Locate the Object: February 2015 – 15 ANSWER

Now for the answers from today’s earlier post.

Where is the radiopaque restoration (orange arrow) in relation to the occlusal restoration on the maxillary right first molar (#3)?

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).

image shift 1-1


The first thing to do is pick a stationary object that is seen on both radiographs and appears to move in comparison to the round radiopaque restoration on the maxillary right first molar (#3). On these radiographs, we will use the occlusal restoration on the maxillary right first molar (#3).

The next step is to determine what angle change is obvious between the two radiographs? Positive vertical angle, negative vertical angle or horizontal angle.

The most obvious angle change is the horizontal angle between the two radiographs. Starting with the maxillary right molar periapical radiograph and moving to the maxillary right premolar periapical radiograph, the horizontal angle decreases meaning the source of radiation (tubehead) moves anteriorly. According to point 1 above, this means the images move posterior.

Looking at the second radiograph (maxillary right premolar periapical radiograph), we need to compare the image movement of the round radiopaque restoration versus the occlusal restoration to see which object moved more posterior following point 2 listed above.

The occlusal restoration appears to be more posterior on the maxillary right premolar periapical radiograph meaning it is farther from the image receptor compared to the round radiopaque restoration.

This gives us an answer of the round radiopaque restoration being to the lingual/palatal of the occlusal restoration.

SLOB (Same-Lingual, Opposite-Buccal)

We will use the same objects as above (unknown object = round radiopaque restoration on maxillary right first molar (#3) and fixed object = occlusal restoration on maxillary right first molar (#3)).

Next, we need to determine which direction we are moving from the maxillary right molar periapical radiograph to the maxillary right premolar periapical radiograph and the answer would be – mesial.

On the maxillary right premolar periapical radiograph determine what direction does the round radiopaque restoration appear to have moved in relation to the occlusal – 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 – same and the acronym states that same is lingual, so the round radiopaque restoration is to the lingual of the occlusal restoration.

Another case will be coming tomorrow. 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 *

This site uses Akismet to reduce spam. Learn how your comment data is processed.