Here are the answers to slides 7 through 15: 7. Lingual 8. Lingual 9. Buccal 10. Lingual 11. Lingual 12. Mesiolingual 13. Lingual 14. Lingual 15. Mesiobuccal

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2. The following slides describe
Object Localization, including the
Right Angle Technique and the
Tube Shift Technique.
Object Localization

3. A periapical film will identify the location of an object
vertically and in a horizontal (mesiodistal) direction.
However, we cannot tell where the object is located
buccolingually, since the periapical film is two-
dimensional. Therefore we need another method for
locating objects in a buccolingual direction. The two
primary methods of determining the buccolingual
location of objects are:
Right-Angle Technique (Occlusal projection)
Primarily identifies buccolingual location, but may
also confirm mesiodistal location seen on periapical
Tube-shift Technique (SLOB rule, Clark’s rule)
Utilizes two films with different horizontal or vertical
angulations
Object Localization

4. Right Angle (Occlusal) technique
Right Angle Technique
Once you have identified an object on the periapical
film, you can take an occlusal film with the beam at a
right angle (perpendicular) to the direction of the beam
for the periapical. The beam may also be perpendicular
to the film, especially in the mandible. The occlusal film
below shows that the impacted canine is lingually
positioned.

5. Tube-Shift Localization (Clark)
SLOB Rule
Same Lingual Opposite Buccal
The SLOB rule is used to identify the buccal or
lingual location of objects (impacted teeth, root
canals, etc.) in relation to a reference object
(usually a tooth). If the image of an object moves
mesially when the tubehead is moved mesially
(same direction), the object is located on the
lingual. If the image of the object moves distally
when the tubehead moves mesially (opposite
direction), the object is located on the buccal.

6. For the SLOB rule to work, there must be a
change in the horizontal or vertical
angulation of the x-ray beam as the tubehead
is moved. This change in angulation will alter
the relationship between the object of
interest and the reference object, allowing
you to determine the buccal or lingual
location.
The closer the object to be localized is to the
reference object, the less the amount of
movement of the image of the object in
relation to the reference object.

7. In the diagram at right, the
tubehead is moved, but there is no
change in direction of the x-ray
beam, which results in no change
in location of the object of interest
in relation to reference object (see
below). Moving the tubehead
without changing the beam
direction would often result in a
cone cut , depending on how far
the tubehead is moved (see below
right).

8. When using the SLOB rule, the direction of the beam
must be opposite to the way the tubehead is moved.
Horizontal Tube Shift: When the tubehead is moved
mesially, the beam must be directed more distally
(from the mesial). If the tubehead is moved distally, the
direction of the beam must be more towards the mesial
(from the distal).
Vertical Tube Shift: The SLOB rule also works for
movement of the tubehead in a vertical direction.
Downward movement of the tubehead requires that the
beam be directed upward and when the tubehead is
moved upward, the beam must be directed downward.

9. Moving the tubehead mesially or distally and changing the
direction of the x-ray beam (as described in the previous slide) will
result in the movement of the object of interest on the film in
relation to the reference object. In the diagram below, the tubehead
is moved distally with the x-ray beam directed more mesially (from
the distal). The object of interest, located lingual to the first molar,
moves distally, in the same direction as the tubehead movement.
(Objects closer to the film move less distance than objects farther
from the film; in the example shown below, both the tooth and
object move forward on the film, but the lingual object , being
closer to the film, moves less and “appears” to move distally in
relation to the tooth).

10. incisors
canine
premolar
molar
Horizontal movement of the tubehead and x-ray beam
In moving from the incisor film to the canine film, the
canine film to the premolar film and the premolar film to the
molar film, the tubehead moves distally and the beam is
directed more mesially. There is not much change in
angulation from the premolar to the molar film; the normal
situation would be that the beam is directed slightly more
from the distal (or to the mesial) as the tubehead is moved
distally for the molar projection.

