How do we find the "second"mesio-buccal canals? I "map" out the positions where I would expect the canals. The second mesio-buccal canal usually lies on the line from mesio-buccal (one) to palatal canal, but the second mesio-buccal canal will lie slightly mesial to this imaginary line and slightly closer to palatal canal.
The pulpal floor is generally smoother and slightly darker in shade than floor of tooth. The canals usually lie in a depression in the pulpal floor except for the second mesial buccal canal. The pulpal chamber is contained and "walled" and so it is often easy to see the border and investigate the openings to the canals. We look for all complexities and changing anatomy of the canal architecture and lay out. Fine so far.
Let's take a look at the following molar teeth below:
Upper left molar teeth with very deep fillings and apical lesions above both molars.
Our patient was planning to have complex and full restorative treatment that would include moar teeth. The patient had discomfort from her teeth and root canal treatment was advised for both teeth. See below:
Root canal treatment completed for both upper molar teeth
Root treatment was completed successfully with good radiologically sound fillings. The pulp chamber was investigated carefully and all root canals were located and treated. Look closely at the x-ray. The patient had a nagging discomfort related to her teeth after 2-3 months. There was a concern that a root fracture was present and causing this discomfort and I was asked to investigate. I reopened the second molar and noted that the palatal canal opening was slightly distal to its "normal" position. The pulp chamber "border" was recognised. But I also noted that there was a slight bulging of the mesio-palatal root anatomy. I removed more of the mesial margin wall towards the palatal direction and noted a slight staining point. Probing revealed a "soft" spot and a fine file located the entrance to a second palatal canal. The canal opening was not part of the main pulpal chamber! Or so it seemed to me at this level. The canal was cleaned and obturated to apex. See below:
Second mesio-palatal canal treated to length in four root molar tooth
This upper second molar tooth had four separate and distinct roots. It seems obvious now in retrospect. Doesn't it always. This case reminds us of the complex anatomy of molar teeth and teeth in general. Always expect the unexpected and make sure to interpret the x-rays correctly. Please see other examples of complex root canals