Object Localization - Dental Radiology - Lecture Slides, Slides of Dental Radiology

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The following slides describe

Object Localization, including the

Right Angle Technique and the

Tube Shift Technique.

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

Object Localization

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.

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.

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).

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

distal mesial

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.

distal mesial

mesial

distal

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 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).

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.

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.