1. Paralleling Technique
The following slides describe the
Paralleling Technique.
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2. Patient Preparation
Prior to starting to take films, the patient must
be positioned properly. Seat the patient and ask
them to remove their glasses and any removable
appliances. Adjust the headrest to support the
head while taking films. Raise or lower the chair
to a comfortable height for the operator. Place
the lead apron and thyroid collar on the patient.
You are now ready to begin taking films.
It is a good idea to inform the patient about the
number of films you will be taking so they know
what to expect.

3. In the paralleling technique, the film is placed in the
mouth so that the long axis of the film is parallel with
the long axis of the teeth being radiographed. A
paralleling instrument with an aiming ring is normally
used to orient the film, teeth and ring in a parallel
relationship. When the x-ray beam is aligned with the
ring, the x-ray beam will be perpendicular (right
angle) to the teeth and the film.
y
- ra
X
eam
b
Film/tooth/ring all parallel
X-ray beam perpendicular to tooth/film

4. Paralleling Technique (Advantages)
There are two techniques for taking periapical films, the
paralleling and the bisecting angle techniques. When
comparing the two techniques, the advantages of the
paralleling technique are:
1. Better dimensional accuracy: the paralleling
technique results in less distortion of the image of
the teeth. (The shape of the teeth and the
relationship of the teeth to surrounding structures
is more accurate).
2. When using the paralleling instrument with the
aiming ring, the alignment of the x-ray beam is
simplified.
(continued next slide)

5. Paralleling Technique (Advantages)
3. It is easier to standardize films. Because you are
using the positioning instrument, it is easier to
position the film in approximately the same
position at different appointments. This can be
helpful if you are trying to compare the
appearance of a periapical lesion from one visit
to the next.
4. Head position is not as critical. Because of the
paralleling instrument, with its aiming ring, it is
easy to properly align the x-ray beam no matter
how the head is positioned.

6. When the long axis of the film is parallel with the
long axis of the tooth, the image of the tooth on
the film looks the same as the tooth itself (no
distortion). The image will be slightly larger than
the actual tooth (magnification), but the shape is
the same.

7. Paralleling Technique (Disadvantages)
When comparing the paralleling and bisecting
angle techniques, the paralleling technique is:
1. Less comfortable. Because the film is
usually more upright when using the
paralleling technique, it impinges more on
the palate or floor of the mouth, thus making
it more uncomfortable.
2. More limited by the anatomy of the patient’s
mouth. A shallow palate or floor of the mouth
makes it harder to position the film using the
paralleling technique.

8. Paralleling Film Placement
As mentioned previously, the film is placed in the
mouth so that the long axis of the film is parallel with
the long axis of the teeth. Since all teeth are inclined
toward the middle of the head (not straight up and
down), the film will be slightly angled in the mouth
(see below left). If the film is maintained in an upright
position (below right), the patient will not be able to
close on the biteblock and the film will not be parallel.
correct
incorrect

9. Paralleling Film Placement
To facilitate film placement, the film may be tipped up
to 20 degrees beyond parallel.

10. Paralleling Film Placement
Because the palate and
floor of the mouth are
shallower as you approach
the lingual of the teeth, the
film often cannot be
positioned properly close to
the teeth.
As a result, the film must be
positioned away from the
teeth (farther back in the
mouth) to achieve parallelism.

11. Because the film is farther from the teeth, there will
be increased magnification (larger size) and
decreased sharpness (less detail). To compensate
for this, the target-film distance should be
increased (the target is where the x-rays are
produced).
size of image at 8” target-film distance
Target
16”
Target
8”
size of image at 16” target-film distance

12. The target-film distance is increased by using a longer
PID, using a machine with a recessed target (opposite
side of the tubehead from the PID) or a combination.
The medium PID with a recessed target is a good
compromise. The disadvantage to increasing the PID
length is that the exposure time must be increased. If
you change from an 8” target-film distance to a 16”
target-film distance (double the distance) the
exposure time will be four times as much (see Inverse
Square Law).
Long PID
Short PID
Recessed target
Medium PID
Recessed target

