Locate the Object: February 2015 – 9 ANSWER


Now for the answers from today’s earlier post.

Where is the mandibular right central incisor crown (orange arrow) in relation to the mandibular left central incisor crown?

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 3-2

 

The first thing to do is pick a stationary object that is seen on both radiographs and appears to move in comparison to the mandibular right central incisor (#25). On these radiographs, we will use the mandibular left central incisor (#24).

The most obvious angle change is the horizontal angle between the two radiographs. Starting with the mandibular right canine/lateral incisor periapical radiograph and moving to the mandibular central incisors 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 (mandibular central incisors periapical radiograph), we need to compare the image movement of (#25) versus the (#24) to see which object moved more posterior following point 2 listed above.

The tooth (#25) appears to be more posterior on the mandibular central incisors periapical radiograph meaning it is farther from the image receptor compared to (#24).

This gives us an answer of the post of the mandibular right central incisor (#25) being to the buccal/facial of the mandibular left central incisor (#24).

SLOB (Same-Lingual, Opposite-Buccal)

We will use the same objects as above (unknown object = (#25) and fixed object = (#24)).

Next, we need to determine which direction we are moving from the mandibular right canine/lateral incisor periapical radiograph to the mandibular central incisors periapical radiograph and the answer would be – mesial.

On the mandibular central incisors periapical radiograph determine what direction does (#25) appear to have moved in relation to (#24) – 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 mandibular right central incisor (#25) is to the buccal of the mandibular left central incisor (#24).

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

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