Three-dimensional roentgenograms for improved oral diagnosis

Three-dimensional oral diagnosis Duane

J. Loetz,

roentgenograms

for

improved

D.D.S.

Fort Collins, Colo.

T

he primary difficulty in the use of three-dimensional roentgenolqgy -. has been the requirement of accurately positioning the film, the patient, and the roentgen tube. Previous three-dimensional viewers all required special skill on the part of the dentist and required a technique which was much too time-consuming to be practical in most dental offices. This article describes a method of using fixed lenses, a dental viewbox, and routine dental roentgenographic techniques that produces a three-dimensional effect. The dentist can use depth perception as an aid in interpreting roentgenograms when he is confronted with a difficult diagnostic problem. MAKING

THE

ROENTGENOGRAMS

In order to develop three-dimensional viewing, it is necessary to make two films of the same region, with a change in the position of the roentgen tube only (Fig. 1). The roentgenograms are positioned in the mouth with a mechanical holder, such as the Snap-A-Ray,* to insure that the location of the two films is as near to the same plane as possible. Three stereo pairs of films are exposed on each side in the posterior region: upper periapical, lower periapical, and bite-wing, in a routine full-mouth series of roentgenograms. A different procedure is required for the anterior teeth. Two films are made of the same region, each as near as possible to the same place, but with the tube head moved 3 to 4 inches in a horizontal plane (the central ray is directed at the center of the film in all instances). These two films are then used as a pair for stereo viewing. VIEWING

OF THE FILMS

The older three-dimensional techniques fixed the pictures to be viewed and the focal distance; the position of the lenses was adjusted for focusing purposes. The method described in this article fixes the focal distance and the position of the *Kinn

Corporation,

Chicago, Ill. 177

178

J. Pros. Dent. August, 1967

Loetr

Film position (example) for film no. 1 and (in Snap-A-Ray)

Fig. 1 A film holder is used to position x-ray films in the mouth. After one roentgenogram is made and removed, a second film is put in the same place, the x-ray tube is moved 4 inches before the second exposure is made.

lenses, and it allows the films to be moved freely on the viewbox until the images are superimposed and depth becomes apparent. If depth is not realized or if the image will not focus, the films are interchanged and will become clear. This phenomenon presents erroneous impressions of position because of accidental reversal of the films. CONSTRUCTING

THE VIEWER

Viewers for three dimensional-roentgenogram procedures are not commercially produced. However, the following directions are provided for the construction of a viewer. A rectangular magnifying glass, measuring about 1 by 2 inches with a focal length of about 8 inches, is used for the lens. It is not necessary to have high quality lenses since the amount of time spent with the viewer is short and infrequent. The

Volume Number

18 2

Three-dimensional

Perspective

(Cut

4 with

Original

roentgenograms

179

view

disc) lens

Lens

halves

in

use

Fig. 2 The design of the stereoptical

viewing device and its use.

lens is cut in half by means of a separating disc in order to form two square prismatic lenses. Rough edges are smoothed with stones normally used on porcelain restorations. The plastic mount is made from a sheet of Plexiglas.* Determination is made of the distance at which the surface of the viewbox is in clear focus through one prismatic lens. Then, the width of the lens plus 1 inch is added to indicate the total length of the sheet of plastic. The sheet of Plexiglas should be about 6 *Rohm

and

Haas,

Philadelphia,

Pa.

180

J. Pros. Dent. August, 1967

Loetz

Fig. 3 The stereoptical

viewer.

inches wide and from vs to ve inch thick. A second piece of plastic, about 4 inches by the focal length found above, is used for a leg. A line is drawn across the large sheet of Plexiglas at the focal length of the lens. The plastic is passed across the flame of a Bunsen burner, the heat being kept on the line on both sides until the material is soft enough to bend. The plastic is bent at a right angle and chilled in this position by cold water. Holes are cut in the top of the Plexiglas which are slightly smaller, but similar in shape to the lenses so that they can be mounted in line with the thickest part of the lens facing outward. Next, the part of the Plexiglas around the holes is heated (a pair of light gloves will prevent burning the hands), the lenses are forced into place, and the assembly is chilled in cold water. The center leg of the viewer can be made by cutting a piece of Plexiglas about 4 inches in length by the desired focal length and grinding it to an approximate fit with the bent piece. Then, the two pieces are attached with either a cement made for Plexiglas or with ordinary model airplane cement (Fig. 2). All of these materials are easily obtainable from hobby shops. If painting is desired, paints for plastics are also available. The finished stereoptical viewer is shown in Fig. 3. 1216 EMIOH FORT

COLLINS,

COLO.

80521