A panoramic radiograph is a panoramic scanning dental X-ray of the upper and lower jaw. It shows a two-dimensional view of a half-circle from ear to ear. Panoramic radiography is a form of tomography; thus, images of multiple planes are taken to make up the composite panoramic image, where the maxilla and mandible are in the focal trough and the structures that are superficial and deep to the trough are blurred.
Normally, the person bites on a plastic spatula so that all the teeth, especially the crowns, can be viewed individually. The whole orthopantomogram process takes about one minute. The patient's actual radiation exposure time varies between 5.5 and 22 seconds for the machine’s excursion around the skull.
Other nonproprietary names for a panoramic radiograph are dental panoramic radiograph and pantomogram; trade names are Panorex and Orthopantomograph (genericized versions of the latter, such as orthopantomography or orthopantomogram, are best avoided in favor of the other nonproprietary names). Abbreviations include PAN, DPR, OPT, and OPG (the latter, based on genericizing a trade name, are often avoided in medical editing).
The collimation of the machine means that, while rotating, the X-rays project only a limited portion of the anatomy onto the film at any given instant but, as the rotation progresses around the skull, a composite picture of the maxillo-facial block is created. While the arm rotates, the film moves in a such way that the projected partial skull image (limited by the beam section) scrolls over it and exposes it entirely. Not all of the overlapping individual images projected on the film have the same magnification because the beam is divergent and the images have differing focus points. Also not all the element images move with the same velocity on the target film as some of them are more distant from and others closer to the instant rotation center. The velocity of the film is controlled in such fashion to fit exactly the velocity of projection of the anatomical elements of the dental arch side which is closest to the film. Therefore they are recorded sharply while the elements in different places are recorded blurred as they scroll at different velocity.
