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Figure 1 Referral Preop

April 2007 – A Perforated Mandibular Second Molar?

This 567 year old male patient was sent to me by a referring dentist who does much of his own endodontics. The patient originally had a crown on this mandibular right second molar. The tooth had a large area of decay under the distal aspect of the crown and the crown needed to be replaced. The dentist anticipated that the tooth would require endodontic treatment prior to re-restoration. (Fig. 1) Since the anatomy and canal configuration seemed to be fairly straightforward, he elected to treat the case himself.

The crown was removed and the caries excavated to sound dentin. The Dentist made what he thought was a normal access cavity and placed some files into the canals to try to obtain working lengths. The dentist noted that the canals bled more than normal and that he had difficulty getting the mesial aspect of the access free of bleeding. He then was alarmed to see a file, apparently right in the furca area. (Fig.2) He immediately suspected a perforation and referred the case to me for further treatment..

Figure 2  - Referral WL

The canals seemed to be clearly visible on my preoperative radiograph. The tooth appeared to be a two rooted molar and a second preoperative image did not reveal a separate lingual root. (Had a third root been present, the canal would likely have been on the lingual side and NOT on the buccal side as was described to me in the referral letter.) I was puzzled as why the file so easily penetrated the furca. Closer examination of the access preparation showed it to be fairly conservative and there was no reason to suspect that over-aggressive use of a bur had penetrated the furca area and caused a perforation. So what was the problem?

My working length files also showed that I was clearly in BETWEEN the mesial and distal roots with the MB file. What was even more puzzling was that the apex locator was giving me normal readings. There was no indication that a perforation had occurred and as I slid the file into the access the readings appeared to transition properly as the file moved toward the foramen.

With the use of some Munce burs and Carr Ultrasonic tips, the reason for this unusual situation eventually became clear. Deeper troughing of the isthmus between the canals revealed that all canals were connected in the coronal aspect. This was a C shaped mandibular second molar canal system. The "middle" file had not perforated the case. There was a canal (the MB canal) in this area. It was just that the dentin in this part of the root was so thin that the file appeared to be in "no man's land", right between the two roots. (Figs 4 &5.)

Figure 3 - My Preop Figure 4 - WL Files #1

Figure 5  - WL files #2 
Where does that file go ??!!
Figure 6 - Cone Fits
Figure 7 - Final #1 Figure 8 - Final #2

The completed case( Figs. 7 &8) shows three separate canals. You can also see a small bit of coronal extension of the Distal gutta percha fill into the mesial aspect of the "C".  This is why it looks so wide coronally. It does not exhibit the classic "curtain shape" that we see with a C shaped fused molar root canal systems, but it is  a C shape nonetheless.

Rather than provide one distinct post space (as the dentist requested) I suggest that we merely leave some retention spaces in the coronal aspects of the filled canals. This should provide more than adequate retention for the subsequent core restoration.The referral was relieved to hear that he had not perforated the case and I was also glad that I did not have to do a perf repair in the furca.

This case shows that although we rely heavily on radiographs for interpretation of the canal and root anatomy, they can often be deceptive, especially in anomalous teeth and areas of the tooth that are particularly thin. We must use multiple methods and our experience to try to anticipate the canal system anatomy.