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 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

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.

Tube-Shift Localization (Clark)

SLOB RuleSame 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.

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.

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).

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.

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).

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.

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

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

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

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).

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

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

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

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).

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

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).

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.

On the following slides, identify the buccal or lingual location of the selected objects. When you click the mouse, the correct response and a brief explanation will appear.

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.

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).

PIDPID

lingualbuccal

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.

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

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.

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.

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).

film placement for canine film film placement for premolar film

PID placement for premolar film

PID placement for canine film

root tip

7

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

premolar film incisor film

The tubehead moves mesially from the premolar film to the incisor film. The lateral incisor also moves mesially, starting out overlying the canine on the premolar film and ending up over the central incisor on the incisor film. Since the lateral moves the same direction as the tubehead, it is tipped lingually.

incisor film canine film8

The maxillary left canine (arrow) is impacted. Is it located more to the buccal or the lingual?

The tubehead moves distally from the incisor film to the canine film. The impacted canine also moves distally, starting out overlying # 9 on the incisor film and ending up over the lateral incisor on the canine film. The impacted tooth is located on the lingual (palatal).

premolar bitewing film

9

The amalgam restoration indicated by the arrow is located on the buccal or the lingual?

premolar periapical film

The tubehead moves down from the premolar periapical film to the bitewing film. The restoration also moves down, starting out above the two occlusal restorations on the periapical film and ending up overlapping the occlusal restorations on the bitewing film. The restoration is located on the lingual.

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?

The tubehead moves down from the premolar bitewing film to the periapical film. The second premolar also moves down, indicating that it is lingually tipped.

molar bitewing film

molar periapical film

11

The tubehead moves down from the molar bitewing film to the periapical film. The pin identified by the arrows also moves downward. Since the movement of the pin follows the direction the tubehead was moved, it is located toward the lingual aspect of the tooth. The other pin is located toward the buccal, since it moved upward as the tubehead moved down.

The arrows point to a retention pin. Is the pin located in the buccal or lingual portion of the tooth?

premolar film molar film

12

Does the arrow point to the mesiobuccal or mesiolingual canal?

The tubehead moves distally from the premolar film to the molar film. The canal indicated by the arrow also moves distally to align with the other canal, which moves mesially (The canals have to move in opposite directions in order to be superimposed on each other). The indicated canal (arrow) is located mesiolingually.

molar bitewing film

molar periapical film

13

The amalgam particle indicated by the arrows is located bucally or lingually?

The tubehead moves down from the bitewing film to the mandibular periapical film. The amalgam particle moves upward (opposite direction), indicating that it is located buccally.

The tubehead moves distally from the canine film to the premolar periapical. The restoration moves mesially. From the bitewing to the mandibular premolar periapical, the tubehead moves down and the restoration moves up. The restoration is located on the buccal of # 21.

canine periapical film

premolar periapical film

premolar bitewing film14

Is the restoration indicated by the arrows located on the buccal or lingual of the first premolar?

15

incisor film canine film

premolar film

The gutta percha root canal filling identified by the arrows is located in which canal? In moving from the incisor film to the canine film, and then from the canine film to the premolar film, the tubehead moves distally. The gutta percha (arrows) also moves distally in each case. Therefore, it is in the lingual canal.

This concludes the section on Object Localization. Additional self-study modules are available at: http://dent.osu.edu/radiology/resources.php

If you have any questions, you may e-mail me at jaynes.1@osu.edu.

Robert M. Jaynes, DDS, MSDirector, Radiology GroupCollege of DentistryOhio State University