What radiographic rule helps determine buccal-lingual position of a root when two images are taken at different angles?

• A. FOL rule.
• B. SLOB rule (Same Lingual, Opposite Buccal).
• C. SOL rule.
• D. LOG rule.

Answer: (B)

When you take two radiographs from different angles, you can use parallax to pinpoint where a root sits in relation to the cheek and tongue. The rule states that the structure located toward the tongue (lingual) will appear to move in the same direction as the change in the x-ray beam, while the structure toward the cheek (buccal) will move in the opposite direction. So, by comparing how the root image shifts between the two angled exposures, you can determine its buccal-lingual position: same direction indicates lingual, opposite direction indicates buccal. This approach leverages how parallax reveals depth on two-dimensional images, making it the reliable method for localizing the root in the buccal-lingual dimension. Other named rules don’t describe this specific relationship between angle change and image movement, so they don’t provide the same diagnostic guidance.