Locate the Object: July 2014 (b) ANSWER


Here is the answer for the July 2014 (b) Locate the Object. We will 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 - July 2014 b

The first thing to do is pick a stationary object that is seen on both radiographs and appears to move in comparison to the radiopaque restoration on the maxillary right second premolar (#4).  On these radiographs, we will use the root canal space of the maxillary right second premolar (#4). The most obvious angle change is the horizontal angle. Starting with the molar bitewing radiograph and moving to the premolar bitewing radiograph, the source of radiation (tubehead) moves anteriorly decreasing the horizontal angle.  According to point 1 above, this means the images move posterior.

Looking at the second radiograph (premolar bitewing radiograph), we need to compare the image movement of the radiopaque restoration on the maxillary right second premolar (#4) versus the root canal space of the maxillary right second premolar (#4) to see which object moved more posterior following point 2 listed above.

The radiopaque restoration on the maxillary right second premolar (#4) appears to be more posterior on the premolar bitewing radiograph meaning it is farther from the image receptor compared to the root canal space of the maxillary right second premolar (#4). This gives us an answer of the radiopaque restoration on the maxillary right second premolar (#4) being on the buccal/facial surface of the maxillary right second premolar (#4).

SLOB (Same-Lingual, Opposite-Buccal)

The first thing to do is again pick an object with a known fixed location – the root canal space of the maxillary right second premolar (#4).

The second thing to do is determine which direction we are moving from the molar bitewing radiograph to the premolar bitewing radiograph and the answer would be – mesial.

Lastly, on the premolar bitewing radiograph determine what direction the radiopaque restoration on the maxillary right second premolar (#4) appears to have moved in relation to the root canal space of the maxillary right second premolar (#4) – 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 – opposite and the acronym states that opposite is buccal, so the radiopaque restoration on the maxillary right second premolar (#4) is on the buccal surface of the maxillary right second premolar (#4).

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

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