Young Bui
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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
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FIGURE 1: Upper left first
molar with files showing three individual mesial canals.
FIGURE 2: Upper right second
bicuspid with three roots.
FIGURE 3: Upper left second
bicuspid with three roots.
FIGURE 4: Lower right second
bicuspid with three roots.
FIGURE 5: Lower right first
bicuspid with three individual canals.
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