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SLOB Rule — MFDS Part 1 MCQ

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ModerateRadiologySLOB RuleMFDS Part 1

An unerupted maxillary canine is superimposed on the lateral incisor root on a periapical radiograph. A second periapical radiograph is taken with a horizontal shift of the X-ray tube head. What is the principal purpose of applying the SLOB rule to these two images?

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Correct answer: B — Determine the bucco-palatal position of the canine relative to the adjacent teeth

The correct answer is B. The SLOB rule is a parallax method used to determine the bucco-lingual or, in the maxilla, bucco-palatal position of a structure that is superimposed on adjacent anatomy. Two projections are obtained with different tube-head positions. If the structure's image moves in the same direction as the tube shift, it lies lingually or palatally; movement in the opposite direction indicates a buccal position. Parallax does not itself diagnose external root resorption, although the radiographs should also be examined for this complication. Root development and mesiodistal angulation can be assessed radiographically without applying the SLOB relationship. Radiation dose is determined from exposure and equipment parameters, not image displacement.

Reference: Faculty of Dental Surgery, Royal College of Surgeons of England. Management of the Palatally Ectopic Maxillary Canine, section 'Radiographic examination', 2022 (revised January 2023). https://www.rcseng.ac.uk/-/media/Files/RCS/FDS/Guidelines/Management-of-the-Palatally-Ectopic-Maxillary-Canine--revised-with-edits-25-Jan-2023.pdf