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Access cavity
Nawaf Hazaymeh
Aya Shahrouri
Sun. 17-2-2013
2
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In the name ofGOD
access cavity preparation
Access cavity means entrance, so we won't be able to reach root canals , or
root canal system without accessing the crown , it's the only way to reach or
to enter the root canal system by mean of access cavity through the crown.
As u can see from the diagrams shown in slide #2, it's a diagram for a molar
tooth and in order to reach the root canal system we need to open through
the occlusal surface of this molar. Each tooth has a different design of access
cavity preparation according to the morphology of the pulp chamber, so from
you're dental anatomy knowledge not all teeth has the same access cavity, so
the central incisors different than canines as well as different from the molars.
Why do we need to make an access cavity for root canal treatment?
first of all we need to Remove roof of pulp chamber in order to get access to
pulp chamber or to the root canal system, so before u start drilling, you need
to carefully assess the tooth itself by means of radiographs and as well as
examination, so you need to look at the pre-operative radiographs to assess
the suitability of this tooth to be treated or the suitability of this tooth for RCT.What do we look for in the radiographs??
1. First of all we need to make sure that root canal system is patent, whatdo I mean with patent?? not calcified or closed
2. We need to look at the morphology of the pulp or the root ** couldn'thear, so you need to know wither this root is straight or sclerosed or
calcifiedor partially with a pulp stone, so to know your way and to
predict the success of your treatment wither it's going to be really
successful treatment or it's going to be a failure from the beginning and
you are wasting your time3. And you need to look if the tooth is restored , is the restoration is
successful , is there a carious lesion beyond it
4. U also need to look the shape of the pulp chamber and the its locationbeside if its obliterated or smaller in size due to the age factors , and to
the pulp horn how far it's extending in order to determine where your
access cavity will be.
And we should know if this tooth will be easily isolated or we'll have
challenges in isolating it, also as we know we always should isolate the
tooth before entering the root canal system in order not to keep
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contaminating these canals, we need to have a septic condition or sterile
canals, otherwise what's the point behind treating these canal systems .
So from the principles of root canal treatment, why do we need to treat
the canal system what's the object behind the treatment?? First of all we
need to eradicate all microorganisms from canal system for being a sourceof infection to the peri-radicular areas, so if we don't isolate the tooth it
may affect the percentage of successful treatment of this tooth.
How do we isolate a tooth for root canal treatment??
Rubber dam is the most suitable way and if there is no enough coronal
tooth structure we won't be able to apply the rubber dam.
When you want to start drilling your tooth for access cavity preparation, if
there is any carious lesion you need to remove it, and always remember
that we need to avoid contaminating the root canal system by isolation,
removing any necrotic tissues and eradicating any focal infection.
If you felt that there's no enough tooth structure for applying the rubber
dam, then you may consider applying a durable filling like GIC, amalgam.
What are criteria for cavity access preparations?
first of all we need to remove the whole roof ( d-roof the pulp chamber) in
order to have a straight line access for the canals , we need to insert or use
our root canals instruments in a way of easily inserting it into the canal
without forcing them into the root canal system , if we fore them it willbreak if you break inside the canal it will be a nightmare for you as a
dentist and for patient as well as the endodontist you will refer this case
to, it can be removed if the patient is lucky, if you're lucky as well , but it
will take time
NOTE :
when you do the d-roofing you should achieve this step without touching
the floor of the pulp chamber, touching I mean with the bur, IF you touch
the pulp chamber with bur whenever you place the file it will engage, andif you think this is the orifice you'll penetrate or perforate the pulp
chamber, the floor will guide you or will guide your finger according to
your knowledge to the location of the canals orifice.
After d-roofing and making the access cavity neat and nice you'll be able to
see the orifice as in slide #5, when we want to do an access avity we need
to involve the whole pulp chamber walls in the cavity if you leave little bit
of pulp chamber roof and it will act as a shelf, you won't be able to remove
these necrotic tissue from underneath , as the diagram in the middle of
slide #6 ( that angle circled in red) , in this case we need to involve the
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wall above and below that angle in order to have a straight line access to
those roots as well as removing all necrotic tissues in that area.
