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 (see below), (2) you are directed to

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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 (see
below), (2) you are directed to click for the
next action and (3) you are done reading a slide.
Hitting Enter or Page Down will also work. To
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Object Localization
The following slides describe Object
Localization, including the Right Angle Technique
and the Tube Shift Technique.
3
Object Localization
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, Clarks rule)
Utilizes two films with different horizontal or
vertical angulations
4
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.
Right Angle (Occlusal) technique
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
Horizontal movement of the tubehead and x-ray beam
incisors
canine
premolar
molar
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.
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mesial
Horizontal movement
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.
distal
mesial
distal
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Horizontal movement
mesial
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.
distal
mesial
distal
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mesial
Horizontal movement
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.
distal
mesial
distal
14
Vertical movement of the tubehead and x-ray beam
Maxillary PA
BW
Mandibular PA
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
Vertical movement
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.
16
Vertical movement
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.
17
Vertical movement
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.
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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).
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premolar
molar
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).
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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).
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Richards Method of Object Localization
This method of determining the buccolingual
location 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 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.
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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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1
canine film
incisor film
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Is the composite restoration on tooth 8
(arrows) located on the buccal or lingual?
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 film
premolar film
The arrow in the canine film is pointing to the
gutta percha in which canal of the maxillary
first premolar?
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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lingual
PID
buccal
PID
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.
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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 red arrow is pointing to the gutta percha in
which canal of this maxillary left first premolar?
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.
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4
premolar film
molar film
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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.
Is the maxillary second premolar (arrows)
displaced to the buccal or the lingual?
premolar bitewing
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5
incisor film
canine film
0
Is the displaced incisor (arrows) located on the
buccal or the lingual?
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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6
canine film
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premolar film
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).
Is the radiopaque object identified by the arrows
located on the buccal or the lingual?
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PID placement for canine film
PID placement for premolar film
root tip
film placement for canine film
film placement for premolar film
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For slides 7 through 15, identify the buccal or
lingual location of the structures indicated.
Enter answers on the answer sheet provided.
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incisor film
7
premolar film
The maxillary right lateral incisor is tilted out
of position. In which direction (buccal or
lingual) is it tipped?
33
8
incisor film
canine film
The maxillary left canine is impacted. Is it
located more to the buccal or the lingual?
34
premolar periapical film
9
The amalgam restoration indicated by the arrow is
located on the buccal or the lingual?
premolar bitewing film
35
premolar bitewing film
10
The mandibular second premolar is tilted out of
position. In which direction (buccal or lingual)
is it tipped?
premolar periapical film
36
molar bitewing film
11
The arrow points to a retention pin. Is the pin
located in the buccal or lingual portion of the
tooth?
molar periapical film
37
12
premolar film
molar film
Does the arrow point to the mesiobuccal or
mesiolingual canal?
38
molar bitewing film
13
The amalgam particle indicated by the arrows is
located bucally or lingually?
molar periapical film
39
14
premolar bitewing film
Is the restoration indicated by the red arrows
located on the buccal or lingual of the first
premolar?
canine periapical film
premolar periapical film
40
15
premolar film
incisor film
canine film
The gutta percha root canal filling identified by
the red arrows is located in which canal?