I talk about missed MB2s all the time (“MB2 Problems, The Struggle is Real” and “MB2s are Everywhere,” to name a few other posts), but it’s not the only commonly-missed canal. In many ways, the second distal canal is the sister to the MB2.

Here is a classic case of the misses:

This patient had a previously-treated tooth with tenderness to percussion and normal probings. The diagnosis is Previously Treated Tooth with Symptomatic Apical Periodontitis. From the preoperative radiograph, you can see that the distal canal is not quite 100% centered.

On the bitewing, you can appreciate the potential for a missed canal by the radiolucent “line” adjacent to the distal gutta percha. And from the look of it, I may not love the root canal on #14 either — or the distal margin of the crown on #19.

Of course, I’ve learned from experience that I cannot tell the whole tooth story from just the clinical exam or the 2D radiographs. So I put my handy dandy cone beam to work. (I LOVE my cone beam!)

Here is the axial shot. You can’t see the missed canal outright, but you can see that the existing gutta percha is not centered in the canal. There is definitely room for another canal in there!

It’s so important to get a clear idea of the lay of the land. Getting the “map” of the canals preoperatively helps me understand the tooth. Once I do, I know exactly where to go once I access. 

In the end, I found the second distal canal and completed the case.

When you are treating mandibular molars, my advice is that you always look for a second distal canal. 

And if it’s a large elliptical canal, make sure you instrument that canal as if it is two canals: a DB and a DL canal. Sometimes these bad boys won’t split until closer to the apex. They can be really hard to see, so make sure that you are using magnification every time. 

Now go save some teeth!

-Sonia

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