A method to maintain a constant magnification factor throughout the exposure of rotational panoramic radiographs.

The magnification factor can be held constant throughout the exposure of a panoramic radiograph by maintaining the physical centre of rotation equidistant from the central plane of the image layer. This may be accomplished with computer-controlled movement patterns while the effective centre of rotation follows a path selected to provide an optimal projection of the jaws. Theoretical considerations for creation of a constant magnification factor are presented and the practical implementation of the technique in a commercially available device (OrthOralix SD, Philips, Monza, Italy) is described. This technique minimizes distortion in panoramic radiographs and makes horizontal measurements possible in certain selected cases.