11. In the diagram at left, the
buccal (yellow) and lingual
(red) objects of interest are
superimposed on each other
because the beam is directed
perpendicular to both of them
and they are in the same
relative position mesiodistally
and vertically. Both images are
located above the second
molar.
mesial
distal
mesialdistal
Horizontal movement

12. In the diagram at left, the
tubehead is moved distally
and the beam is directed
mesially. On the radiograph,
the buccal object of interest
(yellow) moves mesially
(opposite to tubehead
movement) in relation to the
second molar and the lingual
object of interest (red) moves
distally (same direction as
tubehead) in relation to the
second molar.
mesialdistal
mesial
distal
Horizontal movement

13. In the diagram at right, the
tubehead is moved mesially
and the beam is directed
distally. On the radiograph,
the buccal object of interest
(yellow) moves distally
(opposite to tubehead
movement) in relation to the
second molar and the lingual
object of interest (red) moves
mesially (same direction as
tubehead) in relation to the
second molar.
mesial
distal
mesialdistal
Horizontal movement

14. Maxillary PA
BW
Mandibular PA
Vertical movement of the tubehead and x-ray beam
In moving from the maxillary periapical to the bitewing
and from the bitewing to the mandibular periapical, the
tubehead moves down and the beam is redirected
upward (opposite direction; decreased vertical
angulation).

15. In the diagram at left, the
buccal (yellow) and lingual
(red) objects of interest are
superimposed on each other
because the beam is directed
perpendicular to both of them
and they are in the same
relative position mesiodistally
and vertically. Both images are
superimposed over the
mandibular second premolar.
Vertical movement

16. In the diagram at left, the
tubehead is moved upward
and the beam is directed
downward. On the radiograph,
the buccal object of interest
(yellow) moves down
(opposite to tubehead
movement) in relation to the
second premolar and the
lingual object of interest (red)
moves up (same direction as
tubehead) in relation to the
second premolar.
Vertical movement

17. In the diagram at left, the
tubehead is moved downward
and the beam is directed
upward. On the radiograph,
the buccal object of interest
(yellow) moves up (opposite
to tubehead movement) in
relation to the second
premolar and the lingual
object of interest (red) moves
down (same direction as
tubehead) in relation to the
second premolar.
Vertical movement

18. Usually when using the tube-shift method of
localization, two films are taken of the same area
using different beam angulations. However, this
localization technique will also work when
comparing films taken as part of a complete series
of radiographs. The only difficulty is determining
which way the beam was directed when
comparing the molar and premolar films. Usually
this can be done by comparing the relative
positions of anatomical structures (e.g., zygomatic
process in maxilla or mental foramen in mandible)
or the angulation of the roots of the teeth.
(See following two slides).

19. For the films above, we know that the tubehead was moved
distally from the premolar to the molar film. The zygomatic
process (red arrows) is located at the distal aspect of the
2nd
molar on the premolar film and it is located over the
distal aspect of the 1st
molar on the molar film. This
indicates that it moved mesially as the tubehead moved
distally. We know that the zygomatic process is buccal to
the teeth and, using the SLOB rule, it follows that the x-ray
beam was directed more mesially on the molar film (Buccal
object moved opposite to tubehead movement).
premolar molar

20. premolar molar
Another way of determining the change in the direction of
the beam is to look at the angulation of the teeth. In the
premolar film, the roots of the teeth are angled distally,
indicating that the beam was directed distally (from the
mesial). In the molar film, the roots are more upright or
angled slightly mesially, indicating the beam was directed
more mesially (from the distal). Therefore, the tubehead
shifted distally and the beam was angled in the opposite
direction, allowing the use of the SLOB rule (These films
were taken from Slide 3 in the review films to follow).

21. Richard’s Method of Object Localization
This method of determining the buccolingual
location of objects was first suggested by
Richards. It utilizes similar ideas to Clark’s
method, but it emphasizes beam direction instead
of tubehead movement. If the beam is directed
distally, buccal objects will move distally in
relation to the reference object; lingual objects
move mesially, or opposite to beam direction.
Although this method certainly works, I feel it is
easier to use tubehead movement (SLOB) for
object localization.

