Excessive dental X-rays can expose both children and adults to unnecessary radiation and expense. (Kids Smile Inc./Kids Smile Inc.)

Many years ago, Jay W. Friedman, a Los Angeles dentist, referred a woman to a renowned periodontist. A few years later, she told Friedman that the periodontist exposed her every year to a full-mouth periapical X-ray that showed her teeth from root to crown. Friedman told her that gum disease progresses very slowly and that she didn’t need those yearly X-rays, which require more than a dozen exposures. She told the periodontist, and he told her to find another one — which was really good advice.

Used appropriately, radiography is a valuable tool that enables dentists to diagnose dental caries (cavities) that attack teeth, gum disease that destroys the bone around teeth, the position of unerupted wisdom teeth, the type and degree of orthodontic malocclusion, and many other conditions. But when overused, X-rays can expose patients to unnecessary radiation and expense in exchange for little or no benefit.

Economics also factor into overuse: Dental X-rays are a large source of income for many practitioners. And some dentists think X-rays are necessary to protect them from malpractice suits, when in truth the best protection is proper dental practice.

X-rays you don’t need

There are few evidence-based studies about the appropriate use of dental X-rays, but there is broad agreement that they shouldn’t be overused because of the cumulative radiation risk, especially for children. One study, “Dental X-Rays and Risk of Meningioma,” published online in the April 2012 issue of the journal Cancer, found an association between higher exposure to dental X-rays, especially during childhood, and the development of meningioma, the most common type of brain tumor. (Fortunately, the tumor is usually benign.) No responsible dentist today would recommend annual full-mouth periapical X-rays like the ones that Friedman’s patient had. But other types of X-rays are also used inappropriately. They include:

●Routine bitewings — images that show the crowns of upper and lower teeth — during annual checkups.

●Full-head and jaw X-rays (cephalographs) before starting routine orthodontic treatment.

●Panographs — panoramic images of the teeth and entire jaw — to evaluate temporomandibular joint (TMJ) pain.

●3-D cone-beam computed tomography (the latest fad) — similar to a CT scan but with far more radiation exposure — for orthodontics or routine wisdom-tooth extractions.

Dentists are not infallible. It’s easy for them to overlook a cavity, an abscess or even a large cyst, all of which often take years to develop. That’s why at each examination your dentist should look at previous X-rays as if they were brand-new to make sure nothing was missed before deciding on whether additional ones are needed.

X-rays you do need

Here is Friedman’s guide to the appropriate use of dental X-rays, which is consistent with the American Dental Association’s guidelines. Bear in mind that there are always exceptions to guidelines, but they should be based on symptoms that lead your dentist to suspect something is wrong.

Children. If there are no spaces between the teeth, bitewing X-rays of the rear teeth should be taken at the initial examination. Bitewings should be repeated in 18 to 24 months for children at low risk with few or no cavities, and in 12 to 18 months for children with many cavities.

Adults. Full-mouth X-rays (periapicals or a panograph) and bilateral bitewing X-rays should be taken at the initial examination. Copies of X-rays taken by a previous practitioner within the past few years can be used if the patient has no new symptoms. For adults with few or no cavities, repeat bitewings in two to three years. For cavity-prone adults, bitewings should be repeated in 18 months, which is about how long it takes for a new cavity to become visible on an X-ray. In the absence of reasons to expect some new dental disorder, it’s not necessary to repeat full-mouth X-rays in less than 10 years, if at all.

For routine orthodontic treatment, wisdom-tooth extractions and temporomandibular joint disorders, avoid full-head films, 3-D cone-beam computed tomography scans and special TMJ X-rays.

Today’s dentists are more open to consumer concerns but may still be resistant to change. You may have to be persistent in rejecting unnecessary X-rays.

Copyright 2012. Consumers Union of United States Inc.