# Locate the Object: November 2013 Answer – Image Shift

Now onto the answers for the November 2013 Locate the Object. Here is image shift for both cases with the SLOB (Same-Lingual, Opposite-Buccal) coming later today.

Image shift

Before starting to use the image shift principle it is important to know/remember two key points

1. Images move in the opposite direction from the movement of the source.
2. Images of objects farther from the image receptor will move more (aka objects (images) more facial/buccal will appear to move more).

1) Pick a stationary object that is seen on both radiographs and appears to move in comparison to the unknown radiopaque entity (A) = second premolar.

2) Determine the obvious angle change = horizontal angle. (Starting with the premolar periapical radiograph and moving to the molar periapical radiograph, the source of radiation (tubehead) moves posteriorly/distal increasing the horizontal angle. According to point 1 above, this means the images move anterior/mesial.)

3) Determine the image movement of the unknown object (radiopaque entity labeled A) versus the stationary object (second premolar) = more anterior/mesial (when moving from the premolar periapical to the molar periapical radiograph).

4) The radiopaque entity (A) appears to be more anterior/mesial on the radiograph meaning it is farther from the image receptor compared to the second premolar. This gives us an answer of the radiopaque entity (A) being to the buccal/facial of the second premolar.

1) Pick a stationary object that is seen on both radiographs and appears to move in comparison to the supernumerary tooth (A) = first premolar.

2) Determine the obvious angle change = horizontal angle. (Starting with the premolar periapical radiograph and moving to the canine periapical radiograph, the source of radiation (tubehead) moves anteriorly/mesial decreasing the horizontal angle. According to point 1 above, this means the images move posterior/distal.)

3) Determine the image movement of the supernumerary tooth (A) versus the stationary object (first premolar) = more anterior/mesial (when moving from the premolar periapical to the canine periapical radiograph).

4) The supernumerary tooth (A) appears to be move more anterior/mesial on the radiograph meaning it is closer from the image receptor compared to the second premolar. This gives us an answer of the supernumerary tooth (A) being to the lingual of the first premolar.

Another case will be coming next month, December 10th. If you have any questions or comments, please leave them below. Thanks and enjoy!