Dental X-Rays: Worth the Risk?

I've had two dental X-rays in my life, both times as an adult because I was in pain. My mom never let my brothers and me get dental X-rays when we were kids because she was concerned about potential health effects. My mom told me recently that her misgivings came from working with dental students many years ago; they told her that the only thing dental X-rays were good for was paying for the X-ray machine. 

My son had his first dental appointment over the summer and the dental assistant told me they would be doing bitewing X-rays on my son. I told her that I didn't want him to have them and explained that I wasn't comfortable with their safety. She responded by saying, "An X-ray has less radiation than a microwave. Do you use a microwave?" "Not on my head," I told her. We left it at that.

Benefits of Dental X-Rays

A dental X-ray provides your dentist with a picture of the hard and soft tissues of the mouth. While at least one study shows that findings on clinical exam alone agree with findings on dental X-rays over 90% of the time (in other words, your dentist can usually see problems just by looking in your mouth and examining it); there are times when X-rays help to diagnose issues not always visible to the naked eye such as: 

• Cavities between teeth or under fillings
• Diseases in the bone
• Gum disease and infection
• Tumors

Professional Guidelines

The American Dental Association (ADA) says that radiation exposure from dental X-rays represents a "minor contribution" to a person's total exposure from all sources. But the group does recognize that dental X-rays are not without risk and that the effects accumulate over time. Furthermore, the group recommends that dentists should perform an examination and use their clinical judgement before making the decision to get an X-ray. Here is an excerpt from the guidelines, and you can read the full booklet entitled Dental Radiographic Examinations: Recommendations for Patient Selection and Limiting Radiation here.

Source: ADA

Though the ADA does not regulate dental x-rays, they do make recommendations regarding how often a patient should have them done, based on age and dental history. In general, dentists are expected to follow the "ALARA" principle when performing X-rays: ALARA stands for "as low as reasonably achievable."  

• For low risk-patients:

• Adults should have bitewing X-rays every 2 to 3 years.

• Teens should have bitewing X-rays every 1½ to 3 years.

• Children should have bitewing X-rays every 1 to 2 years.

• For people who have tooth decay or are at high risk of getting cavities:

• Adults should have bitewing X-rays every 6 months to 1½ years.

• Children and teens should have bitewing X-rays every 6 to 12 months.

Source: Dimensions of Dental Hygiene, reprinted from ADA

Radiation Exposure in Humans

There are two types of radiation: "non-ionizing" radiation such as sound waves, visible light, and microwaves; and "ionizing radiation," which is the type people typically think of when they refer to radiation. Non-ionizing radiation uses include electric power generation, lasers, and manufacturing processes.

During an X-ray, an X-ray machine sends this radiation through the body. Some of the radiation emerges on the other side of the body, where it exposes film or is absorbed by a digital detector to create an image. And some of it is absorbed in body tissues. It is the radiation absorbed by the body that contributes to the "radiation dose" a patient accumulates.

In the US, the unit of measurement for a radiation dose is the rem (Roentgen Equivalent Man); doses are most commonly reported in millirem (mrem). (Most other countries use the metric "milliSievert" unit of measurement.) According to the National Council on Radiation Protection and Measurement, the average annual radiation dose per person in the US is 620 millirem (6.2 milliSieverts).

Radiation exposures come from natural and man-made sources. Radiation dose per person from medical X-rays has increased almost 500 percent since 1982, from 11% to around 35-36%.

Source: US Nuclear Regulatory Commission

General Health Effects of Radiation

According to the EPA, "there is no firm basis for setting a 'safe' level of exposure" to radiation. Children are at a particular risk for effects from ionizing radiation because their cells are rapidly dividing and there is more opportunity for radiation to disrupt the process. In setting limits, EPA "makes the conservative assumption that any increase in radiation exposure is accompanied by an increased risk of effects."

Long-term, low-level exposure to radiation is known to cause cancer, birth defects, and genetic mutations (those last two are the reason that a female patient is always asked if she is pregnant before an X-ray is administered). (Acute high-level exposures like those experienced by Chernobyl victims carry a whole other set of serious health effects like internal bleeding, nervous system damage, and even death; these are not relevant to this topic.)

Types of Dental X-Rays

There are quite a few different types of dental X-rays used for different things. 

• Bitewing X-rays are taken with the patient biting down on film. Bitewing X-rays are used to detect decay between teeth and changes in bone density caused by gum disease, to determine the fit of dental crowns or restorations, and to inspect integrity of tooth fillings.

• Periapical (limited) X-rays show the whole tooth from the crown to beyond the root tips to the supporting bone in one area of either the upper or lower jaw. These X-rays aid in treating conditions such as periodontitis, advanced gum disease, and detecting abscess.

• Panoramic (Panorex) X-rays require a machine that rotates around the head and show the entire mouth in one image. Panoramic X-rays are used to plan treatment for dental implants, detect impacted wisdom teeth and jaw problems, and diagnose bony tumors and cysts. 

