Welcome to the University of Michigan Dentistry podcast series promoting oral health care
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The objective of this sequence is that the student will be able to locate all the canals
in any tooth he is assigned in the endodontic clinic. It seems obvious that if you donít
locate the canals, you wonít be able to clean them and fill them and the tooth that youíre
treating is guaranteed to be a failure. The instruments that are used in this procedure
are simply a sterile, clean mouth mirror and a sterile endodontic explorer. But there are
also four requirements that you need to have completed or you wonít be successful in locating
all the canals. When students have trouble locating the canals itís usually one of these
four requirements that they've skimped on.
The first is that they should have a well designed and well-prepared access preparation
especially the fact that the floor of the pulp chamber should remain intact to guide
you to the orifices of the canals.
Secondly, the pulp chamber should be meticulously cleaned of all debris.
Thirdly, you should have knowledge of the normal pulpal anatomy and where the orifices
of the canals are expected to be located.
And four, you should look for the maximum number of canals in each tooth. If youíre
having problems locating canals make sure that youíve fulfilled all these four requirements
and then move carefully. If you canít find it then, youíre probably best to call over
an instructor and check out your findings with him. Now we want to go through and show
you where and how to look for the canals in various different teeth. Maxillary anterior
teeth usually pose no problems to students since thereís generally one canal coming
straight off of the pulp chamber so once you have access to the pulp chamber youíre into
the canal. Mandibular anterior and bicuspid teeth are similar in that they usually have
one canal leading directly off of the pulp chamber. However, in both mandibular and bicuspidómandibular
anterior and bicuspid teeth have a tendency to have two canals and you have to check each
tooth to make sure that it does have only one canal. You do this by coming in at different
angles and looking for a second canal. Come in heading towards the labial and have it
gear right down into the pulp canal coming from the lingual and go right on down. Feel
for two canals and only accept that you have one when youíre sure that you canít feel
a second.
As you can see in the cross-section diagram, you can come in through the access preparation
from the lingual heading towards the buccal, go all the way down and the wall will guide
you into a canal. If you have a second canal when you lift the file up or the explorer
and go in the other direction youíll be able to feel a little click and the file will be
going in a different direction as you slide over into the second canal. So always check
mandibular anterior and bicuspid teeth for two canals.
The maxillary biscuspids once again are usually no problem to students. The first bicuspid
usually has two canals, the second bicuspid maxillary usually has one canal but either
one could be reversed. You have to check both teeth for two canals. You do that by once
again coming in from the buccal and looking for a canal going off to the lingual, then
coming up changing the direction of your explorer, coming down and feeling for a canal on the
buccal.
A cross-sectional diagram of a maxillary bicuspid shows that if you come in from the buccal,
youíll be able to goóhave direct access right into the lingual canal. Pulling up slightly
and changing the direction of the file, youíll be able to get into the buccal canal coming
in from the lingual. You check maxillary first and second bicuspids this way to make sure
that they have one or two canals.
The maxillary molars present a little bit more problem for students. You have toóyouíre
farther back in the mouth and you have to get oriented to find three sometimes four
canals. This is an occlusal view of a maxillary molar with an endodontic access preparation
that has been prepared. As you can see, there are three and then sometimes a fourth canal.
The first canal is the mesial-buccal canal, it sits almost directly underneath the mesial-buccal
cusp, very much to the buccal and somewhat to the mesial.
The second canal is the mesialÖ the distal ñbuccal canal. Students often have problems
finding that because they look for it over here underneath the distal-buccal cusp. In
actuality, it is very close to the mesial-buccal canal and it's always lingual to the mesial-buccal
canal coming off in this direction. There is a big lingual canal uh, ómesial-lingual
canal that sits underneath the big mesial-lingual cusp. Itís almost directly lingual from the
distal-buccal canal. There is sometimes a fourth canal on this tooth. Itís considered
kind of a second mesial-buccal canal that sits one or two millimeters lingual to the
mesial-buccal canal on a line drawn from the mesial-buccal to the lingual canal so you
always want to check maxillary molars especially maxillary first molars for this fourth canal.
Hereís a maxillary molar that has been sectioned at the level of the floor of the pulp chamber.
