Dr. Ghassan Ali Object Localization



Download 16.6 Kb.
Date conversion21.11.2016
Size16.6 Kb.
Dr. Ghassan Ali

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, ’s rule):


Utilizes two films with different horizontal or vertical
angulations.

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 (), (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.
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 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 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.

Horizontal movement
If the buccal and lingual 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.
When the tubehead is moved distally and the beam is directed mesially. On the radiograph, the buccal object of interest moves mesially (opposite to tubehead movement and the lingual object of interest moves distally (same direction as tubehead).
When the tubehead is moved mesially and the beam is directed distally. On the radiograph, the buccal object of interest moves distally (opposite to tubehead movement) and the lingual object of interest moves mesially (same direction as tubehead.

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).

Vertical movement
If the buccal and lingual 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.
when the tubehead is moved upward and the beam is directed downward. On the radiograph, the buccal object of interest moves down (opposite to tubehead movement) and the lingual object of interest moves up (same direction as tubehead).
When the tubehead is moved downward and the beam is directed upward. On the radiograph, the buccal object of interest moves up (opposite to tubehead movement) and the lingual object of interest moves down (same direction as tubehead).

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.


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.


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 ’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.


The database is protected by copyright ©dentisty.org 2016
send message

    Main page