I am going to assume that you know this already, but this is such an important fact to emphasize — MB2s are everywhere.

Through my time teaching, I still can’t believe that many dentists don’t know the true percentages of the presence of MB2s.

When I ask my residents, they say “Ummmm….50%??”
And I say, “Ummm, NO.”

They can see the look of disappointment on my face.  I hope that if they learn nothing else that day, that they learn at least this ONE thing: The missed MB2 is the number one reason why I see root canals fail.

And I would say that the MB root of the maxillary molar is the number one root that I see failing.   Let me back up — I don’t think that it’s fair to say that “the root canal failed”. I think we need to say that “the operator 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 started to make its way through the streaming universe, giving 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.  

These canals are hard to find and they are still hard for ME to find sometimes even after doing this for 10 years.  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?


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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