talking incredibly tiny numbers.
The radiation dose we get at the dentist’s is so low nowadays that the popular lead apron is not even needed anymore. I reached out to Dr. Grant Ritchey, a dentist in Kansas, who confirmed. “We still use them,” he wrote to me, “because I think it makes patients feel safe. It’s mainly theatre though, in my opinion.” Same response from Dr. Mark Grossman, a dentist who has written for our Office before: he still uses them because there is no harm done and it may make the patient feel more comfortable.
Dental personnel doing multiple X-rays a day are obviously at greater risk, but a back-of-the-envelope calculation reveals that the risk is far from catastrophic. Let’s use the highest effective dose for a bitewing X-ray, 5ĚýµSv, and assume two bitewings per patient. Let’s also do something reckless: our imaginary dentist will be receiving the exact same effective dose as the patient when taking the X-ray, which is simply not the case. And let’s imagine that they do this to eight patient every day, five days a week, 52 weeks a year. They would be receiving an effective dose of 20,800 µSv annually. To this we add background radiation and exposure to artificial sources of radiation, 6,200ĚýµSv, and our dentist ends up with 27,000ĚýµSv yearly.
This is still well under theĚýµĚýmaximum permissible annual dose of ionizing radiation for healthcare workers according to the American Dental Association. Yes, other types of radiographic imagery will delivery higher doses of radiation, but our dentist is not absorbing anywhere near the dose the patient is getting. Even when we crank the dials up to ridiculous levels in our theoretical scenario, the irradiation is not calamitous.
Before we accuse dentists of being trigger-happy with their X-ray machine, I should point out a concept that is taught to anyone that will administer X-rays in a clinical setting: the ALARA principle. It stands for “As Low As Reasonably Achievable,” and it means that dentists and doctors must minimize their patients’ exposure to radiation. The idea behind this principle (and other similar ones, like “So Far As Is Reasonably Practicable”) dates back toĚý, so this is hardly new, and it was specifically quoted to me by the Canadian Dental Association in their response to my query.
So, what are we left with? There’s the financial argument. Some dentists may be taking more X-rays than needed in order to charge more. If you do not have insurance and the fee for these radiographs is coming out of your pocket, you may want to ask your dentist why they think they are needed so soon and why they haven’t asked you to open your mouth first. If you do have insurance, the personal cost is lessened but of course the global burden of overprescribed procedures does have an impact on premiums.
Apart from the economic harm, I don’t see how bitewing X-rays every six months is going to increase radiation damage to the body versus every two to three years. The dose borders on being trivial.
It may very well be that dentists overuse them and it is possible that they lead to too many false negative results, but the only way we will know that for sure will be to fund well-designed randomized clinical trials.
It may be time for dentists to open wide and get a strong dose of evidence-based medicine.
Take-home message:
- Bitewing X-rays are the radiographs taken when you bite on a T-shaped sensor at the dentist’s office
- While some studies report that dentists relying on them too much will miss early cavities, the quality of the body of evidence is too low to conclude anything yet
- Even if bitewing X-rays are done too often, the dose of radiation is trivial compared to what we are exposed to every day from cosmic radiation and radioactive material in the Earth
Note: when the article was initially uploaded to the website, the Greek letter mu used to indicate "micro" was accidentally converted into an "m," making "microSieverts" and "milliSieverts" indistinguishable. The article has now been corrected.
