Paralleling Radiographic Exposures:
The Preferred Method
XCP
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Key Terms to Know
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Parallel
Intersecting
Perpendicular
Right angle
Long axis of the tooth
Central ray
Basic Rules of ParallelingKnow
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Film placement
Film position
Vertical angulation
Horizontal angulation
Film exposure
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Principles of Paralleling Technique
A.
The film is placed in the mouth parallel to the long axis of the tooth
being radiographed
B. The central ray of the x-ray beam is directed perpendicular to the film
and long axis of the tooth
C.
Correct
A film holder must be used to keep the film parallel with the long axis
of the tooth
Incorrect
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Different Film Holding Devices
• Rinn XCP
Anterior
Posterior
• Stabe Bite-Block
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Parallel to the Long Axis of Tooth
Define long axis of tooth- *teeth to do not sit in the
mouth straight up & down
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Long Axis of Tooth
CORRECT
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Object and film/receptor are not parallel =
distortion
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Principles of Paralleling Technique
Remember:
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To achieve parallelism, the film must be placed away from the tooth and toward
the middle of the cavity
Object receptor (or film) distance must be increased to keep the film parallel to
the long axis of the tooth
Because of the distance from the film to the tooth, magnification and loss of
definition result. To compensate, the target receptor distance must be increased
(16 inch cone used-known as “long cone technique”). This results in less
magnification and increases definition.
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Object-Film-Distance v/s Target-FilmDistance
Compare/Contrast
object-receptor-distance & target-receptor-distance
(tooth to film)
(anode/focal spot to film)
*Both must be increased when using the
paralleling technique*
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REVIEW- Protection Measures
for the Patient
Source–film distance. The longer the source–film or receptor distance, the more parallel the
rays and the less tissue exposed. Note the beam size at the patient’s skin entrance is 2.75 in.
(7 cm) for both source–film distances; it is the exit beam size that increases to expose a larger
area when using the shorter source–film distance. Remember from safety module- 16”
cone preferred due to less divergence of x-ray beam as exits.
Challenges with Placement of Holder
 Conditions (i.e. crowding, mal-aligned teeth,
missing teeth, torus, size of mouth, vault of palate,
presence of unerupted 3rd molars, & variations in
occlusal relationship) affect ideal placement
 If the holder cannot be placed correctly- the beam
will not be aligned correctly = errors (distortion,
elongation, foreshortening, etc…)
 Patient conditions & cooperation do not always
match what textbook teaches! 
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Modifications of Placement
(see text)
 Shallow palate (p. 193- <than 20- degrees tilt acceptable; if
more -must modify)
 Maxillary/Mandibular tori (p. 207-209)
 Muscle attachments (p. 208-210)
 Missing teeth (use cotton rolls to stabilize)
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When holder tilted more than 20-degrees due to patient
conditions (and therefore NOT parallel to long axis) VERTICAL
ANGULATION needs to be INCREASED 5-15 degrees more
than indicated (therefore NOT lined up with circle of XCP)
**However, if angulation too excessive = incisal edges missing from image
& foreshortening
**If angulation inadequate (not enough) = apices missing & elongation
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Film Placement for each area
- *review handout & text
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ANTERIOR
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7-8
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9-10
2326
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Film Placement for Anterior
7 Size #1 films used for anteriors
Maxillary (4)
- canine (both sides)
- lateral/central incisors (both sides)
Mandibular (3)
- canine
- lateral/central incisors
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Film Placement for Posterior
8 (Size #2) films are taken in the posterior
Maxillary (4)
- premolar
- molar
Mandibular (4)
-premolar
-molar
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Need to see wisdom teeth
Center 2nd molar
Must see distal of canine on premolar PA
Center central/lateral contact
Center central incisors
Center canines
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Order for FMS
When using the paralleling technique, an exposure
sequence, or definite order for periapical film
placement and exposure, must be followed.
Keep track of exposures on tray cover!
This prevents
 Errors
 Loss of time
 Exposing the patient unnecessarily
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Order for FMS
I. Start with anterior exposure sequence (Size
#1 film used)
– Seven films are taken
– Begin with maxillary right canine-expose all
maxillary right
maxillary left
– Move to mandibular area-begin with mandibular
left canine and expose remaining films left to right
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Order for FMS Cont’d
2. Posterior exposure sequence (Size #2 film used)
-always expose the premolar first in all areas
-8 films are taken
-begin with maxillary right premolar then molar
-move to mandibular left –premolar then molar
(you do not have to reassemble XCP for this area)
-reassemble XCP and move to maxillary leftpremolar then molar
-finish with mandibular right area
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Order for FMS Cont’d
3. Lastly, take Bitewing radiographs (Size #2
film used)
- 4 radiographs are usually taken; horizontal BW
unless otherwise indicated
- BW part of FMS
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Advantages of Paralleling Technique
• Produces images with dimensional accuracy
• Is simple and easy to learn and use
• Is easy to standardize and can be accurately
repeated
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Disadvantages of Paralleling Technique
• Accurate film placement may be difficult at
times for the radiographer to achieve
• Film placement can sometimes be difficult for
the patient to tolerate (it hurts!)
• Not disposable- most holders have to be
sterilized
• Rings are a “guide” only- radiographer must
have skill to access accuracy
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Review helpful hints page 211!
Don’t forget to put the dot at the incisal edge now!
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