Root Canal Treatment of a Mandibular Molar (The Other MB2: The Second Distal Canal)

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. Buckle up, because in today’s post, we’re going to dive into a root canal treatment of a mandibular molar.

No dilly-dallying. Let’s jump right in.

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, we see the distal canal isn’t 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 the whole tooth story doesn’t come from just the clinical exam or the 2D radiographs.

So, I put my handy dandy cone beam to work. This bit of technology uses cone beam computerized tomography (CBCT) to help me detect and diagnose the etiology of root canal failures, as well as determine lesion size and find hard-to-spot canals… especially in the MB2 and maxillary molars. 

For me personally, I find that the coronal view is the most helpful application of this tool. 

Why? Because it will show you exactly what the canal morphology looks like. And that knowledge will you give you a whole heck of a lot more insight into what is going on with the internal anatomy of a tooth before you dive in and start doing a root canal. 

If you’re doing a lot of root canals in your practice, it is definitely worth seeing if a cone beam is in your budget. I find it super useful.

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

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 as well as a middle mesial canal off shoot and completed the case.

What’s your takeaway for root canal treatment of mandibular molars?

When you are treating mandibular molars, my advice is that you always look for a second distal canal because it is present more than HALF of the time. This is a critical step to ensure a totally successful outcome. 

And if it’s a large elliptical canal, make sure you instrument that canal as if it’s two canals: a DB and a DL canal. Sometimes these bad boys won’t split until closer to the apex. So, take your rotary against both the buccal wall and the lingual wall separately, and you just might get into that split.  They can be really hard to see, so make sure you’re using magnification every time.

Honestly, you should just assume the second distal canal is hiding in there somewhere, and get serious about your imaging to see if you can find it. 

I hope this play-by-play (or tooth-by-tooth?) look at one tricky case was useful to you. Now get out there and go save some teeth!

– Sonia