Young Bui, D.D.S.
Anatomy of Multiple Canals and Roots
Young Bui

Young Bui

WE WERE TAUGHT in dental school the very basic knowledge of root anatomy and the average number of canals in certain teeth.  This knowledge gives us the basis to perform root-canal treatment.  However, there are times when we stumble upon a unique case with an extra root or extra disto-buccal (DB) or extra palatal (P) canal.  These cases may not be too confusing if the canal is wide open and is easily engaged with a file.  Unfortunately, in some cases the extra canal is located far from the other opening and is partially calcified.  We may not try to gain access into the extra canal because we may think that it is just a dimple in the floor of the tooth or because it is not at a “normal” location for a canal. 
     The number one reason for failure of upper first and second molars is not cleaning the second mesio-buccal (MB2) canal.  You should always check to see if there is a little dimple or catch in the isthmus running from the MB canal to the P canal.  Dental textbooks say that MB2 occurs in half of all upper molars.  In my years of practice, I have encountered MB2s in 75 to 80 percent.  I tend to get nervous when I can only find one canal in the MB root.  Always assume that there are two canals until careful examination proves otherwise.  If the two orifices are close to each other, the two canals are more than likely to join at the apex.  If you have a second canal midway between the MB and P canal, then you will probably have two separate apexes. 
     Figure 1 shows an upper first molar with three individual MB canals and two palatals.  There are also two DB canals, but there was no more room to place in another file.  The three MB and P canals have separate apexes and the DB canal joins together at the apex.
     An upper first premolar usually has two canals with two separate apexes, and an upper second premolar has one or two openings ending in one apex.  There are unique cases in which you will find three canals or three individual roots in an upper premolar.  Sometimes the third canal is located right next to the buccal canal.  At other times, the third canal is located a couple of millimeters below the buccal orifice.  If an inserted file is angulated toward either the mesial or distal direction, that is a good indication of a third canal.  You will see this angulation when the two orifices are situated really close together.  If you have a large buccal orifice, but the file feels tight as it is being inserted, there is probably a third canal situated a couple of millimeters below the orifice to the side.  Widen the orifice with a slow speed #2 round bur and examine for a second buccal canal.
     Figure 2 shows an upper right second bicuspid with three individual roots and canals.  The two buccal canals are situated side-by-side close to each other.  Figure 3 shows an upper left second bicuspid with three individual roots and canals.  The second buccal canal is located a couple of millimeters below the buccal orifice.
     The frequency of occurrence of two canals in a lower first bicuspid is about 24 percent, and it is 2.5 percent for the second bicuspid, depending on the studies or textbooks you read.  The percentage for three canals or roots is given as about 1 percent or less.  I have been very fortunate, or maybe unfortunate at the same time, to have performed root canals on these two rare anatomies.  When you see on an x-ray that the tooth does not have a clear, straight canal, start searching for extra canals.
     Figure 4 shows a lower right second premolar with three individual roots.  The third canal is located about 3 mm deep into the buccal orifice.  Figure 5 shows a lower right first premolar with three individual canals. 
     When a patient has a tooth with a great-looking root canal that does not seem to heal, there is probably another canal somewhere that is causing the problem.  Try to angle the x-ray and see if you can locate another canal.
February-March 2003
Figure 1

FIGURE 1: Upper left first molar with files showing three individual mesial canals.

Figure 2

FIGURE 2: Upper right second bicuspid with three roots.

Figure 3

FIGURE 3: Upper left second bicuspid with three roots.

Figure 3

FIGURE 4: Lower right second bicuspid with three roots.

Figure 3

FIGURE 5: Lower right first bicuspid with three individual canals.

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