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Gaining access to root canals, wherein the root canal
instruments can be slipped easily into the canals to reach the apical portion,
is the most important starting point of the root canal treatment. Before you
lift that hand piece to start access cavity preparation, stop and think about
the following three points.
1. Have you refreshed the knowledge of the morphology and
anatomy of the tooth you are going to treat?
2. Have you taken a good look at the tooth in the oral
cavity? Its shape, size, tilt and morphology need careful consideration.
3. Have you spent sufficient time studying the
radiograph?
Though radiograph is a two dimensional picture of a three
dimensional area, it is the only guidance for us to have a knowledge of the
internal anatomy of the tooth. You have to combine your knowledge, morphology of
the tooth as seen in the oral cavity and the radiographic picture in your mind
and create a three dimensional mental picture of the internal anatomy of the
tooth. This is a very important step because it will help to avoid many mishaps
like inability to locate root canals and perforations.
Some cases of attempted root canal treatment that I have
seen, esp., of maxillary incisors where the previous operators couldn’t locate
the canals in old patients where narrowing of root canals has occurred, were
clear-cut proof that they had not given attention to what is described in the
previous paragraph.
Next step, equally important, is to properly orient the bur
before starting to cut the tooth. See the relationship of the tooth crown and
the bur. If you are going to use indirect vision as in the maxillary teeth, take
a few seconds to see the tooth and the bur by direct vision also. After
confirming that the bur is positioned in the correct direction, you can start
cutting by indirect vision. It is necessary to remove all caries before gaining
entry into the pulp chamber.
Access
cavities for maxillary incisors
Gain access cavities only through lingual surfaces. Since the
pulp chamber is triangular in shape, the access cavity is prepared in a
triangular form with rounded corners.
See Fig 1.
If the palatal surface of the incisor is divided into three vertically and
horizontally, the initial point of entry is in the central area, just incisal to
the cingulam. Hold a fissure bur perpendicular to the palatal surface and make a
small depression. Gradually change the direction of the bur, holding it parallel
to the long axis if the tooth. When the bur ‘drops’ into the pulp chamber,
switch to a No. 4 or 6 round bur for de-roofing. One common mistake is leaving
part of the roof in the labial aspect. This will lead to harboring of pulp
remnants and bacteria in the niche, preventing thorough cleaning.
Fig 2.
When you have prepared the access cavity correctly and look
at the access cavity through a mouth mirror, you will be able to see almost half
of the root canal length.
Maxillary
Canines
The access cavity should have an ovoid outline.
see Fig 3.
Maxillary
Premolars
Though you may come across first premolars with single root canal, usually
they have two canals (Fig 4), and
rarely three canals.
The radiograph of a premolar with three canals looks fuzzy.
You can see adjacent teeth OK, but this one looks different. As you open into
the pulp chamber, the palatal canal is easy, but the buccal is very tight, and
in what looks like a slot running bucco-lingually. You will get the mesiobuccal
canal labially, distobuccal in the middle and palatal is where you first found
it.
In contrast, second premolars (Fig 5) are mostly single
rooted, though some of them may have two root canals. When there is a single
root canal, it is ribbon shaped i.e., wider bucco-lingually and narrower
mesiodistally.
Start the access cavity preparation in the middle of the
central groove and extend buccally and palatally, giving it an elongated oval
shape.
Mandibular
incisors
The access cavity may have a triangular shape with rounded
corners or ovoid, depending on the shape and size of the teeth and age of the
patient. Fig 6 A and B
Occurrence of two canals is quite common in mandibular
incisors. They are difficult to access properly. The second canal usually
appears to hide under the cingulam. When you look into the access opening, you
should be able to see two canals. If you missed one, it’s usually the lingual.
That’s because your access opening is too small from the lingual and doesn’t
afford a straight line opening to the lingual canal. So, extend the access
cavity into the cingulam and search for the second canal under the cingulam.
If you look into the access opening and see one small oval
orifice, slightly wider from buccal to lingual, you probably have one canal.
Same is the case when you see a well defined, large open canal in the
radiograph.
Your radiographic clues for two canals are:
1. The pulp chamber is visible with canals disappearing
apical to the chamber. They seem to disappear at the bifurcation. They are
smaller and are superimposed on dense tooth structure.
2. The bilateral tooth shows evidence of two canals. Due
to the angle of the radiograph, you may have a better view of this tooth.
3. Very close examination of the radiograph reveals two
periodontal ligament spaces on the mesial or distal of the root. This
certainly represents either a deep concavity or a second canal. Treat it as
though it has two canals.
Mandibular
Canines
Make the access cavity ovoid in shape, but widen it labiolingually if there
are two canals. Fig 7 A and B
Mandibular
Premolars
They are usually single canalled, but may also have two or three canals. The
access cavity for first and second premolars should be ovoid in shape. The
incidence of two canals is less in second premolars.
Fig 8 and 9.
When there are two canals, extend the access cavirty sufficiently in the
buccolingual direction and when there are three canals, widen it in the mesio
distal direction. In this case there will be 2 buccal canals and one lingual
canal.
For learning more on endodontics CLICK HERE
Ref:
1. Franklin S Weine: Endodontic Therapy 5th ed. Mosby
Yearbook Inc. USA 1996
2. Jacob Daniel: Advanced Endodontics for clinicians. J& J Publishers
Bangalore 1998
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