13. Paralleling Technique
Head Position
As mentioned previously, head position is not as
important when using the paralleling technique.
However, in general it is best to position the head
in an upright position so that the maxillary arch is
parallel to the floor.
Best
OK
OK

14. Paralleling Technique
Film Selection for Adults
The # 1 size film is used for anterior periapical films
using the paralleling technique. The long axis of the
film is vertical. For posterior films, # 2 size film is
used with the long axis horizontal.
#1
anterior
#2
posterior

15. Paralleling Technique
Film Selection for Children
For children with small mouths, the # 0 size film is
used for both anterior and posterior periapical
films. However, if the child’s mouth is large
enough to reasonably accommodate the larger
size films (# 1 anterior, # 2 posterior), and the child
is cooperative, they should be used.
#0
anterior
#0
posterior

16. Rinn Paralleling Instruments
The Rinn paralleling instruments are used at the Ohio
State University College of Dentistry. They are colorcoded, with yellow being the posterior instrument and
blue being the anterior instrument. The metal bar
connects to the side of the biteblock and the ring
slides on the bar.
POSTERIOR
ANTERIOR

17. The film is placed in the biteblock so that the all-white
side of the film packet faces the teeth and, by
extension, the ring. (The colored portion of the film is
against the back support of the biteblock). When you
look down through the ring, you should see the allwhite side of the film packet centered in the opening.
opposite
side
toward tube
front
back

18. Anterior Periapical
For the anterior periapical, the # 1 size film is placed
vertically in the biteblock. The film is rotated so the
identifying black dot is down; this end of the film goes into
the slot of the biteblock (dot-in-the-slot). Push the film
back against the biteblock support and slide it down into
the slot.
dot
F E Speed
1-Film
Kodak
INSIGHT
Dental Film
colored side of film
white side of film
slot
long axis vertical
white side facing teeth/ring

19. Posterior Periapical
For the posterior periapical, the # 2 size film is placed
horizontally in the biteblock. The film is rotated so the
identifying dot (faint embossed circle) is down; this side of
the film goes into the slot of the biteblock (dot-in-the-slot).
Push the film back against the biteblock support and slide
it down into the slot.
dot
OPPOSITE
SIDE
TOWARD TUBE
KODAK
INSIGHT
1- FILM F E
colored side of film
long axis horizontal
white side
of film
slot
white side facing teeth/ring

20. General Technique Guidelines
For all periapical films, the teeth being radiographed
must be in contact with the biteblock to avoid not having
the apices of the teeth on the film (see errors section of
slide show). Make sure patient doesn’t just close lips
tight around biteblock; have them part their lips so you
can confirm the contact.
correct
incorrect

21. General Technique Guidelines
As shown above, cotton rolls may be used in any area
of the mouth to help support the biteblock, especially
if an edentulous region or uneven teeth oppose the
teeth being radiographed. Using a cotton roll also
makes it more comfortable for the patient to bite in
some situations. The cotton roll should be placed
against the arch opposite the one being radiographed.

22. General Technique Guidelines
If a patient has a partial denture or a complete
denture in one of the arches, the appliance can
be used to help support the biteblock when the
patient closes. This is normally preferable to
using cotton rolls. Make sure that the denture is
only used in the arch opposite to the one being
radiographed. Partial dentures can not be left in
the arch being radiographed because the metal
framework will be superimposed over the images
of the teeth (see “Errors”).

23. General Technique Guidelines
After the patient is biting on the biteblock, and before
aligning the PID, the ring needs to be moved closer to
the patient’s face. While supporting the bar with the
fingers of one hand, slide the ring down close to the
face with the other hand.

24. General Technique Guidelines
Always make sure
the head is
supported by the
headrest before
aligning the PID
and exposing the
films.

