Locate the Object: June 2015 – ANSWER 2

Now for the answers from Tuesday.

Where is the root of the mandibular left lateral incisor root (#23) in relation to the root of the mandibular left central incisor (#24)?

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).

The first thing to do is pick a stationary object that is seen on both radiographs and appears to move in comparison to the lateral incisor root (#23). On these radiographs, we will use the central incisor root (#24).

The next step is to determine what angle change is obvious between the two radiographs? Positive vertical angle, negative vertical angle or horizontal angle.

The most obvious angle change is the horizontal angle between the two radiographs. Starting with the mandibular left central incisor/lateral incisor periapical radiograph and moving to the mandibular left canine/first premolar 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 (mandibular left canine/first premolar periapical radiograph), we need to compare the image movement of the lateral incisor root (#23) versus the central incisor root (#24) to see which object moved more anterior following point 2 listed above.

The central incisor root (#21) appears to be more anterior on the mandibular left canine/first premolar periapical radiograph meaning it is farther from the image receptor compared to the lateral incisor root (#23).

This gives us an answer of the lateral incisor root (#23) being to the lingual of the central incisor root (#24).

SLOB (Same-Lingual, Opposite-Buccal)

We will use the same objects as above (unknown object = lateral incisor root (#23) and fixed object = central incisor root (#24)).

Next, we need to determine which direction we are moving from the mandibular left central incisor/lateral incisor periapical radiograph to the mandibular left canine/first premolar periapical radiograph and the answer would be – distal.

On the mandibular left canine/first premolar periapical radiograph determine what direction does the lateral incisor root (#23) appear to have moved in relation to the central incisor root (#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 – same and the acronym states that same is lingual, so the lateral incisor root (#23) is to the lingual of central incisor root (#24).

If you have any questions or comments, please leave them below. Thanks and enjoy!