Richard Mounce, DDS
At one time or another, every clinician who does root canals on a regular basis has pulled out a file a little shorter than it was when it went in. Rotary nickel titanium files (RNT) fracture more than their stainless steel counterparts. A file separation can be a great teacher if the source of the misadventure can be identified and you can learn from it. A fully-focused presence during instrumentation — blended with proper RNT file use — can go a long way toward avoiding fractures. The old endodontic wisdom, "Never be a dreamer when using a reamer," applies!
Prevention of file separation is key, but once it has occurred, appropriately managing the situation can lead to the best possible outcome option for the patient or — in a worst-case scenario — loss of the tooth. Prevention of RNT fracture is primarily a function of minimizing engagement of the file, ideally 1 to 2 mm per insertion, and certainly no more than 4 to 6 mm. Crown-down instrumentation, frequent irrigation and recapitulation, an excellent hand-created glide path, and minimum, passive apical pressure during insertion are all strategies to prevent separation. Keep in mind that not all files have an equal resistance to fracture. I am a strong advocate of the K3 RNT file system by SybronEndo for its fracture resistance, excellent tactile sense, cutting efficiency, and usefulness across the widest possible range of canal anatomy.
Despite the above precautions, if a file fractures (RNT or stainless steel), the clinician should make an immediate decision about the equipment and skills necessary to remove it safely without iatrogenic risk. Removal of separated instruments is a higher-order endodontic skill and one most often performed by endodontists rather than general dentists. As a result, separation of an RNT file frequently calls for a referral to a specialist trained in its removal, even if it can be bypassed. Leaving a file fragment represents a breakdown in ideal cleansing and shaping procedures, which is why it should be removed if technically possible. However, if the clinician is in a geographic location where referral is not possible or practical (or if the patient refuses the procedure) and the fragment can be bypassed, it is acceptable to do so and obturate the canal normally. Do not place another RNT file into the same canal to attempt to shape the canal beyond the fragment. Doing so places the second rotary file at significant risk of fracture. Such a canal should be instrumented by hand with K files with frequent irrigation and care taken to avoid perforation. This is especially true in the "danger zones" of canal anatomy where dentin walls may be exceptionally thin (the distal aspect of the mesial roots of lower molars and the distal aspect of the mesial buccal root of upper molars). If referral to an endodontist is not possible and the file cannot be bypassed, irrigate the canal as thoroughly as possible above the fragment and fill to the level of the obstruction.
While the literature does not fully support a conclusion that the presence of a separated file will diminish clinical success, it most certainly does not support clinical success as the canal space alongside and beyond the fragment remains uncleaned. As an aside, do not attempt to remove the separated instrument unless you are well-versed in the techniques required for file removal and you have the required equipment. To attempt to remove the file without the right skills and equipment is to risk perforation and a diminished prognosis for the patient.
Minimizing engagement, combined with using a fracture-resistant RNT file such as the K3 and never being a dreamer when using a reamer (or RNT file), will hopefully make this a rare event. But if it should happen, referral is the best option, followed by bypassing and then obturating to the point of obstruction.
Dr. Richard Mounce is in private endodontic practice in Portland, Ore. He lectures worldwide and is a widely published author. Contact Dr. Mounce via email at lineker @aol.com. Visit his Web site at www.MounceEndo.com.