Paralleling Technique : Dental radiography for periapical X rays
Patient Preparation: Seat patient, adjust headrest, adjust chair height, place lead apron/thyroid collar, remove partial dentures.
Basic Principles of the Paralleling Technique
Ideally, the film is positioned parallel to the long axes of the teeth being radiographed. However, the film can be tipped as much as 20 degrees from parallel and the film will still be diagnostic. With this technique, the film is usually positioned at a distance from the teeth; this tends to decrease sharpness and increase magnification and blurring. Because of this, an extended target-film distance should be used. This can be accomplished using a longer PID and/or placing the x-ray tube on the opposite side of the tubehead from the PID.
Head Position for the Paralleling Technique
The patient can be upright or lying down; there is no special head position required. However, it is usually easier to have the head upright, with the arches parallel to the floor.
# 1 film: Used in the anterior region of the maxilla and mandible.
# 2 film: Used for all posterior films (May be used anteriorly, but is harder to position because of its increased width).
# 0 film: used anteriorly and posteriorly in children. If mouth is large enough, use the #1 or #2 as for adults.
Film holder: A film holding device (e.g., Rinn XCP) is usually used to position the film. This device has a bite-block for the film and a ring which helps to align the beam.
Place the film in the bite-block with the dot-side down (dot-in-the-slot).
The long axis of the film is vertical for anterior projections, horizontal for posterior projections.
Maintain an equal tooth-film distance along the entire length of the film.
The patient should gently close on the bite-block, making sure that the bite- block is in contact with the teeth being radiographed.
A cotton roll may be used for stability on the arch opposite the one being x-
rayed. A cotton roll may also be placed in an edentulous region in the same arch to fill in the space . A partial or complete denture may be used in the opposing arch.
Slide the ring down on the rod until it approximates the skin; support the rod with one hand while you do this.
Make sure head is supported by headrest before aligning PID with ring. Position the PID (cone) so that it is equidistant from the ring on the Rinn XCP instrument. The PID should be within 1/4″ of the ring.
Anterior-posterior film placement:
Maxilla: Film centered on the contact between the central and lateral incisors. Two films needed for the maxillary incisors (using # 1 size film).
Mandible: Film centered on the midline (Covers all four incisors).
Canine (both arches): Film centered on the canine.
Premolar (both arches): Anterior edge of film at least in the center of the canine. (Approximately centered on the second premolar).
Molar (both arches): Film centered on the second molar.
For people with long roots, increase vertical and raise or lower PID to center beam on film.
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