Reference Reading: Chapter 17; pp (up to step-by-step procedures)

Before the dental radiographer can competently perform the paralleling technique, he/she must have a thorough understanding of Terminology Principles Basic rules that govern this technique

Parallel: moving or lying in the same plane, always separated by the same distance and not intersecting

Intersecting: to cut across or through

Perpendicular: intersecting at, or forming a right angle

Right Angle: an angle of 90 degrees formed by 2 lines perpendicular to one another

Long Axis of the tooth: an imaginary line that divides the tooth longitudinally (from tip of crown to tip of root), into two equal halves

Central Ray: the center portion of the primary beam of radiation.

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The film is placed in the mouth PARALLEL to the long axis of the tooth being radiographed.

The central ray is directed perpendicular to both film and tooth

A beam alignment device must be used to hold the film parallel with the tooth. The patient cannot hold the film in this manner.

On maxillary arch, the film must be placed toward the middle of the oral cavity in order to achieve parallelism. This can result in increased image magnification.

To compensate for the image magnification, we use a long cone in the paralleling technique. Sometimes referred to as The Long Cone Technique

Using a long cone ensures that only the most parallel rays at the center of the x-ray beam will be directed at the tooth and film.

Film must be placed parallel to the tooth The central ray must be directed perpendicular to both film and tooth.

Film will be placed at mid-palate on the maxillary shots. (increased object-receptor distance) This increased DISTANCE between the film and the tooth can result in MAGNIFICATION.

To COMPENSATE for this magnification, we use a LONG CONE (16 inches). (increased target-receptor distance) This ensures that only the rays near the center of the x-ray beam form the image.