23 July 2017
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Is that 8 close to the IDN? Radiographic signs.

Is that 8 close to the IDN? Radiographic signs.

This article covers one of the favourite questions asked by oral surgery tutors. How can you tell whether that 8 is close to the inferior dental nerve (IDN)? At some point in your undergraduate years you WILL get asked this question but don’t worry, we’re here to help!

So you have a PA or a 1/2 OPT of a partially erupted third molar that has been victim of recurrent pericoronitis (make sure you know your NICE guidelines on wisdom tooth removal before you suggest taking it out to your tutor!), so what do you look for?

Your textbooks will say that there are 4 or 5 signs of close relation between the IDN and the wisdom tooth. Remember, when you’re being asked a question it is best not to say: “There are 5 signs, which are…” and then trying to list them, chances are you’ll forget one in the heat of the moment!

The first thing to look for is the IDN itself, it can be quite difficult to spot but will resemble “tramlines” travelling through the ramus and body of the mandible, that is the inferior dental canal, through which the nerve travels. The bone that houses the canal is slightly more dense, hence the white lines.

Once you can see and follow these lines, you can then start to spot the signs that indicate that the wisdom tooth is intimately related. These are:

Loss or interruption of “Tramlines”

Follow the borders of the ID canal with your finger. Look for any loss of cortication (interruption to the white line), usually found in the superior border.

Narrowing of the tramlines

Check that the distance between the tramlines is continuous throughout and that there aren’t any constrictions.

Sudden change in direction of tramlines

You may see that the course of the IDN actually curves around an 8.

Deviation of the tooth root

Look for any kinks and changes of direction the to root of the 8.

Radiolucent band across the apex of the tooth

Check that the radiopacity of the tooth’s root is consistent, a radiolucent band across the tooth can suggest a close proximity. This could mean the IDN has either created a groove in the root, or is actually going through the middle of the tooth. Equally, it could be the nerve is not in contact but it’s radiolucency is superimposed onto the tooth.

Other things to look for are generally how close the tooth is actually to the nerve! If you can see a nice solid width of bone between the two then that’s good news!