Locate the Object: February 2015 – 12 ANSWER

Now for the answers from today’s earlier post.

Where is the impacted maxillary left canine (orange arrow) in relation to the maxillary left lateral 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).

image shift 9-2


The first thing to do is pick a stationary object that is seen on both radiographs and appears to move in comparison to the impacted maxillary left canine (#11). On these radiographs, we will use maxillary left lateral incisor (#10).

The most obvious angle change is the horizontal angle between the two radiographs. Starting with the maxillary central incisors periapical radiograph and moving to the maxillary left canine periapical radiograph, the horizontal angle increases meaning the source of radiation (tubehead) moves posteriorly. According to point 1 above, this means the images move anterior.

Looking at the second radiograph (maxillary left canine periapical radiograph), we need to compare the image movement of the canine (#11) versus the lateral incisor (#10) to see which object moved more anterior following point 2 listed above.

The lateral incisor (#10) appears to be more anterior on the maxillary left canine periapical radiograph meaning it is farther from the image receptor compared to the canine (#11).

This gives us an answer of the canine (#11) being to the lingual/palatal of the lateral incisor (#10).

SLOB (Same-Lingual, Opposite-Buccal)

We will use the same objects as above (unknown object = impacted maxillary left canine (#11) and fixed object = maxillary left lateral incisor (#10)).

Next, we need to determine which direction we are moving from the maxillary central incisors periapical radiograph to the maxillary left canine periapical radiograph and the answer would be – distal.

On the maxillary left canine periapical radiograph determine what direction does the canine (#11) appear to have moved in relation to the lateral incisor (#10) – distal.

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 canine (#11) is to the lingual of the lateral incisor (#10).

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

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