Now for the answers from today’s earlier post.
Where is the radiopaque restoration on the mandibular right first premolar crown (orange arrow) in relation to the root canal space?
Before starting to use the image shift principle it is important to know/remember two key points
- Images move in the opposite direction from the movement of the source.
- Images of objects farther from the image receptor will move more (aka objects (images) more facial/buccal will appear to move more).
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 mandibular right first premolar (#28). On these radiographs, we will use the root canal space of the mandibular right first premolar (#28).
The most obvious angle change is the horizontal angle between the two radiographs. Starting with the mandibular right premolar periapical radiograph and moving to the mandibular right canine 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 right canine periapical radiograph), we need to compare the image movement of the radiopaque restoration (#28) versus the root canal space (#28) to see which object moved more posterior following point 2 listed above.
The radiopaque restoration (#28) appears to be more posterior on the mandibular right canine periapical radiograph meaning it is farther from the image receptor compared to the root canal space (#28).
This gives us an answer of the radiopaque restoration on the mandibular right first premolar (#28) being to the buccal/facial of the root canal space of the mandibular right first premolar (#28).
SLOB (Same-Lingual, Opposite-Buccal)
We will use the same objects as above (unknown object = radiopaque restoration (#28) and fixed object = root canal space (#28)).
Next, we need to determine which direction we are moving from the mandibular right premolar periapical radiograph to the mandibular right canine periapical radiograph and the answer would be – mesial.
On the mandibular right canine periapical radiograph determine what direction does the radiopaque restoration (#28) appear to have moved in relation to the root canal space (#28) – 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 (#28) is to the buccal of the root canal space (#28).
Another case will be coming next week. If you have any questions or comments, please leave them below. Thanks and enjoy!