As you can see, if you leave the floor of the pulp chamber intact during your access
preparation, it will guide you right into the canals. Comparing this section with the
graphic that youíve just seen, you can see that the mesial-buccal cuspó uh, canal sits
right up here towards the buccal right underneath the mesial-buccal cusp. The distal-buccal
canal is not so far to the distal and itís not underneath the distal-buccal cusp. But
sits fairly close the mesial-buccal canal and always lingual to it.
The big lingual canal is right underneath the mesial-lingual cusp and pretty far towards
the lingual and in this tooth we have a fourth canal, a second mesial-buccal canal. Right
here. You always want to check and make sure that you donít have one of these or if you
do, you want to find it. So you have the four canalsÖ as you can see in the graphic.
Locating the orifices of the canals is only half the battle. You have to get the files
into the canals. To do this, your file has to have the proper direction and angulation.
To get into the mesial-buccal canal, you come from the distal-lingual, down into the canal,
letting the wall of your preparation and your untouched pulp chamber floor guide you right
into the orifice and into the canal. To get into the distal-buccal, you come from theÖ
the mesial, I mean mesial-lingual and you get right into the distal-buccal canal. And
to get into the big lingual canal, you come from the buccal and youíll slide right into
the lingual canal.
A cross-section graphic shows you whatís going on when we do this. You come in from
the distal-lingual and youíll go right into the mesial-buccal canal. You come in from
the mesial-lingual and youíll get into the distal-buccal canal. And if you come in from
the buccal, youíll go right down into the lingual canal.
The mandibular molar poses similar problems to those in the maxillary molar. Itís far
back in the mouth and you have to get oriented to find three sometimes four canals. Looking
at this graphic of a mandibular molar with endodontic access preparation, you can see
that you have a mesial-buccal canal, located toward the buccal right underneath the mesial-buccal
cusp. The distal, I mean the mesial-lingual canal is not that far to the lingual. Most
people look for it way out underneath the mesial-lingual cusp but itís actually almost
in the center of the tooth. Then you have almost directly distal to the mesial-lingual
is the big distal canal. Now that canal sometimes has two canals instead of one. So you have
to check that canal, probing it in different directions to look for two small canals on
the distal instead of one big canal.
Here is a mandibular molar that has been sectioned at the floor of the pulp chamber. You can
see that the floor of the pulp chamber guides you right into the canals if it's left untouched
during your access preparation. Comparing it with the graphic that we saw before, you
can see that you have the mesial-buccal canal very far up to the mesial. The mesial-lingual
canal not quite as far to the lingual as you might expect, but almost directly mesial from
a big distal canal. Now in this case the distal canal actually has two separate canals which
we can find by probing in one direction and taking the probe out and coming out and probing
in another direction. Make sure in mandibular molars that you check the distal canal to
make sure that itís a single canal instead of two smaller canals.
When you find the orifice to the canal, then you have to have the proper angulation to
get your file into the canal. To get into the mesial-buccal canal, you come from the
distal-lingual, and it slides right on in. To get into the distal, I mean the mesial-lingual,
you come from the distal-buccal and youíll get right on into your canal. And to get into
the distal canal or canals, you come in from the mesial.
And if youíre checking for two canals which you should, you come from the mesial-buccal
and then the mesial-lingual. Make sure that you only have one canal or if you have two
canals that youíll find them.
This graphic will show you whatís going on inside the tooth. To get into that mesial-buccal
canal, you get your file over to the distal-lingual and itíll go right on down into the canal.
You can see that it would be hard to get in coming straight, straight down youíd hit
the floor of the pulp chamber. Coming into the distal ñ I mean the mesial-lingual canal
you donít have to come all the way from the distal-buccal because the canal is almost
in the mesial of the tooth. You can come pretty much straight on down and you'll get right
on into that mesial-lingual canal. To get into the distal canal, you come in from the
mesial, and youíll slide right on down into that big canal. And youíll want to make sure
you check for two canals in that distal.
Now once again if you have any problems finding the canals that youíre looking for, check
your four requirements making sure each of them has been fulfilled, especially the last
one. Always check for extra canals to make sure that youíre not missing any. Once youíre
sure that youíve done all that you can do, youíll want to check with an instructor to
verify your results.
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