Allan Deutsch
 
 
 
 
 
 
 

ANDIBULAR BICUSPIDS can be among the most difficult teeth to treat endodontically. The problem revolves around the number of canals in the tooth. Obviously, if there is only one canal, there is no problem. However, the first premolar can have two canals with two separate foramina 25 percent of the time and the second premolar can have two separate foramina 3 percent of the time (see Table 1). The question then becomes: is there any easy way to tell how many canals are in these teeth?

TABLE 1: From Textbook of Endodontology, Blackwell Publishing 2003, page 240

    Luckily for us, two-canal bicuspids have a very distinct recognizable radiographic appearance. When we look at a two-canal bicuspid in the M-D radiographic plane, we will see a very large canal that either disappears or becomes very thin about halfway down the canal (Figure 1). If we were able to rotate the tooth 90 degrees to see the B-L plane, we would see that it becomes radiographically thin or disappears where the one large canal now splits into two independent separate canals. This is the radiographic key to understanding how many roots there are. The degree of difficulty in doing endo on this type of tooth depends on how far down the root or how close to the apex the one canal splits into two. The closer the split is to the apex, the more difficult the root canal treatment becomes! The arrows in Figures 2 and 3 point to where the primary canal splits in the illustrated bicuspids. Since the split is relatively high up in the canal, these cases are not too difficult to treat endodontically.

Figure 1	Figure 2

    Recently, I treated just such a case—but with a little twist. Figure 4 shows the pre-op view of tooth #21 when the patient presented in the office. A general dentist had made access and attempted to find the canals, but to no avail. I did not know whether what the radiograph showed was the natural anatomy or had been created by the dentist when looking for canals. It certainly had the appearance of a large canal that split. Tooth #20, which had not been touched also had this appearance. Many times, if one bicuspid splits, the other may also. After about ten minutes, I found one canal a little off center towards the buccal. I instrumented this canal fully. Sometimes when you instrument the canal fully, you can more easily see where the canal is in relation to the anatomy of the root; that relationship helps in locating the next canal. Unfortunately, it did not help me in this case. I spent the next 45 minutes looking for canal #2 without success.
    Essential Dental Systems recently released EZ-Fill® Xpress epoxy root canal sealer. This sealer is extremely radio-opaque. I have often noticed at our hands-on courses that if you seal one canal without instrumenting the other, the sealer flows into the uninstrumented canal and it can readily be seen on x-ray. I thought that if I followed that procedure in this case the sealer might show me where that other canal was located. I filled the buccal canal with gutta percha and EZ-Fill. Luckily for the patient and me, the sealer cooperated and did exactly as I wanted. If you look at the x-ray on the right in Figure 5 you will see a little puff of sealer going to the left of the gutta percha filling. The puff starts at the base of the widened portion of the canal. It is the lingual canal. It was much more lingual than I had thought or was looking at. Drilling more lingual, within two minutes I was in the second canal. Figure 6 shows the final result. If I had missed that large canal, this case would have surely ended in failure.

Figure 3	Figure 4
Figure 5	Figure 6

     The take-home lesson here is: know your radiographic anatomy and keep plugging away..

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