25. General Technique Guidelines
The PID should be aligned with the ring so that the end
of the PID is equidistant from the ring and within ¼” of
the ring. The PID doesn’t have to touch the ring and the
placement doesn’t have to be perfect. Don’t spend
excessive time making adjustments when aligning the
PID. (Remember: the paralleling technique is not very
comfortable and the patient won’t appreciate any delays
in exposing the film).
PID
Correct
PID
PID
Incorrect
Incorrect
(not equidistant)
(not close enough)

26. Maxillary Central-lateral
The film is centered on the contact between the central and
lateral incisors. Make sure the mesial edge of the film
crosses the midline slightly (into the opposite central
incisor), to insure getting all of the central incisor crown on
the film. The film should be placed well back in the mouth,
away from the teeth, where the palatal vault is the highest.

27. Maxillary Central-lateral
This is a typical maxillary central-lateral periapical
film. Both the crowns and roots of the central and
lateral incisors (#’s 9 and 10 in this film) are
completely visible.

28. Maxillary Central-lateral
Although we routinely use the # 1
size film in the anterior region
because it is easier to place in
the mouth due to its narrower
width, it is also possible to use
the # 2 size film (for all anterior
projections). However, when the
# 2 size film is used for the
maxillary incisors, it is usually
centered on the midline, allowing
you to image all four incisors on
one film (the film at right is
slightly cropped, cutting off the
distal of the laterals).

29. Maxillary Canine
The film is centered on the canine. The film should
be placed well back in the mouth, away from the
teeth, where the palatal vault is the highest.

30. Maxillary Canine
Make sure the long axis of the film stays in line
with the long axis of the tooth when the patient
closes. If the film tips, place a cotton roll between
the biteblock and the mandibular teeth to keep
the film aligned with the canine.

31. Maxillary Canine
This is a typical maxillary canine
film (tooth # 11). Note the
overlap* (red arrow) between
canine and first premolar. This is
usually not avoidable in the
maxillary canine region using the
paralleling technique.
*overlap refers to the superimposition
of part of one tooth over a part of the
adjacent tooth. In this film, the mesial
of tooth # 12 is “overlapping” the
distal of # 11.

32. All Posterior Films
The film should be equidistant from the teeth in an
anterior-posterior direction (the distance from the
front edge of the film to the lingual surface of the
teeth should be the same as the distance from the
back edge of the film to the lingual surface of the
teeth, indicated by red arrows below). The film
should be positioned in this manner for both the
premolar and molar radiographs. This helps to avoid
overlap (see errors).
correct molar
premolar
incorrect
(results in overlap)

33. Maxillary Premolar
The film is positioned so that the anterior edge
is at least in the middle of the canine, or more
anterior if possible. The film is approximately
centered on the 2nd premolar. The top edge of
film is approximately in the center of the palate
(side-to-side).

34. Maxillary Premolar
The premolar film below shows the first and
second premolars and the first molar completely;
a portion of the second molar is also seen.

35. Maxillary Molar
The film is centered on the second molar. The top
edge of the film is in the center of the palate (sideto-side). The film should be centered on the second
molar even if the third molars are not present in
order to identify impactions, root tips or other
pathology that might be present in the third molar
region.

36. Maxillary Molar
The molar film below shows the first and second
molars and the third molar region (the third
molar has been extracted). The maxillary
tuberosity (red arrow) is easily identifiable.

37. Some patients may have a maxillary torus, which is a
bony growth in the center of the palate. If a palatal
torus is present, place the film so that the top edge is
on the opposite side of the torus (away from the teeth
being radiographed). The film should not rest on the
torus. (See diagram below).
palatal torus

38. 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 seen in the
film below. To compensate for this, increase the angle of the
beam and raise the PID slightly (illustration below right). You
are purposely foreshortening the image. You will not know
the teeth are longer from just looking at the patient, but if you
have taken previous films, or you get films from another
dentist, you can identify the need to alter your technique.
top edge of PID above ring

39. Mandibular Incisor
The film is centered on the contact between the central
incisors (midline). The film should be placed back in the
mouth, away from the teeth, as much as possible. The
bottom edge of the film is placed under the tongue and
as the film is uprighted into a parallel position, the
tongue is pushed back slightly.

