The Paralleling Technique- Part 1

Reference Reading: Chapter 17; pp. 156-158 (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

The Paralleling Technique

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

Terminology Intersecting: to cut across or through

Terminology Perpendicular: intersecting at, or forming a right angle

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

Terminology 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

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

Principles of the Paralleling Technique

OPEN TO PAGE 156 OF YOUR TEXTS

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

Incorrect Correct

Basic Principles The central ray is directed perpendicular to both film and tooth

Basic Principles A beam alignment

device must be used to hold the film parallel with the tooth.

The patient cannot hold the film in this manner.

Basic Principles-increased object-receptor distance 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.

Basic Principles- Increased target-receptor distance To compensate for the

image magnification, we use a “long cone” in the paralleling technique.

Sometimes referred to as “The Long Cone Technique”

Basic Principles 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.

Now…..to Review! 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.

REVIEW

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.

Review