Dentistry: X-Ray Safety

At the American Dental Association convention in Dallas, there was disagreement over something that patients have long taken for granted: the safety of dental X rays. Although the A.D.A. has been encouraging the use of safer X-ray machines for years, many devices of antique design still adorn countless offices. Some have not even been equipped with an electronic timer, available since 1955, to go with the use of high-speed film and cut the exposure time to a fraction of a second. The vast majority still have, at their business end, a plastic cone three or four inches long. This makes aiming easier, but, unless specially insulated, it permits secondary radiation to scatter in all directions.

What the U.S. Public Health Service recommends, and the A.D.A. approves, is a machine that delivers an X-ray beam 2¾ in. in diameter. Extra-heavy aluminum filters weed out useless rays, and lead shielding keeps all radiation within bounds. The patient gets only a small fraction of the radiation that was sprayed out of pre-1958 machines.

Dr. Fred M. Medwedeff and Dr. William H. Knox of Nashville want even more safety than that. It is ridiculous, they say, to fire X rays at so big a circle when the target is a rectangle only 1 in. by 1½ in. To keep the X rays from fanning out, they must be “collimated”—made to follow parallel paths. In their machine, the Nashville dentists use a stainless-steel plate with a rectangular window to accomplish collimation; they also use much more shielding and a steel bracket to hold the film just where it ought to be, without subjecting the patient’s hand to radiation. The result, according to PHS tests, is a radiation dose delivered to the skin only one-half to one-fourth that from a recommended standard machine. Radiation to the cornea of the eye is reduced to one-eighteenth.

Some dentists dismiss such precautionary measures as too costly and unnecessary. But all radiation (except that used in medical treatment for specific diseases) is bad. The PHS urges that every patient’s body be protected with a lead apron, and it is backing several inventive dentists in their efforts to develop safer machines.