Locate the Object: February 2015 – 1 ANSWER


Now for the answers from today’s earlier post.

Which root is the post (orange arrow) in?

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 3-1

The first thing to do is pick a stationary object that is seen on both radiographs and appears to move in comparison to the post of the maxillary right first premolar (#5). On these radiographs, we will use the other endodontically treated root of the maxillary right first premolar (#5).

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 canine 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 canine periapical radiograph), we need to compare the image movement of the post of the maxillary right first premolar (#5) versus the other endodontically treated root of the maxillary right first premolar (#5) to see which object moved more posterior following point 2 listed above.

The other endodontically treated root of the maxillary right first premolar (#5) appears to be more posterior on the maxillary right canine periapical radiograph meaning it is farther from the image receptor compared to the post of the maxillary right first premolar (#5).

This gives us an answer of the post of the maxillary right first premolar (#5) being to the lingual/palatal of the other endodontically treated root of the maxillary right first premolar (#5).

SLOB (Same-Lingual, Opposite-Buccal)

We will use the same objects as above (unknown object = post of the maxillary right first premolar (#5) and fixed object = other endodontically treated root of the maxillary right first premolar (#5)).

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

On the maxillary right canine periapical radiograph determine what direction does the post of the maxillary right first premolar (#5) appear to have moved in relation to the other endodontically treated root of the maxillary right first premolar (#5) – 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 post of the maxillary right first premolar (#5) is to the lingual of the other endodontically treated root of the maxillary right first premolar (#5).

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