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X-Ray Safety For Children

How Much Exposure Is Too Much?

A Consultation with Dr. Johan Aps

Dear Doctor,
My dentist recently asked for permission to x-ray my child, saying it was necessary, but I'd like some more information. Are dental x-rays safe, and how often should children have them?

Cavity.

Dear Kim,
I can understand your concern; x-ray safety has been getting a lot of press coverage recently as the number of x-rays children are receiving for a variety of medical purposes increases. I'd like to emphasize one overriding point: The decision to use x-rays is always based on a risk-benefit analysis of the individual patient's unique set of circumstances.

What Are X-Rays?

X-rays are a form of invisible electromagnetic radiation (energy). One of their unique abilities is that they can penetrate human tissues. Depending on how dense the tissue is, more or less of the energy will be absorbed. This difference is what accounts for the images you can see on a radiograph (x-ray picture).

To create a radiograph that can help diagnose tooth decay, for example, a dentist will x-ray the tooth in question. On the opposite side of the tooth from the x-ray machine, the dentist will place a film or digital sensor in the mouth to record the image of any x-rays that reach it. Harder tissues such as teeth and bone will block most of the x-rays, leaving a white image. If tooth structure is lost because of decay (resulting in a cavity) the x-ray energy will pass through it, creating a darker image, which is captured on the film or sensor.

Healthcare professionals, who are trained to read radiographs, can interpret these pictures in detail, and detect changes that would never be obvious to the untrained eye. Radiographs are a vital part of diagnosis, allowing appropriate action and treatment. There's no question that this has been a tremendous boon to human health for more than 100 years.

Pros And Cons

There can be a downside to x-rays; they have the potential to cause biological effects within the tissues, especially rapidly growing tissues, which are more sensitive to radiation. This can increase the risk for changes in cells and very occasionally the potential for cancer. That's why, even at the very low doses used in dental diagnostics, x-rays are never to be used indiscriminately — especially with children.

X-tra Caution With Kids

According to the Food and Drug Administration, which regulates x-ray equipment, children's exposure to x-rays is of particular concern for three reasons:

  1. Younger patients are more radiosensitive than adults (i.e., the cancer risk per unit dose of x-radiation is higher for younger patients).
  2. Younger patients have a longer expected lifetime for the effects of radiation exposure to manifest as cancer.
  3. Use of equipment and exposure settings designed for adult use can result in excessive radiation exposure for the smaller patient. All modern x-ray units have settings for children to allow the correct x-ray dosage.

ALARA

Once the decision to x-ray a patient is made, all health professionals are advised to follow the ALARA principal for radiation dosage, which is an acronym for “as low as reasonably achievable.” Fortunately, with today's high-speed film and digital x-ray equipment, which is becoming standard in dental offices across the country, extremely low-dose x-rays are possible.

No professional dental organization advocates making x-ray use routine. The American Dental Association and the American Academy of Pediatric Dentistry both recommend that x-rays be used only after a clinical examination of the patient, and a review of his or her medical history and any prior use and frequency of radiographs.

A good example of very safe use of x-rays in children is a set of two or four bitewing radiographs, depending on the number of teeth in the child's mouth. Bitewings are so-called for the little tabs or wings attached to the films or sensors upon which one bites. They are indispensable for detecting decay between the back teeth where cavities can hide. They are very safe, exposing a child to less radiation than he or she would receive normally each day from natural background sources in the environment: Normal background radiation on average is 3600 microsieverts per year, which equals about 10 microsieverts per day. Two bitewing x-rays will expose a child to a dose of just 2 microsieverts of radiation. The number of bitewing sets that are necessary per year depends on your child's risk of tooth decay, but they should be spaced at least 6 months apart.

So How Do You Decide?

Nearly every diagnostic testing procedure carries some risk, so it's always important for you and your healthcare provider to do a risk-benefit analysis. More often than not, the information yielded is necessary for your long-term health and certainly outweighs the risk of the testing.

The best thing you can do at this point is to ask your dentist why he or she is suggesting x-ray use, how the information it yields will affect your child's healthcare, and why that information can't be obtained any other way.

Your question tells me that you need more information about the risks, benefits and alternatives to x-rays in your own child's case to make an informed decision. Your dentist should be happy to fill in the blanks.

Precautions Taken To Ensure X-Ray Safety

  • Modern x-ray machines are designed to avoid scattered radiation, ensuring x-rays are only emitted in a single beam.
  • For radiographs inside the mouth, the x-ray beam should be collimated (restricted) to the size and shape of the film or digital sensor that is being used.
  • In addition, all structures not being x-rayed are shielded; lead aprons and neck shields should be placed to protect other areas.
  • Modern high-speed films and digital sensors enable x-ray images to be generated at short exposure times, which limits the patient's dose.


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