Today I will be going over another way to determine the location of an object (known or unknown) that appears on intraoral radiographs. One important note – do not combine the two methods, use only the image shift or the SLOB rule when locating an object.
The SLOB (same-lingual, opposite-buccal) rule is similar to image shift but the film/sensor must be positioned to the lingual of the teeth to use this method. This will make any object that is buccal/facial of the teeth automatically farther from the film/sensor. The SLOB rule can be used with vertical angle changes; however it is primarily used with horizontal angle changes. Instead of referring to changes with the specific horizontal angle, the images are described in mesial (shows more mesial or anterior objects) or distal (shows more distal or posterior objects) terms. For example, using two radiographs, a premolar periapical radiograph and a molar periapical radiograph, the premolar periapical radiograph would be to the mesial and the molar periapical radiograph would be to the distal. Below is an example with a tiny supernumerary tooth in the mandible and the steps used for this rule.
2) You must select two things that are visible on both images – 1) a fixed or known object (mandibular first premolar) and 2) the unknown object (supernumerary tooth labeled A).
3) Now determine which direction the images appear to move from image 1 to image 2 – mesial or anterior.
4) Next determine where the image of the unknown object (label A) moves in relation to the fixed object (mandibular first premolar) from image 1 to image 2 – the supernumerary tooth moves more mesial or anterior than the mandibular first premolar.
5) Using the SLOB rule (same-lingual, opposite-buccal) this shows that the unknown object image moves in the SAME direction as the images (1 to 2) and therefore it is to the lingual of the mandibular first premolar.
This is something that takes practice to get the hang of. I hope these last two posts have broken them down to help refresh or inform you how to use them.
Should you have any questions or thoughts on this topic, please let me know.
Thanks and enjoy!