A 15-year-old female was referred to an oral surgeon for extraction of an impacted tooth 23, which is located in area apical to teeth 22 and 24, which was found on routine X-rays. How would the oral surgeon decide as to where the impacted tooth lay with respect to being either buccal or palatal to teeth 22 and 24?
The application of this principle can be easily remembered by the acronym SLOB: same lingual, opposite buccal. Thus, if the object in question appears to move in the same direction with respect to the reference structures as does the X-ray tube, it is on the lingual aspect of the reference object; if it appears to move in the opposite direction as the X-ray tube, it is on the buccal aspect. If it does not move with respect to the reference object, it lies at the same depth (in the same vertical plane) as the reference object. The application of this method works equally well when the X-ray tube is moved vertically, instead of horizontally. In this case, the movement of the object’s image in the vertical plane (superior or inferior to the reference structure) is evaluated.
 
Reference: ORAL RADIOLOGY PRINCIPLES AND INTERPRETATION,8th EDITION, Stuart C. White, Michael J. Pharoah
Waters view
Use of panoramic radiograph
Application of the SLOB rule
Lateral head radiograph