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Welcome. In navigating through the slides, you
should click on the left mouse button when (1), you
see the mouse holding an x-ray tubehead (seebelow), (2) you are directed to click for the next
action and (3) you are done reading a slide. Hitting
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to the previous slide, hit backspace or page up.If you right click anywhere on the screen and select
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The following slides describe
Object Localization, including the
Right Angle Technique and the
Tube Shift Technique.
Object Localization
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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 twoprimary 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, Clarks rule)
Utilizes two films with different horizontal or vertical
angulations
Object Localization
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Right Angle (Occlusal) technique
Right Angle Technique
Once you have identified an object on the periapicalfilm, 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 linguallypositioned.
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Tube-Shift Localization (Clark)
SLOB RuleSame Lingual Opposite Buccal
The SLOB rule is used to identify the buccal orlingual 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.
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For the SLOB rule to work, there must be a
change in the horizontal or vertical
angulation of the x-ray beam as the tubeheadis 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 linguallocation.
The closer the object to be localized is to thereference object, the less the amount of
movement of the image of the object in
relation to the reference object.
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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).
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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, thedirection 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.
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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 tubeheadis 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).
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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 directedmore 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.
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In the diagram at left, the
buccal (yellow) and lingual
(red) objects of interest are
superimposed on each other
because the beam is directedperpendicular to both of them
and they are in the same
relative position mesiodistally
and vertically. Both images arelocated above the second
molar.
mesial
distal
mesialdistal
Horizontal movement
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In the diagram at left, the
tubehead is moved distallyand 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 astubehead) in relation to the
second molar.
mesialdistal
mesial
distal
Horizontal movement
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In the diagram at right, thetubehead 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) movesmesially (same direction as
tubehead) in relation to the
second molar.
mesial
distal
mesialdistal
Horizontal movement
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In the diagram at left, the
buccal (yellow) and lingual
(red) objects of interest are
superimposed on each other
because the beam is directedperpendicular 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
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In the diagram at left, thetubehead 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
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In the diagram at left, thetubehead 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) movesdown (same direction as
tubehead) in relation to the
second premolar.
Vertical movement
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Usually when using the tube-shift method of
localization, two films are taken of the same areausing 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 determiningwhich 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).
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For the films above, we know that the tubehead was moveddistally 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
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Richards Method of Object Localization
This method of determining the buccolinguallocation of objects was first suggested by
Richards. It utilizes similar ideas to Clarks
method, but it emphasizes beam direction instead
of tubehead movement. If the beam is directeddistally, 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 iseasier to use tubehead movement (SLOB) for
object localization.
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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.
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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.
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canine filmpremolar 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).
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PID
lingual
buccal
When the tubehead is moved mesially, with the beamdirected 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.
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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 filmand 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 thepost located?
The post is located in the lingual canal. As the
tubehead moves distally from the canine film tothe premolar film, the post also moves distally
to cover the canal that has all gutta percha.
3
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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 movingfrom the premolar periapical to the
bitewing, the tubehead moves
down and the premolar also moves
down. The displacement is to the
lingual.
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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.
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film placement for canine filmfilm placement for premolar film
root tip
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7
The maxillary right lateral incisor is tilted out of position.
In which direction (buccal or lingual) is it tipped?
premolar film incisor film
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incisor film canine film8
The maxillary left canine is impacted. Is it located more
to the buccal or the lingual?
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premolar periapical film
premolar bitewing film
10
The mandibular second
premolar is tilted out of
position. In whichdirection (buccal or
lingual) is it tipped?
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premolar film molar film
12
Does the arrow point to the mesiobuccal or mesiolingual
canal?
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molar bitewing film
molar periapical film
13
The amalgam particle
indicated by the arrows
is located bucally or
lingually?
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Is the restoration
indicated by the red
arrows located on thebuccal or lingual of the
first premolar?
canine periapical film
premolar periapical film
premolar bitewing film14
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15
incisor film canine film
premolar film
The gutta percha root canal filling identified by the red
arrows is located in which canal?