As if dealing with MB2 canals in upper molars was not complicated enough (see my previous post on MB2 canals), here is another thing to consider when doing root canals on lower molars:
The presence of an independent Middle Mesial (MM) canal has been reported for decades in endodontic literature. Owing it to technological advancements, it appears that the incidence rate for these extra canals is on the rise: Skidmore & Bjorndol 1971 (0%), Pineda & Kuttler 1972 (0%), Vertucci 1984 (1%), Fabra-Campos 1989 (2.6%), Goel et al. 1991 (15%). I even hear incidence rate of up to 60% based on the more recent micro-CT studies. This may be pushing it though!
It is really important to realize that MM canal could exist and therefore, the area between MB and ML canals in lower molars should be explored thoroughly during accessing, locating canals and instrumenting.