|Allan S. Deutsch, D.M.D.
Broken Endodontic Instruments:
all the complications that might occur while you are doing an endodontic
procedure, one of the very worst is instrumentation breakage—in other words,
“file separation” in the canal. Throughout my more than twenty years of
practice, breaking an instrument in the canal has always been a major no-no
for anyone doing endodontics. Recently, with the advent of rotary NiTi
instruments, the manufacturers of these instruments seem to want us to
believe that breakage is not such a problem anymore. Unfortunately, that
is not the reality of the situation. Breakage is a problem, it remains
a problem, and with the advent of NiTi instruments it is becoming an even
If it were just the instrument’s breaking in the
canal and there were no consequences, breakage would not really mean too
much. However, when we break a small-size instrument (#08 through #25),
we effectively block the canal. When the canal is blocked, we cannot remove
all the dead or infected pulp tissue. Necrotic tissue in the canal leads
to infection or chronic inflammation and endodontic failure. If we break
or separate a larger-size file, the broken section is usually easier to
get around or bypass, and we can clean out the canal adequately. However,
sealing the canal well may be difficult. Poor sealing will also ultimately
lead to endodontic failure. By the way, there is really no foolproof way
to remove broken instruments. Removal must be approached on a case-by-case
basis with a great deal of patience, skill, and luck in the equation.
The Strength of Stainless Steel
STAINLESS STEEL instruments are the most resistant to breakage, and
reamers are more resistant to breakage than files. Therefore, more than
25 years ago we switched over to using stainless steel reamers as the mainstay
of our instrumentation. However, even these instruments break.
In Figure 1, we see the most common form of deformation
of the stainless reamer, “the shiny spot.”
To keep breakage at a minimum,
examine every file before use, don't overuse them, and don't overstress
1: The shiny spot on the reamer is caused by the unraveling of the reamer’s
|| Here the flutes of the reamer (which form the cutting
edge) are starting to unravel. The flutes usually unravel if the tip binds
and we continue to rotate the reamer in a counterclockwise direction. If
they are left to unravel more, they will eventually break.
In Figure 2, just the opposite is happening. The
flutes are knotting up. Once again the tip usually binds or wedges in the
canal, and if we keep rotating the file in a clockwise direction the flutes
will eventually break.
2: Near the tip of the reamer we can see the flutes of the reamer knotting
up like a twisted rubber band.
|| Only 1mm to 3mm of the instrument should be binding
or doing work at the apical end. If more than that is binding, the instrument
can easily lock into the canal and deformation can occur. Therefore,
it is imperative to use the Peeso to prepare the coronal end of the canal,
as described in the S.E.T. technique.
The Peeso enlarges the canal so that the coronal
end of the file or reamer does not engage the dentinal walls and hence
the instrument only cuts at the apical 2?3 mm. This reduces the chance
of breakage dramatically.
Cutting in a wet canal also reduces the incidence
of file or reamer breakage. Therefore, always keep the access opening wet
with irrigating solution while you are debriding the canal.
When stainless steel instruments do bind,
luckily, we can see the deformation and act in time to throw out the instrument
before it breaks in the tooth. Therefore, I strongly suggest that
after each withdrawal of the instrument from the tooth the dentist should
examine the file or reamer closely. Look for a shiny spot or a knot.
If you see either of these, discard the instrument before it breaks in
the patient’s root.
Endodontic files and reamers should be considered
disposable instruments. One to three uses and then out. Plan on spending
approximately a total of $20 to $30 for all (SS and NiTi) instruments per
endodontically treated tooth.
The Weaknesses of NiTi
UNFORTUNATELY, the instruments least resistant to breakage are the
NiTi files, especially the rotary files. It has been reported in
the literature that NiTi begins to microfracture as soon as it is used
in the root. No matter how light your touch, the NiTi microfractures.
It is just a matter of time before the instrument fractures all the way.
In the rotary handpiece, the combination of compressive
and tensile stress causes the file to break even sooner. The faster you
rotate the file and the more you bend the rotary instrument, the quicker
it fractures. Unfortunately, NiTi instruments tend to fracture with no
visible warning. The instrument may look perfectly normal, yet fracture
in the tooth.
In Figure 3, we are actually lucky enough to see
a deformed NiTi file of “Greater Taper” before it has fractured in the
root. This is a very rare event. Certainly, if we place this instrument
back in the root it would fracture.
3: Notice the slight deformation in the flutes near the apical end of the
NiTi Greater Taper file. Next stop: breakage!
|| We can do two things to help
reduce the risk of NiTi fracture:
If you are diligent and examine every file before use,
don’t overuse them, and don’t overstress them, then you will keep your
breakage to a minimum. If you use rotary NiTi files be very careful, because
these are the easiest of all the instruments to break. Good Luck!
Examine the file for deformations every time before placing it into the
Bend the file to at least an 80-degree angle, every time before placing
it into the root, to see if it will fracture (see Figure 4).
FIGURE 4: Bending the NiTi file
before placing it into the root.
Every time you remove a file or reamer
from the canal, clean it off and examine it. If there are any shiny spots
or knots, throw the instrument out. Consider endodontic instruments disposable!
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