Ah, the infamous MB2. I feel like it’s the one thing in endo that every dentist wants to master—but how often are we given the chance to practice? Every time I ask people what their endo goals are, they say: “I want to know how to locate the MB2 canal and treat it successfully.” Seriously. Like every. single. time.

But, there are some ugly truths to the MB2 in endodontics, and I am going to unleash them here so you can manage your expectations. 

It’s Not Just About How to Locate the MB2 Canal, It’s Knowing How Often It’s Necessary

The first problem I see is that people either don’t remember or weren’t taught how often the MB2 actually exists. Here’s the short answer…it’s pretty much always there. Let’s just say you should find it 100% of the time. This surprises SO many dentists. Does it surprise you?

Here’s some evidence from recent studies that support what I’m saying here:

“The first maxillary molar teeth exhibited the highest prevalence of MB2 canals 92% of the time.  The second maxillary molar teeth showed a lower prevalence of MB2 canals 69% of the time.” 

Probably the most-quoted article I can remember from residency was the one by Kulid and Peters where they found this: 

“A second ML canal was located in the coronal half of 95.2% of the MB roots.”

I think it’s important to share this information. I say this because I have gotten in really heated arguments with some dentists about this. Trust me, those conversations got ugly, but the truth is that the MB2 exists more often than most people think—supporting the importance of the MB2 in endodontics as a priority for instruction and mastery.

Finding the MB2 Successfully

So it is one thing to know the incidence of the MB2—let’s agree that’s around 90-95% of the time here to simplify things. That’s the first critical piece of knowledge. 

But, step two is to know where they are once you get inside the tooth. 

Yes, it’s true that the MB2 is usually lingual to the MB1, but sometimes it can also be mesio-lingual, so that it almost seems like it sits in the mesial wall. Most of the time, the orifice actually begins more apical than where the MB1 starts. As such, you need to remove dentin selectively in order to find it. 

This is probably the hardest thing I can teach someone. Why? Because you really need some heavy magnification to see this, and it requires a high degree of precision. Unfortunately, you probably need to fail a few times (AKA perforate or miss the canal) until you get it. Let’s be real here—learning how to locate the MB2 consistently requires awareness and practice. Without someone knowledgeable guiding you while you do it, it can be really difficult to learn! 

That’s one of the reasons why I created E-School LIVE. Because I knew I had to create something that gave people the opportunity to learn while I watched them in-person. That peer-to-peer work is vital—because nobody taught me what I am about to teach you right now. I had to learn it on my own, by making mistakes. 

I don’t say that to make you feel bad—MB2 in endodontics is tough stuff. But I want to stress the importance of practice and making the attempt (while equipped with lots of knowledge, of course).

Understanding the MB2 In Endodontics Is a Process

You need to practice over and over to really get the hang of it. It didn’t even click while I was an endodontic resident. I honestly don’t think I actually had a proper understanding of the MB2 until I was three years into owning my practice.

This is essential, and it took me a while to figure out, but sometimes canals start as GROOVES. So I instrument grooves to find canals.  

Let me say that one more time… You should be instrumenting grooves and canals.

So let’s recap:

  • Step one is assuming the MB2 canal is there every time.
  • Step two is knowing where to go once inside the tooth.
  • Step three is knowing how to instrument the canals once you find them.

That’s a whole other topic in and of itself, and getting down any canal is something that I prioritize in E-School with Coaching content because it’s super dynamic and takes a lot of time, skill, and patience to really understand. 

But I swear, once you get it, you can apply it to any canal, anytime. Even the MB2. It’s really all about knowing how to find the MB2 (and realizing it’s there in the first place). Once you’ve got it located, you just apply typical endo concepts and—voilá—that’s another success in the books!

An MB2 Tooth Story

One of my favorite patients of all time discovered my blog and drove all the way from Florida to North Carolina so I could do her root canal (retreatment actually).  

Now, there’s a lot going on in her case (images to follow), but for the purposes of this blog, we will be focusing on tooth #15 only. 

She’d seen her local dentist and endodontist (who did the original root canal) and they wanted to take out tooth #15 because they said that it was cracked. Oof, there is that silly diagnosis again! 

Despite what they had told her, she was adamant on saving her tooth, so she did her own research. And let me tell you, did she EVER. I have never met a patient who was a better advocate for their own health. She amazed me with her questions and she had a deep grasp of what was happening to her body.  

Check out her preoperative radiographs…

And her CBCT. That lesion is SO much bigger on the CBCT right?  

Here are the buccal canals….

And her palatal root…

The axial slice shows a very broad MB root that connects to the palatal root. I find this type of anatomy very tricky sometimes. But I think you can see that there is definitely room for an MB2 in that root.

Here is an axial slice that is a bit more apical …

The patient and I had a very detailed discussion about all of her treatment. I thought to myself that if there was an MB2 in 15, it probably was a hard one to find since the previous endodontist wasn’t able to discover it. So, I informed her during the evaluation that I may also not be able to find it and she may still need an extraction. She understood, but she still wanted me to give it a try.

This was the coronal view of the CBCT…

The tooth had no pain at the time of the evaluation, there was no pain to percussion or palpation, and there were no abnormal probings. The diagnosis for this tooth was Previously Treated and Asymptomatic Apical Periodontitis #15.  

I accessed the tooth knowing I had to look for an MB2, because, after all, that’s step one that I listed above, right? And then step two—I had to know where to find it. And there it was, a groove! I knew I had to instrument it. Once I did, it opened up beautifully into another canal!

I’m not at all surprised that it had its own portal of exit. That’s why the lesion is so big—not because it’s cracked. 

Here is my final obturation…

We also took a postoperative CBCT and you can see where the MB2 was located in that root. Here is the coronal slice in the axial view for another angle… 

And here is a more apical slice in the MB root (also notice in the preoperative CBCT that you didn’t actually see the canal in the CBCT).

And here is the postoperative coronal view…

Looking to the Future

Now it is just a matter of time to see how (and if) this tooth heals. I’ll be seeing this wonderful patient in about six months to take a look at how things have been progressing. And I personally can’t wait to find out.

I hope these simple, actionable steps give you some insight on considering the MB2 canal in endodontics and how to find and treat that tricky—infamous even!—canal. 

And if you want even more actionable insight and guidance when it comes to treating the trickiest of cases, check out E-School with Coaching for more endo goodness! 

– Sonia