Relations between tooth positions and focal troughs of panoramic machines.

A comparison of the established focal troughs of three panoramic machines with positions of the teeth in the dental arches of 240 patients. The patients, divided into twelve cells, were selected on the basis of race, sex, age, number of teeth, and occlusion. Occlusal registrations were made in fast-set acrylic. Tooth centers were identified and, with the midline-incisal point as a reference point, various composite drawings of tooth positions of patients were made. The total composite of all teeth revealed the striking similarity of the arches. Superimposition on the focal troughs showed that the focal trough of the Panorex easily encompassed all tooth positions. The focal trough of the Orthopantomograph encompassed all tooth positions, although tooth centers lie on the edges of the trough. The focal trough of the GE-3000 with profile index 10 extended so far buccally that many teeth are positioned lingual to the trough. The focal trough of the GE-3000, when reduced uniformly to profile index 7.5, encompasses all tooth positions although some positions fall quite near the borders of the trough.