Now for the answers from today’s earlier post.
Where is the external resorption (X) in relation to the treated 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 external resorption on the maxillary left central incisor (#9). On these radiographs, we will use the endodontically treated root canal space of the maxillary left central incisor (#9).
The most obvious angle change is the horizontal angle between the two radiographs. Starting with the maxillary left central incisor periapical radiograph and moving to the maxillary left lateral incisor 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 lateral incisor periapical radiograph), we need to compare the image movement of the external resorption versus the endodontically treated root canal space to see which object moved more anterior following point 2 listed above.
The endodontically treated root canal space appears to be more anterior on the maxillary left lateral incisor periapical radiograph meaning it is farther from the image receptor compared to the external resorption.
This gives us an answer of the external resorption of the maxillary left central incisor (#9) being to the lingual/palatal of the endodontically treated root canal space of the maxillary left central incisor (#9).
SLOB (Same-Lingual, Opposite-Buccal)
We will use the same objects as above (unknown object = external resorption of the maxillary left central incisor (#9) and fixed object = endodontically treated root canal space of the maxillary left central incisor (#9)).
Next, we need to determine which direction we are moving from the maxillary left central incisor periapical radiograph to the maxillary left lateral incisor periapical radiograph and the answer would be – distal.
On the maxillary left lateral incisor periapical radiograph determine what direction does the external resorption appear to have moved in relation to the endodontically treated root canal space – 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 external resorption is to the lingual of the endodontically treated root canal space.
Another case will be coming tomorrow. If you have any questions or comments, please leave them below. Thanks and enjoy!