40. For all mandibular
films, do not force
the film down into
the floor of the
mouth trying to get
the biteblock to
contact the occlusal
surface of the
mandibular teeth.
Position the film in a
parallel relationship
and let the patient
guide the film into
place as they close
their mouth. Have
the patient bite
slowly and gently.

41. Mandibular Incisor
The incisor film below shows all four mandibular
incisors. The distal aspects of the lateral incisors
are often cut off but you can see these areas on
the canine films. All four roots are clearly visible.

42. Mandibular Canine
The film is centered on the canine. The film should be
placed back in the mouth, away from the teeth, as much
as possible. The bottom edge of the film is placed under
the tongue and as the film is uprighted into a parallel
position, the tongue is pushed back slightly.

43. Mandibular Canine
This canine film shows the mandibular canine (#
22) and most of the lateral incisor and first
premolar.

44. Mandibular Premolar
The anterior edge of the film is positioned at least in the
middle of the canine, or more anterior if possible. The film
is approximately centered on the 2nd premolar. The film
should be placed more toward the middle of the mouth,
away from the teeth. This will be more comfortable for the
patient. However, this is usually the most uncomfortable
film taken on a patient using the paralleling technique.

45. Mandibular Premolar
This premolar film shows the mandibular first
and second premolars, the first molar and part of
the second molar.

46. Mandibular Molar
The film is centered on the 2nd molar. The film can be
placed closer to the teeth than in the premolar region.
This film is more comfortable than the premolar film
because the floor of the mouth is deeper in this region.

47. Mandibular Molar
This mandibular molar film shows the first and
second molars and the third molar region (the
third molar was extracted).

48. Some patients may have bilateral mandibular tori,
which are bony growths on the lingual of the mandible
in the premolar region. If tori are present, place the
film so that it is between the torus and the tongue.
Make sure the film doesn’t rest on top of the torus.
(See diagram below).
mandibular torus

49. Patients with longer teeth will also require an alteration in
technique in the mandibular arch. Increase the angle of the
beam (increase the negative vertical angulation, e.g., change
from - 20 degrees to - 35 degrees) and lower the PID slightly
(illustration below right). You are purposely foreshortening
the image.

50. Adult full-mouth series, Paralleling Technique
An adult full-mouth series of films consists of 15
periapical films; 7 anterior (from canine to canine,
4 maxillary and 3 mandibular) and 8 posterior
(premolar and molar films in each quadrant).
#2
R
#1
#2
L

51. Anterior First
When taking films on a patient, you should always
start with the anterior films. If you are doing a full
series, start with the maxillary canine film and
then finish all the anterior films, both maxillary
and mandibular. Then complete the posterior
films, starting with the premolar, then molar, in
each quadrant. When doing only a few films on a
patient, start with the most anterior film and work
your way back in the mouth. This sequence of
taking films allows the patient to get used to the
procedure with a minimum of discomfort and
helps to avoid stimulation of the gag reflex.

52. Paralleling Technique Errors
The following slides identify some of the most
common errors seen when using the paralleling
technique.

53. Film Placement
Poor film placement is the most common error seen
when using the paralleling technique. This usually
involves incorrect anterior-posterior positioning. The
premolar film is often not far enough forward and the
molar film is frequently not far enough back. The
premolar film below is placed properly. The molar film,
however, is too far forward, failing to image the third
molar region.
Premolar - OK
Molar - too anterior

54. Film Placement
In the anterior region, failure to properly center the film
is a common error. In the film below, the mesial of the
central incisor is not visible because the film was
positioned too far back. For the central-lateral film, the
film must cross the midline slightly in order to insure
that all of the central incisor will be seen.

