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Paralleling
Technique
Head Position
Head position for the paralleling technique is not critical,
since you will be aligning the PID with the ring. However,
since bitewing films are also taken on most patients, the
head should routinely be positioned as in the illustration
above (this is true when using bitewings with tabs). The
maxillary arch should be parallel to the floor, both side-toside and front-to-back. The head should always be
supported by the headrest.
correct
incorrect
In the paralleling technique, the film is positioned in the mouth
so that the long axis of the film and the long axis of the tooth
are parallel. We can not see the long axes of the teeth but, in
general, all the teeth incline toward the middle of the head.
Thus the film/instrument will almost always be tipped slightly
(up or down, depending on the arch). In the illustration above
right, the film is placed straight up and down and is not
parallel; the patient is unable to close completely on the
biteblock and the apices of the teeth would not appear on the
film.
Rinn XCP Paralleling Instruments
ANTERIOR
POSTERIOR
Anterior Periapical
Long axis of film (# 1 – adult; # 0 – small child) vertical. Colored
side against biteblock support; white side faces teeth/ring
(white-in-sight). Dot-end of film placed in slot of biteblock (dotin-the-slot).
dot
slot
dot
Posterior Periapical
Long axis of film (# 2 – adult, # 0 – small child) horizontal.
Colored side of film against biteblock support; white side
faces teeth/ring (white-in-sight). Dot-edge of film placed
in slot of biteblock (dot-in-the-slot).
dot
slot
dot
correct
incorrect
In general, the film should be positioned a reasonable distance
away from the teeth in order to allow the patient to close
reasonably comfortably and still maintain the parallel
relationship between teeth and film. The film will be closest to
the teeth in the mandibular molar region.
Ideally, we would like to have the long axis of the film parallel
with the long axis of the tooth. If the palate or floor of the mouth
is too shallow, the film usually cannot be positioned in this
manner. By tipping the film (see illustration above), we can
effectively position the film in the patient’s mouth. As long as the
film is not tipped more than 20 degrees from the line indicating
the long axis of the tooth, the image will be OK.
Make sure the patient is biting completely on the
biteblock as in the illustration above left. Sometimes the
patient will close their lips around the biteblock, looking
like they are biting down, but the biteblock is not in
contact with the teeth you are x-raying (illustration above
right). Make sure you can see the teeth in contact by
having the patient open their lips slightly.
The film above right shows the result of the patient not
biting on the biteblock. The apices are cut off.
Once the patient is biting on the biteblock, support the
bar with the fingers of one hand while sliding the ring
down with the other hand. The ring should be close to
the face. This will slightly reduce the amount of
exposure to the patient’s face.
Cotton rolls can be helpful in supporting the biteblock
in edentulous regions or where a tooth is tipped or
supraerupted. The cotton roll is placed against the
opposing arch, not between the biteblock and the teeth
being radiographed.
Maxillary Incisor
centered on contact between
central and lateral incisors
film placed far back in
patient’s mouth
Maxillary Canine
film centered on canine
film placed against the opposite
side of the arch, far away from
the canine
In the maxillary canine region especially, the film may tip to
one side or the other. A cotton roll is placed BETWEEN THE
BITEBLOCK AND THE MANDIBULAR TEETH (opposite arch) to
help keep the film aligned properly.
Maxillary Premolar
front edge of film anterior to
middle of canine; approximately
centered on 2nd premolar
film equidistant from lingual
surfaces of teeth (red arrows);
this opens contacts between
the teeth.
film in center of palate
Maxillary Molar
film centered on
second molar
film equidistant from lingual
surfaces of teeth (red arrows);
this opens contacts between
the teeth.
film in center of palate
top edge of PID above ring
Some patients, especially larger individuals, will have longer
than normal teeth. With the normal positioning of the film and
alignment of the beam, the apices of the teeth will be above
the edge of the film (not visible or “cut off”) as in the
illustration above left. To compensate for this, increase the
angle of the beam and raise the PID slightly (illustration
above right). You are purposely foreshortening the image.
If a patient has Tori (maxillary or mandibular):
palatal torus
Place film on the
opposite side of
palatal torus (away
from teeth being
radiographed); film
should not rest on
torus.
Place film between
torus and tongue,
making sure it
doesn’t rest on top
of torus.
mandibular torus
Mandibular Incisor
film centered on midline
film positioned away from
teeth, pushing tongue
back slightly
Mandibular Canine
film centered on canine
film positioned away from
teeth, pushing tongue
back slightly
Mandibular Premolar
front edge of film anterior to
middle of canine; approximately
centered on 2nd premolar
film equidistant from lingual
surface of teeth (red arrows);
film placed toward center of
mouth, displacing tongue
Mandibular Molar
centered on second molar
film equidistant from lingual surface
of teeth; in this case the film will
usually contact lingual of molars