Positioning errors account for the majority of problems associated with obtaining a readable panoramic image. A panoramic X-ray unit rotates in a path about a vertical axis and creates a vertically oriented three dimensional zone of focus, or focal trough. The panoramic X-ray machine’s primary function is to create this focal trough of the dental arch. The focal trough is located where the patient places their chin on the chinrest. The objective of the operator is to position the patient’s Frankfort Plane horizontally, center their midline and locate the patient front-to-back within this focal trough.

FRANKFORT PLANE

The Frankfort Plane should be aligned horizontally to position the upper dental arch over the lower dental arch in one vertical plane. When correctly positioned, the upper and lower dental arch will fit vertically within the focal trough. If the Frankfort plane is over-rotated or under-rotated, the upper and lower dental arch will be passing through the focal trough at an angle in the anterior region. The resulting image will have distortion in the anterior portion of the film through the maxillary and mandibular regions such as foreshortening of the root tips, superimposition of the hard palate across the maxillary root tips, as well as blurriness to the dentition that extends beyond the edges of the focal trough.

MIDSAGITTAL PLANE OR PATIENT MIDLINE

The patient’s midline is centered to ensure that the dental arch is positioned laterally within the focal trough. If the patient is not centered within the focal trough, the dental arch will be positioned such that one side of the arch is closer and the other is farther from the film. This results in an increase in magnification on one side of the image and a decrease in magnification on the other. Another negative result is an increase in the amount of inherent overlapping of the teeth because the X-ray beam is not passing perpendicularly through the dental arch.

CENTERING FRONT-TO-BACK OR CUSPID POINTER ALIGNMENT
Centering the patient front-to-back within the focal trough is needed to ensure proper magnification throughout the anterior portion of the film as well as keep inherent overlapping to a minimum. In order to center the patient front-to-back within the focal trough, three methods have been used in the production of Panoramic’s PC-1000 models. In models with a serial number of 1,000 and greater, an adjustable chinrest was incorporated with a metal pointer; the chinrest would be adjusted until the pointer was aligned to the lower cuspid of the patient. In models with a serial number of 2,000 and greater, the same adjustable chinrest was used in conjunction with a plastic pointer; the chinrest was adjusted until the lower cuspid was aligned with the red line on the plastic pointer. In models 6,000 through current production, the adjustable chinrest was eliminated due to engineering changes that increased the focal trough significantly. This increase in focal trough size allowed the adjustable chinrest to be eliminated, making the PC-1000 one of the simplest machines to get consistent quality films.

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