Locate the Object: July 2015 – ANSWER

Now the answers from yesterday.

Where is the restoration on the maxillary left first molar (#14)?

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 july 2015 drgstoothpix

The first thing to do is pick a stationary object that is seen on both radiographs and appears to move in comparison to the restoration. On these radiographs, we will use the pulp chamber of the maxillary left first molar (#14).

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 left premolar periapical radiograph and moving to the maxillary left molar 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 premolar periapical radiograph), we need to compare the image movement of the restoration versus the pulp chamber (#14) to see which object moved more anterior following point 2 listed above.

The restoration appears to be more anterior on the maxillary left premolar periapical radiograph meaning it is farther from the image receptor compared to the pulp chamber (#14).

This gives us an answer of the restoration being to the facial of the pulp chamber (#14).

SLOB (Same-Lingual, Opposite-Buccal)

We will use the same objects as above (unknown object = restoration and fixed object = pulp chamber (#14)).

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

On the maxillary left molar periapical radiograph determine what direction does the restoration appear to have moved in relation to the pulp chamber (#14) – 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 restoration is to the buccal of  the pulp chamber  (#14).

If you have any questions or comments, please leave them below. Thanks and enjoy!

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