• Multi-slice computed tomography (MCT) shows a particular layer or "slice" of the mouth while blurring all other layers. This type of X-ray is useful for examining structures that are difficult to see clearly.

• Cephalometric projections, which show the entire head, help examine teeth in relation to a patient's jaw and profile. Orthodontists use cephalometric projections to develop their treatment plans.

• Sialography uses a dye injected into the salivary glands to visualize them on the X-ray film. A sialography typically is used to identify salivary gland problems, such as blockages or other problems.

• Cone beam CT scanners show the body's interior structures as a three-dimensional image. CBCT — often performed in a hospital or imaging center, but increasingly being used in the dental office — is used to identify facial bone problems, such as tumors or fractures. CT scans also are used to evaluate bone for dental implant placement and difficult tooth extractions to avoid possible complications during and after surgical procedures.

As you might expect, different types of X-rays come with different levels of radiation exposure. Below is a chart that details exposures from some types of dental x-rays, and compares the exposure to other common sources of radiation. Amounts of radiation received from dental X-rays is relatively low.

Source: Dear Doctor, Inc.

Dental X-Rays & Cancer Risk

Dental X-rays are the most common way Americans are exposed to radiation. But there is surprisingly little research on the effects of dental X-rays on humans. As noted above, children are particularly susceptible to radiation's effects. The Society for Pediatric Radiology reports that children are at an approximately 3 to 5 times higher radiation-induced cancer mortality risk than adults.  

Some studies have shown a relationship between dental X-rays and cancer. While more research is needed, the findings below suggest that patients and dentists should carefully consider the potential risks of exposing patients to radiation. 

Thyroid Cancer: 

A 2013 study in the journal Clinical Thyroidology found that repeated dental X-rays without a neck shield were associated with all types of thyroid cancer.

A 2010 study reported that men and women who had four or more dental X-rays had twice the risk of thyroid cancer; and those who had ten or more X-rays had 5.4 times the risk.

Salivary Gland Cancer:

Cancers of the salivary gland (parotid gland) have also been linked to dental X-rays, according to this National Cancer Institute publication. 

Brain Cancer:

A 2012 study published in the journal Cancer  made a lot of headlines when it found a possible relationship between dental x-rays and a certain type of brain cancer called a meningioma. In the study, researchers surveyed 1433 meningioma patients and 1350 healthy patients. The meningioma group was twice as likely as the control group to report ever having had a bitewing exam and more likely to report having had a panorex exam at a young age (under 10 years old) or on a yearly or more frequent basis. Though most meningioma tumors are benign (non-cancerous) and tend to grow slowly, some cause significant symptoms such as seizures, vision changes, hearing loss, weakness, and even death.

This study has been criticized due to certain limitations of the study, including the fact the reports were based on patient's memories, rather than on dental records. In addition, X-rays used today deliver less radiation than they did when the subjects of this study received them, so the results may not apply to today's patients. 

What You Can Do

Some people are at a higher risk of dental disease than others. You should understand your risk (and your child's risk) and ensure that your dentist follows the ALARA principle (as low as reasonably achievable) when administering X-rays. Some steps you can take:

• Make sure the dentist (not the assistant) performs a clinical exam before administering any X-rays. (Though apparently some dental professions feel that patients should get X-rays right away and that "it is best not to ask the patient's permission.")

• Always ask why the dentist is doing the X-ray. (And keep in mind the answer "because your insurance covers it" is NOT a good reason!)

• Be aware that some types of dental X-rays exposure you or your child to more radiation than others. Newer machines called cone-beam CT scanners are particularly high in radiation and should be avoided, according to some experts. And digital images expose people to less radiation. 

• Insist on a thyroid protector.

• Keep in mind that radiation exposure is cumulative (adds up over time with repeated exposures).

Final Thoughts

The relative lack of research on health effects means that I'll avoid dental X-rays for my son and for me, unless there is a really good reason to do them. And while I can't argue with the premise that an X-ray may turn up a hidden problem, the overall logic seems flawed to me. There are plenty of health problems that could be found with a scan if you went looking for it, but to me the potential risks associated with getting an X-ray "just in case" outweigh the benefits.

Some dentists tell you that they simply must do dental X-rays, because they could be sued for malpractice if they are not performed and a problem turns up later. I am unable to confirm or deny the truth of this claim, but I'd gladly sign a waiver absolving them from litigation. Some dentists even refuse to treat people who refuse X-rays, though I've never experienced this. 

And what about the two issues we started with? Do dentists perform unnecessary procedures for profit? Well, some do and some don't. There are no figures available that I could find, but I'm sure that for every horrifying case like this or fraudulent dentist like this, there are many more who are simply trying to give their patients the best care possible. 

And is my use of a microwave worse than a dental X-ray? It's apples and oranges, according to this article: these two things emit different types of radiation.