Broken Endodontic Instruments

Allan S. Deutsch, D.M.D.
Broken Endodontic Instruments: Watch Out!

Allan Deutsch

f 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 larger problem.
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 them.

FIGURE 1: The shiny spot on the reamer is caused by the unraveling of the reamer’s flutes.

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.

FIGURE 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.

FIGURE 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:

Examine the file for deformations every time before placing it into the patient’s mouth.
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).

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!

November-December 2000

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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