[Lead foil artifacts as a result of unintentional bending of dental X-ray films].

The lead foil of dental x-ray film packets may cause a number of artifacts; especially well known are the "tractor treads" and "herringbone patterns" following a backward filmpositioning in the patient's mouth. In the present paper a specific and seldomly occurring lead foil artifact is described which is caused by bending of the film packet. Four cases collected over a 5-year period are presented. Although different the four cases show a number of similarities. They appear as radiopaque areas covering the upper or lower halves of the films. Their borders show the characteristic "sandbar-pattern" previously described by the author. The explanation of their origin is that the patient has been occluding on a part of the film packet which has been bent to a nearly horizontal position. The x-rays directed against the edge of the lead foil will be absorbed causing irregular radiopaque areas on the film lined by "sandbar-pattern". When the film packet is bent, the lead foil will be stretched and drawn a little away from the edges of the films. Consequently the x-rays will be able to expose the edges of the films. Irregularities of the foil will give rise to concentric "bars". The lead foil is only of limited radiopacity, but due to the oblique direction of the x-rays through the foil the absorbing effect is intensified.