July 2002 – Missed MB2 - The Importance of Separate Foramina

July's Case of the Month relates to the classic endodontic referral of failure to heal in the maxillary molar. Very frequently this is due to a "Clean Miss" of the 2nd canal in the Mesio-Buccal root. This canal ( commonly called MB2 or he Mesio-Lingual canal) is one of the most common reasons for failure of treatment. We will examine this case radiographically and give you hints as to how to locate the canal.

Fig. 1.	Fig. 1 shows the case as it presented in a 32 year old male patient. Treatment had been completed several years previously and the patient now presented with percussive sensitivity and tenderness to palpation over the MB root apex. When examining the film, I noted that the DB canal fill was obviously short and that there was the radiolucency at the MB apex. I also noted what appeared to some "buckling" of the gutta percha cone in the palatal canal that indicated that the obturation may not have been optimal in that root as well. The most striking feature of the film was the appearance of the mesial canal filling. It did not appear to be "centered" in the root. This indicates that a second canal is present, that in this case had not been detected. Access was made and the gutta percha was removed from the canals. Upon further examination my suspicions were confirmed, it was a clean miss of the MB2. ( Fig. 2)
Fig. 2	Working length files were placed in all canals. ( The larger files represent canals that had already been treated.) Although my working length file (#15) was long, I was more concerned with the obvious fact that the foramen in this canal did not join MB1. In other words MB2 appeared to be a totally distinct canal.
Fig. 3	All canals were cleaned shaped and then a cone fit film was taken with gutta percha cones in the MB and Palatal roots. ( Fig.3) I was unable to unblock the distal canal but I was less concerned about that because of the lack of pathology associated with the DB root. My main concern was obtaining a good seal in the MB root and improving the quality of the fill in the palatal root.
Fig. 4	Fig. 4 shows the result of the fill immediately after treatment. I also mentioned to the referral that there appeared to have been an amalgam repair of the distal crown margin and that this was not acceptable. The crown needed to be remade. As well, I had some suspicions about mesial caries in the second molar and asked the restoring dentist to examine this area once the crown was removed.
Fig. 5.	Fig. 5 shows a 6 month recall film . The patient's symptoms were gone and the temporary restoration was ready to be replaced with a permanent crown. ( No restoration of the mesial caries in the second molar yet !)

Summary
When examining the MB root of a maxillary molar, always look to see if the canal is "centered" in the root. (Best determined with a radiograph of a working length file.) If the canal appears to be "off to one side of the root" then the chances are that you have a second canal in this root.

Many of us have been fortunate in the past. The foramina of MB1 and MB2 frequently have a common exit and you may "get lucky" without filling MB2, especially if the amount of pulp tissue in MB2 is small and the case is vital. ( Note: that is NOT an excuse for NOT filling this canal! Its almost always THERE , you just have to find it ) However, when there are two distinct canals, BOTH canals must be found and treated or the case will not heal.

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