When I went through my undergraduate dental training, I was taught that MB2 canals in upper molars are there 60-70% of the time.  Newer tools and techniques show us that MB2’s are always there whether or not we can get to it.  As a matter of fact I tell our endodontic residents at UBC that “if you haven’t found it, you have missed it“.

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Here are some pointers on how and where to find the canal that can potentially result in endodontic failure if left untreated, specially if the tooth is necrotic to begin with:

1. MB2 is always there!
2. It is always located palatal to MB1.
3. It is always mesial to the line running between MB1 and P canals. This is the only safe area to trough.
4. A good magnification and illumination is necessary.
5. The access should be big enough to allow for adequate visualization of the pulp floor colour and map.
6. Only instruments/burs (such as Munce Discovery Burs) that produce smooth troughing surface should be used. This is a more conservative and much cheaper option than using ultrasonic tips.
7. There is absolutely no need for using explorer to poke and create misleading holes on the pulp floor.
8. If there is no indication of the canal initially just start by troughing from MB1 mesio-palatally.
9. Use copious irrigation to remove all debris created during troughing.
10. The troughing should continue until a small size file can easily drop into this canal. This point of entry could sometime be 2-4 mm below the pulp chamber floor.
11. Do not trough and hope you can find the canal. Always observe the colour changes on the floor and look for the clues.
12. Know your limits and when you hear the whisper in your ears asking you to stop, listen to it!