What’s the percentage of the presence of an MB2?


Nope. MB2s are EVERYWHERE.

If you only learn one thing today, learn this: The missed MB2 is the number one reason why I see root canals fail.

And honestly, the MB root of the maxillary molar is the number one root that I see failing.

Let’s Get Real About the MB2.

It’s time for some tough love. I honestly don’t think that it’s fair to say that “the root canal failed.” I mean, if the canals were found, cleaned, and shaped properly, then it wouldn’t fail, right? It shouldn’t.

And that my friends, is why we have a silly movie like Root Cause that has given endodontics a bad name.

It all comes down to good endo versus bad endo. If you miss this canal, you are just going to add fuel to their mission to discredit the values of keeping natural teeth, because that root canal is going to fail, and their team gets another point. So, leave your ego at the door and remember what is best for your patient, and now, what is best for your profession as a dentist.  

Yes, the MB2 Is Tough to Find.

I admit it. These canals are hard to find. Even for me, and I’ve been doing this for over a decade!

My advice when it comes to treating the maxillary molar is not perform treatment on them until you have mastered all the other teeth. This is the LAST tooth that you should try. And if you can, do it with a microscope. It will change your life, and your success rate.

Remember that the MB2s exist not only in the first molar, but they also exist in the second molar. Can you tell me the published percentages? Do you remember?

The research shows that the MB2 is present in the maxillary first molar 96.1% of the time, so to me that means 100% of the time. 

In the second maxillary molar the MB2 is present a little less than that, but the percentage is still pretty high. It can be anywhere from 70-93%.  That’s still pretty high don’t ya think?

A Quick MB2 Tooth Story

Here is a case where I found a typical MB2 in the second molar. Tooth #2 was initially symptomatic, but was necrotic upon access and had no tenderness to percussion. Her diagnosis was Necrotic Pulp and Asymptomatic Apical Periodontitis. Some might argue that her pain was from tooth #3 since there is a PARL around the MB root. Well, she does have a missed MB2 in that root, but she is having no pain at all coming from it. That’s next on the treatment plan.

And here is the final product after the root canal treatment…


Remember that the MB2 canal is located a few millimeters lingual to the main MB canal. And sometimes it’s located a bit more into the mesial wall, almost right at that line angle. It can also be located more apical to the MB orifice as well.

So, just because you don’t “see” it doesn’t mean that it isn’t there.

Trust me, I learned this by getting burned myself. I have missed canals in the past because I simply didn’t “see” it. All together now: “That doesn’t mean that it isn’t there! ” 


  1. MB2s are everywhere!  If you aren’t finding them then refer your patient out!  Don’t forget your endodontist is always there to help you when you need it.  
  2. Maxillary first molars have an MB2 pretty much all the time.
  3. Maxillary second molars have an MB2 most of the time, around 85%. Whoa that’s still pretty high!
  4. Know your percentages of canals for all teeth.



Click to check out my article on an MB2 case study:
“Tooth Story #9: MB2 Problems, The Struggle is Real”


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