The Importance of Mid-Mesial Canals, Tooth #31

Unusual anatomy of a mandibular second molar

Nonsurgical root canal therapy was performed on #31. During the procedure a mid-mesial canal was detected just lingual to the mesio-buccal orifice, via troughing with an ultrasonic tip and the aid of a dental operating microscope. Radiographs were taken to reveal an abrupt, midroot canal curvature and portal of exit in the furcal area. (See images 1-4)

• As in any case, detection and subsequent cleaning and shaping of all canals is vital for RCT success. As it pertains to mandibular molars, a clinician must always evaluate for the presence of a mid-mesial canal. Literature varies greatly regarding the prevalence of this anatomic feature (see attached articles for more information), but the current best evidence says it’s there roughly 20-40% of the time.
• So why does this matter? If left untreated, any tissue or necrotic debris left in the space may be sufficient to cause treatment failure. I particularly like this case because it illustrates another great point. Here, the mid-mesial canal doesn’t join one of the two other canals (as they do in the majority of cases); rather, it has a portal of exit in the furcal area. If that canal wasn’t treated, and it led to the formation of a lesion in the future, that would manifest as a furcal radiolucency on a root canal-treated molar…and we all know what that sounds like. Fracture! Dentists may assume this and prematurely extract a perfectly salvageable tooth.
• The take home message here is twofold: as a clinician, if you are performing RCT on a lower molar, be on the lookout for mid-mesial canals.  This often requires the illumination an magnification of a microscope. As a diagnostician, don’t immediately assume that a furcal lesion on a root canal-treated molar is a crack.
• http://www.jendodon.com/article/S0099-2399(14)00786-9/
  http://www.jendodon.com/article/S0099-2399(14)00900-5/pdf