Just to emphasize again, the access cavity is a very crucial step in
successful RCT , if you couldn't make it nice and neat, you'll face difficultiesin the following steps.
for example in this case (in the diagram below) we have two root canals
buccal and palatal canals, access cavity should involve both orifices and, so
in this case if you want to insert your file to this direction ( green arrow) , it
will reach this point and If you want to push it again you'll end up with a
perforation or penetration or at least you'll create a LEDGE : it's a
procedure error you may create by forcing the file into the canal system
where it's not in a straight line access with the root canal, what do we
need to do ?? we need to remove that angle in order to insert our file
correctly. So it would be much easier to reach the apical area.
So what do we need to have before starting our cavity preparation??
1. Pre-operative radiograph2. A knowledge of the pulpal anatomy
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3. Magnification aims in order to help you see clearly and locate orificesand canals, because we work in a tiny areas and we need to have a sort
of magnification that helps us to know where to insert our instruments.
NOTE: loupes are not less than 500-600 USD
Different types of magnification loupes
Stages of cavity preparation :
first we need to find the pulp chamber and we need to locate canals and
we ensure adequate access to the canal orifices, as I said in the beginning
each tooth has its anatomy a different shape and size of pulp chamber and
in order to that u make access to the cavity, the only way is to go through
the occlusal surface if you want obdurate the whole canal system.
(central incisor: if you look from the labial view , you need to involve these horns
therefore the shape of your access cavity for a central incisor will be triangular
shape, base incisaly and the tip above the cingulum from the palatal side, of
course you're not gonna access cavity from the labial side for a central incisor,
would you accept somebody to make your root canal system from the labial side
?!! if you accept it will be very difficult to achieve a straight line access!)
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(Thats for a canine, it's different, it will be in the centre. from the lingual side it
will be oval in shape and in the centre and it doesn't need to be extended to both
mesially and occlusaly slopes because there is no pulp horns or pulp tissue under
that area)
Just a quick revision for the objectives :
*by making the cavity access we'll have a Straight line access and that will
Improve instrument control and handling and that will :
*Minimize curvature and deflection of the instruments and at the end we'll
have a safe journey to the apex. and if you control your instruments you'll :
*Decreased procedural errors like:
-Ledge formation
-Apical perforation
-Stripping perforation* also we need to Conserve tooth structure, we don't need to involve un-
necessarily structure in deep access preparation for the sake of getting
good access to the root canals or orifices. The access cavity itself will not
decrease the strength of the cusps for a great amount, now it will affect the
tooth itself I can't deny it- but making the access cavity as small as could
be, keeping in mind involving the whole pulp chamber.
HOW to do it??
A. as I said you make access from the occlusal surface, you do a class 1
cavity procedure using round bur just to make outline, then you can
penetrate the pulp chamber by a straight fissure bur.
there is no standard burs for making cavities, we can't say this bur is
better than the other in making that cavity.
from the Dr experience : use round bur first to outline the shape of the
acces cavity then use a straight fissure bur, this is a good procedure.
B.once you penetrate pulp chamber I advise you to penetrate always the
largest canal. For example in the UPPER MOLAR, the largest canal is the
palatal.
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C. so you direct the tip of your hand-piece toward the palatal canal, you'll
feel like a drop, when there is empty space under the bur you'll feel like
your hand-piece will fall or drop. control it not to touch the pulp floor as I
said earlier, and follow the outline you drilled in the first stage.
once you penetrate you need to negotiate(not sure, but thats what I
heard) the canal orifices using endodontic probe to see if the orifices are
open, then you need to insert the small size file, and as I said I need this file
to go straightly without binding without curvature and without forcing it, if
it bends in one area it will either break your instrument or you'll have
stripping.
now here :
( if u didn't remove this black area either you'll straighten this part of the
root canal system, or you'll penetrate and perforate the root to the side)
Q: what's the difference BTW the ledge and the stripping??
A: ledge when you don't have a straight line access, so it will creates an
angle in the dentin inside the canal and whenever you inside the file again
it will engage, so you won't be able to bring it back to the canal and if youforce it will perforate the canal, and the correction of the ledge is really
time consuming.
Stripping when you keep inserting and bringing out the file in this
area you'll end up with straighten it and you perforate to the furcation area
or to the buccal or lingual area in a straight line rather than it's just on the
tip of the file.
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Zipping: the file reaches the tip of the root and if you force it the tip will rotate
in a large area not, so it will larges the part above the root apex and if you
continue it will make an apical perforation.
**Lecture on next Sunday will be in NG76
**In the Lab of this week you should bring the jaws in order to learn how toapply the rubber dam
Done by: Aya Sharouri
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