Dental-Patient Issues

I had a dental x ray while I was pregnant. I am worried that my unborn child might have been exposed to the radiation. Can you please tell me if there are any risks to my baby from this?

There is no information suggesting any risk to an unborn child from dental x rays received by the mother. When a pregnant patient undergoes a complete dental x-ray examination, the radiation dose to the fetus is insignificant. And, by the way, it does not matter whether a lead apron was used or not.

Is there anything like a computerized tomography (CT) scan for teeth?

A couple of years ago, a dental CT scan was introduced into this country. There are only a few machines in use, mainly in California, and the one that I am aware of is at the University of North Carolina. There are some ultra-high-resolution dental CT units that are being developed in Japan, but they are not yet licensed for sale in the United States.

I am concerned about a crown put on my tooth in about 1992. I read some information that at one time uranium was added to the porcelain in dental crowns. What are the risks if there is uranium in my crown?

It is true that very small amounts of uranium were added to dental porcelain from the early 1900s through the 1970s. However, according to the Center for Devices and Radiological Health, U.S. Food and Drug Administration, the last of the U.S. manufacturers of dental porcelain phased out the use of uranium in the early 1980s. The original reason for adding uranium in the first place was to make the ceramic look more natural by increasing the fluorescence. However, other materials have been found that work even better and thus the use of uranium was voluntarily withdrawn, even before the new regulations took place. Thus it is highly unlikely that your crown contains any added radioactive material.

Is there residual radiation in a room after a dental radiograph has been taken?

X rays cease to exist when the machine is switched off, much like the light from a light bulb when it is turned off. No residual radiation remains.

How much has dental x radiation been studied and how concerned should I be about having dental x rays done? Is there a limit on how many I can have?

We now have very complete information on patient radiation doses from dental x rays. They are among the lowest radiation dose exams of any diagnostic radiologic procedure in the healing arts. Current practices deliver patient doses from a full-mouth series of intraoral films (usually 14–18 films) that are less than what a person receives in a month from natural environmental sources (commonly called background exposure). Doses from bitewing or panoramic films are even less. New technology is reducing the doses still further.

There is no limit on how many dental x rays you can have. The decision to have a dental x ray is based on the benefit of knowing whether or not there is a cavity, crack, or some other abnormality. So the decision to have them is based on what you and your dentist think.

I am looking for publications regarding dental radiation safety. Can you help?

In 2003 the National Council on Radiation Protection and Measurements published Report No. 145, Radiation Protection in Dentistry, which provides guidelines for radiation protection in dental practices. Generally, a state Department of Health (DOH) regulates the radiological practice portion in dentistry so you might check with your local state DOH. Its rules and regulations typically discuss training for individuals who operate x-ray equipment, equipment quality assurance, etc. Also, take a look at the websites shown below. The American Dental Association and American Dental Hygienists' Association sites provide information regarding continuing education, accreditation standards, and patient information related to dental radiography. You'll also be able to do a literature search on MEDLINE via the National Library of Medicine page.

• American Dental Association
• American Dental Hygienists' Association
• National Library of Medicine
• American Academy of Oral and Maxillofacial Radiology

A quick search on www.amazon.com resulted in several books, including Essentials of Dental Radiography for Dental Assistants and Hygienists (by Orlen Johnson), Radiation Protection in Dentistry: Recommended Safety Procedures for the Use of Dental X-Ray Equipment (unfortunately out of print), and Radiation Protection for Dental Radiography (by Cris Edwards, and also out of print).

What are the effective doses from various dental x-ray procedures? Can you compare them to some other radiation doses?

The table below compares effective doses from various dental x-ray procedures:

I recently was having a panoramic x ray when the machine got stuck on my shoulder about halfway through completing its arc. The dental hygienist released me in about 10–20 seconds. For the time between when the machine was stuck and when the dental hygienist released me, was I being exposed to radiation?

For a panoramic dental x ray, the beam is operating continuously as it makes the image. All panoramic x-ray units have a "deadman" switch or button that must be continually pressed by the operator to produce x rays. The production of x rays will stop immediately when the button is released, so x rays are produced until the hygienist releases the button. It is likely that the button was released immediately because it is also required that the hygienist constantly observes the operation of the unit so that he/she can stop the radiation if the unit fails to rotate properly or if the patient moves. Even if it took the hygienist a second or two to realize what occurred and release the button, the radiation dose would be insignificant.

What is the radiation dose difference between using standard film for a dental x ray and using digital radiography?

For intraoral radiographs (film packets placed inside the mouth) such as bitewings and periapicals, there are several types of film available at different speeds, meaning that they require different amounts of exposure to produce an image. This is a concept similar to photographic film speeds, with higher numbers requiring less light. A typical skin dose for Group D film (ultraspeed) is about 3.0 mGy, for Group E (Ektaspeed) about 1.5 mGy, and for Group F (Insight) about 1.1–1.2 mGy.

One digital-imaging manufacturer recommends setting the equipment at about 20 percent of D-speed film, or about 0.6 mGy. Another study found a 31–39 percent decrease compared with E-speed film for a different particular sensor. Some institutions have found that approximately a 50 percent decrease from F-speed film provides a good image.

One of the reasons that there is not much published on the specific amount of dose reduction is that most digital systems can use a fairly wide range of exposure times and then use software adjustments to provide a good image. It is possible that digital imaging may require as much exposure as film if the user does not consciously reset the x-ray machine to lower exposure or if the x-ray machine timer cannot accommodate the short exposure times (usually an old machine, not the current models).

With respect to digital panoramic radiographs, there appears to be no dose reduction compared with film-based panoramic images because there is already a large dose reduction as a result of use of intensifying screens in the panoramic cassettes.

I recently had some dental x rays and the operator forgot to place the lead apron on me. Is this a problem?

Use of the lead apron to protect the patient undergoing dental radiographic examination was recommended some 50 years ago, when equipment was crude. This was because x-ray beams were not restricted to the area of clinical interest, beams were not filtered, and x-ray film was slower, causing radiation exposures 10 to 100 times higher than received today. With the current technology reducing radiation exposure significantly and the beam limited only to the area of interest, there is little or no measurable difference in whole-body dose whether a lead apron is used or not. The lead apron is no longer regarded as essential, although some consider it a prudent practice, especially for pregnant and potentially pregnant females.

I had several dental x rays taken recently and am now having problems with my gums feeling hot and, in some areas, getting sores. Is it possible the dental x rays caused this?

The amount of radiation needed to cause biological effects is several hundred times higher than can be received during dental radiography. Because of the design of these x-ray machines, there is a limit to the amount of exposure possible during the procedure. Diagnostic dental radiation doses are very small and not known to cause biological effects of the type you describe or any other type.

Why do dental hygienists leave the room for each x ray?

It is general practice and, in many cases, a regulatory requirement for the dental technologists to leave the immediate area during the x-ray examination. Since the technologists are exposed repetitively to small amounts of radiation scattered from the large number of patients having dental x rays, it is considered good practice to reduce any risk they may have to an even smaller value.

Because of the location of a local dentist office, I used to live and work in a room next to the room containing the dental x-ray machine. Was I being exposed to radiation?

Exposure rates decrease rapidly with distance. Ordinary walls generally provide sufficient shielding for these machines. In fact, it has been considered "safe" for operators of these machines to be in the room as long as they were at least six feet from the x-ray tube. If you received any exposure, which is unlikely, it would be an insignificant amount.

Ask the Experts is posting information using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.