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The Paralleling Technique- Part 1
Reference Reading: Chapter 17; pp. 156-158 (up to “step-by-step
procedures”)
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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
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Terminology Parallel: moving or lying in the same plane, always separated by the same distance and not intersecting
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Terminology Intersecting: to cut across or through
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Terminology Perpendicular: intersecting at, or forming a right angle
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Terminology Right Angle: an angle of 90 degrees formed by 2 lines perpendicular to one another
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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
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Terminology Central Ray: the center portion of the primary beam of radiation.
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Principles of the Paralleling Technique
OPEN TO PAGE 156 OF YOUR TEXTS
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Basic Principles The film is placed in the mouth PARALLEL to the long axis of the tooth being radiographed.
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Incorrect Correct
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Basic Principles The central ray is directed perpendicular to both film and tooth
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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.
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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.
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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”
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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.
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Now…..to Review! Film must be placed
parallel to the tooth
The central ray must be directed perpendicular to both film and tooth.
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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
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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