Locate the Object: August 2013 Answer 2


Now onto the answers for the August 2013 Locate the Object. I will be going over both image shift and SLOB (Same-Lingual, Opposite-Buccal) to determine the location of the left lateral incisor in relation to the left central incisor.

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).
locate the object august 2013 - 1

canine/lateral incisor periapical radiograph

locate the object august 2013 - 2

central incisors periapical radiograph

The first thing to do is pick a stationary object that is seen on both radiographs and appears to move in comparison to the lateral incisor.  On these radiographs, I am using the left central incisor. The most obvious angle change is to the horizontal angle so will we use those changes. Starting with the canine/lateral incisor periapical radiograph and moving to the central incisors periapical radiograph, the source of radiation (tubehead) moves anteriorly decreasing the horizontal angle.

lto july 2013 image shift animation - 1

According to point 1 above, this means the images move posterior.

Looking at the second radiograph (central incisors periapical radiograph), we need to compare the image movement of the left central incisor versus to the left lateral incisor to see which object moved more posterior following point 2 listed above.

The left lateral incisor appears to be more posterior on the radiograph meaning it is farther from the image receptor compared to the left central incisor. This gives us an answer of the left lateral incisor being to the buccal/facial of the left central incisor.

SLOB (Same-Lingual, Opposite-Buccal)

central incisors periapical radiograph

central incisors periapical radiograph

canine/lateral incisor periapical radiograph

canine/lateral incisor periapical radiograph

The first thing to do is again pick an object with a known fixed location – the left central incisor.

The second thing to do is determine which direction we are moving from the central incisors periapical radiograph to the canine/lateral incisor periapical radiograph and the answer would be – distal.

Lastly, on the canine/lateral incisor periapical radiograph determine what direction the left lateral incisor appears to have moved in relation to the left central incisor – mesial. Here is where the acronym comes into play. Did the unknown object move in the SAME direction as the radiographs or in the OPPOSITE direction? Our answer is – opposite and the acronym states that opposite is buccal, so the left lateral incisor is to the buccal of the left central incisor.

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



Leave a comment

Your email address will not be published. Required fields are marked *

2 thoughts on “Locate the Object: August 2013 Answer