55. Film Placement
If the patient is not completely closed and biting on the
biteblock (photo below), the top of the film will not be
positioned to show the ends of the roots (below right).
Usually the patient will tighten their lips around the
biteblock when this occurs; ask the patient to part
his/her lips so that you can make sure they are biting
properly.
roots cut off

56. Cone Cutting
Cone cutting occurs when part of the film is not covered
by the x-ray beam. It results in a white (clear) area on
the film because no silver halide crystals were exposed
and were not converted to black metallic silver during
processing. Using the paralleling instrument, it is very
easy to align the beam with the film. However, if the
instrument is not assembled properly (ring upside
down; see diagram below), cone-cutting will result.
correct
incorrect

57. Reversed Film
If the film is placed in the biteblock so that the colored
portion of the film packet faces the ring/teeth, the lead
foil in the packet will be between the teeth and the
film. The pattern imprinted on the lead foil will be
visible on the film (right side of film below) and the
film will be lighter because the lead keeps some of the
x-rays from reaching the film.

58. Double exposure
When taking films, you should always place each film in a
container or paper bag immediately after it is exposed.
Exposed films should never be placed in the same area
where unexposed films are located. If you inadvertently
pick up an exposed film and use it for another exposure,
the result is a double exposure. Two different areas of
the mouth are superimposed, making the images
worthless. This is the worst error because two films have
to be retaken.
The film at left shows
images of mandibular
incisors and mandibular
molars. The film was
vertical for the incisors and
horizontal for the molars.

59. Patient Movement
If the patient moves slightly during the exposure
of the radiograph, the image will be blurred as in
the film below. Always advise the patient to
remain still for the very short time it takes to
complete the exposure.

60. Overlap
As mentioned previously, the film must be kept
equidistant from the teeth when taking posterior
radiographs. If the film is not placed properly, as in the
diagram below left, overlapping will result due to the
improper horizontal angulation. Overlap is the
superimposition of part of one tooth with part of the
adjacent tooth (dotted circles below right). The red
arrow represents the direction of the x-ray beam.

61. Overlap
The radiograph below shows the overlap in the
region of the crowns of the teeth.

62. Incorrect Exposure Factors
The standard exposure settings on your x-ray machine
will be acceptable for the majority of your patients.
However, if you are taking radiographs on a child you
would need to decrease the settings. If your patient is
very large, you would need to increase the settings.
Underexposure results when the exposure factors are
set too low for the patient size. Overexposure results
when the exposure factors are set too high.
underexposure
correct exposure
overexposure

63. Glasses
It is recommended that glasses be removed before
taking radiographs, even if they are not expected to be
a problem (mandibular films or bitewing radiographs).
If the glasses are left on, they may be in the path of the
x-ray beam when taking maxillary films and produce
an image on the film (see below).
glasses

64. Failure to Remove Appliances
Removable partial dentures, as the name suggests,
should be removed prior to taking films. If the RPD is
left in place in the arch being radiographed, the image
of the RPD will obscure the necessary diagnostic
information. However, an RPD may be left in the mouth
in the arch opposite the one being radiographed in
order to support the biteblock. This is more effective
than using cotton rolls in the edentulous regions.

65. Film Bending
If you “soften” the film excessively by bending the
edges before placing the film in the biteblock, black
lines may be produced due to disruption of the
emulsion in the areas where the film was bent. These
black lines can also be caused by bending the film
when inserting it into the slot of the biteblock. If you
just push down on the film without pushing back on
the biteblock support, this bending may occur.

66. “Digit”al Image
Make sure the patient is biting firmly on the
biteblock before aligning the tubehead. Do not
allow the patient to hold the instrument in
position. If this happens, the patient’s finger may
appear on the film (red arrows on film below).

67. This concludes the section on Paralleling
Technique.
Additional self-study modules are available
at: http://dent.osu.edu/radiology/resources.htm
If you have any questions, you may e-mail
me at: jaynes.1@osu.edu
Robert M. Jaynes, DDS, MS
Director, Radiology Group
College of Dentistry
Ohio State University