22. On the following six pre-test slides, identify the
buccal or lingual location of the selected objects.
Each slide will be followed with a slide indicating
the correct response and a brief explanation.

23. Is the composite restoration on tooth # 8 (arrows)
located on the buccal or lingual?
canine film incisor film1
The restoration is located on the buccal. The tubehead
moves mesially from the canine film to the incisor film
(x-ray beam projected more distally) and the composite
moves distally, which is the opposite direction.

24. canine film
premolar film
The arrow in the canine film is pointing to the gutta
percha in which canal of the maxillary first premolar?
2
The arrow identifies the lingual canal. The tubehead moves
mesially from the premolar film to the canine film (beam
directed more distally) and the gutta percha indicated by
the arrow also moves mesially. (See following slide).

25. PID
PID
lingual
buccal
When the tubehead is moved mesially, with the beam
directed distally, the two canals, which are initially
superimposed (premolar periapical above) will separate. The
lingual canal (red arrow) will follow the tubehead movement
and the buccal canal (blue arrow) will move in the opposite
direction, as seen on the canine film.

26. The red arrow is pointing to the gutta percha in
which canal of this maxillary left first premolar?
This is the buccal canal. The tubehead goes
distally from the canine film to the premolar film
and the gutta percha moves mesially to be
positioned over the lingual canal which has the
threaded post.
The pink arrow points to a threaded post. In
which canal of this maxillary left second premolar
is the post located?
The post is located in the lingual canal. As the
tubehead moves distally from the canine film to
the premolar film, the post also moves distally
to cover the canal that has all gutta percha.
3

27. Is the maxillary second
premolar (arrows)
displaced to the buccal
or the lingual?
premolar film molar film
premolar bitewing
4
The tubehead moves distally from
the premolar film to the molar film.
The second premolar also moves
distally, overlapping the first molar
more in the molar film. In moving
from the premolar periapical to the
bitewing, the tubehead moves
down and the premolar also moves
down. The displacement is to the
lingual.

28. incisor film canine film
Is the displaced incisor (arrows) located on the buccal
or the lingual?
5
The lateral incisor is displaced to the lingual. The
tubehead moves distally from the incisor film to the
canine film. The lateral incisor also moves distally,
covering half the canine on the canine film.

29. canine film
premolar film
Is the radiopaque object identified by the arrows located
on the buccal or the lingual?
6
Lingual. The tubehead moves mesially from the premolar
film to the canine film. The object also moves mesially,
starting out distal to the first molar on the premolar film and
ending up mesial to the first molar on the canine film. This
object represents the tip of the palatal root of the second
molar and is located distal to the first molar and in a lingual
relationship (See following slide).

30. film placement for canine film
film placement for premolar film
PID placement forpremolar film
PID placement for canine film
root tip

31. For slides 7 through 15, identify
the buccal or lingual location of
the structures indicated. Enter
answers on the answer sheet
provided.

32. 7
The maxillary right lateral incisor is tilted out of position.
In which direction (buccal or lingual) is it tipped?
premolar film incisor film

33. incisor film canine film8
The maxillary left canine is impacted. Is it located more to
the buccal or the lingual?

34. premolar bitewing film
9
The amalgam restoration
indicated by the arrow is
located on the buccal or
the lingual?
premolar periapical film

35. premolar periapical film
premolar bitewing film
10
The mandibular second
premolar is tilted out of
position. In which
direction (buccal or
lingual) is it tipped?

36. molar bitewing film
molar periapical film
11
The arrow points to a
retention pin. Is the
pin located in the
buccal or lingual
portion of the tooth?

37. premolar film molar film
12
Does the arrow point to the mesiobuccal or mesiolingual
canal?

38. molar bitewing film
molar periapical film
13
The amalgam particle
indicated by the arrows
is located bucally or
lingually?

39. Is the restoration
indicated by the red
arrows located on the
buccal or lingual of the
first premolar?
canine periapical film
premolar periapical film
premolar bitewing film14

40. 15
incisor film canine film
premolar film
The gutta percha root canal filling identified by the red
arrows is located in which canal?