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August 2003 – "Middle Mesial " Canal in Mandibular Molar
Previous case of the month examples have shown us how the mandibular molar can vary with regards to number of roots and canals. As greater visibility is gained through the use of the SOM ( Surgical Operating Microscope) many structures that may have been previously missed can now be clearly identified. The "Middle" Mesial canal is one such canal.
The "Middle" mesial canal occurs between the MB and ML canals in the mesial root of mandibular molars. It is fairly rare and I don't believe there has been a serious study of the frequency of occurrence. Some guesses have estimated that they occur in 1% of cases. However, when this canal is missed, it can frequently be very difficult to diagnose. The Mesial canal fills look normal ( 2 canals are filled well on the radiograph) yet the patient remains symptomatic. Fortunately, this canal often joins one of the other canals ( MB or MB) in a similar manner to MB2 in upper molars and many cases that have them are asymptomatic because of the seal of the common foramen.
Fig. 1 - Preoperative film - Typical Mandibular first molar
Fig. 2 - Working length image showing 3 instruments in three separate canals
Fig. 3 - #10 file placed into the Middle Mesial Canal. The other two canals have already been shaped
and instruments removed so you can see the Middle Mesial Canal more clearly. In this case the
Middle mesial joined to the ML about 2 mm from the apex.
Fig. 3 - All 3 mesial canals ready for obturation.
Fig. 4 - Obturated canals with Orifice Bonding agent applied to prevent leakage.
Fig. 5 - The Mesial canal fills have a typical "multiple-fluted canal" appearance of the gutta percha fill.
Because the canals were so close together and had formana that were almost common, a mesial shift
shot did not reveal much canal separation.
A mandibular molar with three separate orifices in the mesial root was presented. Many variations of canal system anatomy exist in this tooth. The misconception that cases can be viewed radiographically and then judged as a "simple two rooted or three canal molar" can result in underestimation of the canal system complexity. The SOM allows for greater visibility and confirmation of such anomalies and therefore is more likely to produce cases that are cleaner and better shaped. Always look for the "extra" canal. You will be surprised at how frequently it will occur.