Barry Musikant
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dentists instrument canals with .02 tapered stainless steel reamers or
files. They may open the apex anywhere from a #15 to a #40. Having instrumented
with .02 reamers or files, they then obturate the canals with .02 tapered
gutta-percha or standardized (I.S.O.) or (standardized points). Generally,
the canals and the point are coated with cement and the pre-fitted point
is placed into the canal, followed by the addition of extra points in a
combination with vertical and lateral condensation.
As you may know, although the fit film is placed accurately to
the apex, the final film often shows gutta-percha over the apex. You might
logically decide that you used too much vertical force. What you should
understand is that you are placing an almost parallel gutta-percha point
into an almost parallel preparation. An .02 taper is very close to parallel.
Is it any wonder, therefore, that a small amount of condensation then results
in overfill?
An alternative is to shape your canals with greater taper and place
points of greater taper, making it more difficult to drive the points over
the apex, even if you apply significant vertical condensation. Because
of this greater resistance, you will have fewer unpleasant discrepancies
between your trial fit and final cementation.
Buchanan designed a set of files of greater taper going from .06
mm/mm to .12 mm/mm. These tapered files correlate almost exactly to various
tapered gutta-percha points. For example, the .06 file of greater taper
correlates to a fine-medium point. The .08 file of greater taper corresponds
to a medium point.
Both Buchanan files will bind exactly at the apex. As good as these
files are for creating proper shapes, they should not be used from the
start of instrumentation because they would be subjected to considerable
stress
Since they are made out of Ni-Ti, they can break without warning
despite showing no signs of wear.
Using Ni-Ti Instruments Without
Fear of Fracture
To take advantage of these Ni-Ti instruments without fear of fracture,
shape your canals first with a step-back sequence using the .02 tapered
stainless steel reamers. The sequence consists of the following steps:
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Determine the distance to the apex. (We obtain greater accuracy from an
apex locator than x-rays. We’ve used a unit from Osada for years)
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Coat all files and reamers with RC Prep and irrigate copiously with with
5.25 percent NaOCL delivered with a 30 gauge needle used with very light
pressure.
A 30 gauge needle allows you to irrigate efficiently
near the apex as the shaping progresses. The light pressure prevents the
solution from going peripically. Remember, only a few drops are necessary
apically to thoroughly fill the canal space with fluid, and time is necessary
for the NaOCL to digest the organic debris and kill residual bacteria.
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Instrument to the apex through a #20 reamer using a rotational motion.
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Track the canal 1/3 to 1/2 its length with a #2 Peeso reamer, tapering
the canal in the process. Minimal force assures no ledging or blocking.
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Recheck your apical patency with the #20 reamer.
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Go 1 mm short of the apex with a #25 stainless steel reamer.
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Go 2 mm short of the apex with a #30 stainless steel reamer.
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Go 3 mm short of the apex with a #35 stainless steel reamer.
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Go 4 mm short of the apex with a #40 stainless steel reamer.
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Go 5 mm short of the apex with a #45 stainless steel reamer.
Checking your patency after each reamer is a good
idea. Having used the stainless steel reamers through #45 in a step-back
fashion, you now have created a canal shape with a .05 taper using .02
tapered instruments! The increasing stiffness of the thicker stainless
steel reamers have not distorted the canal shape because as the reamers
become progressively wider, they go diminishing distances. This sequencing
is an excellent safety device.
If by chance you initially over-instrument, you
will not compoud the problem by repeatedly injuring the peripical tissues
because the technique requires you to pull back. At this point in the process,
you are more than halfway to achieving an .06 or .08 tapered canal space.
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Employing a balanced-force technique, use Buchanan’s .06 file of greater
taper to the apex without applying a lot of pressure. The final shape,
going from a .05 taper to a .06 taper should take less than 30 seconds.
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Once an .06 taper is achieved, you can automatically fit a fine-medium
point, or you can choose to shape the canal with an .08 file of greater
taper, which should take you no more than an additional 90 seconds followed
by a trial fitting of a medium gutta-percha point.
A key point in using Ni-Ti instruments is to prevent
heavy hand pressure and binding. If you use light hand pressure, the binding
is minimal. You will remove less tooth structure at any one time, but will
be compensated for it by increasing the number of instrumentation cycles.
A higher number of cycles combined with reduced hand pressure prevents
the Ni-Ti instrument from reaching its elastic limit.
Distortion occurs only after reaching its elastic
limit, and Ni-Ti easily fractures when reaching this point without any
tell-tale signs. An additional advantage is that as delicate as Ni-Ti is,
it will last almost indefinitely, if the elastic limit is not violated.
The Bi-Directional Spiral
The placement of a well-coated tapered gutta-percha point into a well-coated
tapered canal drives the cement into accessory invaginations if they exist
and ensures the safe release of excess cement coronally.
The bi-directional spiral (BDS) is the most effective
way to safely place cement on all walls of the preparation. The BDS creates
lateral movement of the cement while preventing it from going over the
apex.
EZ-Fill cement is used to coat the canals and the
prefitted tapered gutta percha point. It has the following advantages:
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It is non-toxic and non-inflammatory.
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It is eugenol-free.
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Because it is an epoxy resin, it’s compatible with composite chemistry
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It bonds to dentin and gutta-percha.
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It is highly radiopaque.
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It neither shrinks or expands.
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More than 45 years of research back its use.
After coating the canal, coat the last 4-5 mm of the tapered gutta-percha
point, place it into the canal, and sear off the excess material. A single
tapered gutta-percha point is all that is required. Coronally, the thicker
cement seal stays perfectly intact. Displacing it with further point placement
will achieve nothing.
The time requirements for this sequence from start
to finish on a non-calcified single canal should be less than 20 minutes
(with practice).
The money invested in this technique is minimal
because the emphasis is on inexpensive traditional stainless steel reamers
and regular tapered gutta-percha points.
We believe that this technique is truly the best
of both worlds, resulting in superbly shaped canals, a well-fitted gutta-percha
point with a continuous epoxy resin interface that has been driven into
any invaginations that may have existed, produced in a time-efficient and
economical manner.
Nothing else comes close!
11/02/1999
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A key point in using Ni-Ti
instruments is to prevent heavy hand pressure and binding. If you use light
hand pressure, the binding is minimal. You will remove less tooth structure
at any one time, but will be compensated for it by increasing the number
of instrumentation cycles. |
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