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2. 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, Clark’s rule)
Utilizes two films with different horizontal or vertical
angulations

4. Right Angle Technique Right Angle (Occlusal) 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. incisors canine premolar molar
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.

11. 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
distal
mesial

12. 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
distal
mesial

13. 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
distal
mesial

14. Maxillary PA BW Mandibular PA
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.

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. 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).

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. 1
canine film
incisor film
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.
Is the composite restoration on tooth # 8 (arrows) located on the buccal or lingual?

24. 2
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).

25. 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.

26. 3
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.

27. 4
premolar film
molar film
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

28. 5
incisor film
canine film
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.

29. 6
canine film
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?

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

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
incisor film
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 film9
The amalgam restoration indicated by the arrow is located on the buccal or the lingual?
premolar bitewing film

35. premolar bitewing film10
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 Does the arrow point to the mesiobuccal or mesiolingual canal?
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?