Here is the answer for the September 2014 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
- 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 supernumerary tooth. On these radiographs, we will use the left central incisor (#9). The most obvious angle change is the horizontal angle. Starting with the right lateral incisor/central incisor periapical radiograph and moving to the left central incisor/lateral incisor 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 (left central incisor/lateral incisor periapical radiograph), we need to compare the image movement of the supernumerary radiograph versus the left central incisor (#9) to see which object moved more anterior following point 2 listed above.
The left central incisor (#9) appears to be more anterior on the left central incisor/lateral incisor periapical radiograph meaning it is farther from the image receptor compared to the supernumerary tooth. This gives us an answer of the supernumerary tooth being to the lingual/palatal of the left central incisor (#9).
SLOB (Same-Lingual, Opposite-Buccal)
The first thing to do is again pick an object with a known fixed location – the left central incisor (#9).
The second thing to do is determine which direction we are moving from the right lateral incisor/central incisor periapical radiograph to the left central incisor/lateral incisor periapical radiograph and the answer would be – distal.
Lastly, on the left central incisor/lateral incisor periapical radiograph determine what direction the supernumerary tooth appears to have moved in relation to the left central incisor (#9) – 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 supernumerary tooth is to the lingual of the left central incisor (#9).
Another case will be coming next month. If you have any questions or comments, please let me know below. Thanks and enjoy!
