Locate the Object: October 2014 ANSWER


I did not realize that the answer to the October 2014: Locate the Object was not out so here it is, a bit late. 😐

I’ll be going over both image shift and SLOB (Same-Lingual, Opposite-Buccal). .

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 october 2014 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 impacted canine (#11). On these radiographs, we will use the left lateral incisor (#10). The most obvious angle change is the horizontal angle. Starting with the left central incisor/lateral incisor periapical radiograph and moving to the premolar periapical radiograph, the source of radiation (tubehead) moves posteriorly increasing the horizontal angle.  According to point 1 above, this means the images move anterior.

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

The left lateral incisor (#10) appears to be more anterior on the premolar periapical radiograph meaning it is farther from the image receptor compared to the impacted canine (#11). This gives us an answer of the impacted canine (#11) being to the lingual/palatal of the left lateral incisor (#10).

SLOB (Same-Lingual, Opposite-Buccal)

The first thing to do is again pick an object with a known fixed location – the left lateral incisor (#10).

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

Lastly, on the premolar periapical radiograph determine what direction does the impacted canine (#11) appear to have moved in relation to the left 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 impacted canine (#11) is to the lingual of the left lateral incisor (#10).

Another case will be coming next month. If you have any questions or comments, please let me know below. Thanks and enjoy!

Leave a Reply