Most of us at one time or another have pulled a rotary nickel titanium (RNT) file out of a canal to find that the file is a little shorter than it was before insertion, prompting the sinking feeling known as the “heartache of separation.” At present, there are an ever larger number of RNT instrumentation systems available in the marketplace. Fracture of RNT files is the single greatest problem with their use despite the dramatic improvement they represent in enhanced shaping of root canal systems.
Separation can be very rapid, unpredictable, and create a great deal of stress for both the patient and doctor. Prevention is the key, as retrieval of separated RNT files can be very difficult and sometimes not possible. Removal of separated RNT instruments is a microsurgical procedure most often accomplished by an endodontist specially trained in their removal. The purpose of this article is to aid the general practitioner in minimizing this therapeutic misadventure.
TEN STEPS TO PREVENTING INSTRUMENT SEPARATION
The following suggestions should help prevent the heartache of RNT instrument separation (Figures 1 through 7): (1) Do be gentle and deliberate in your motions with these files. Never put more force on a RNT file than you would use on a soft lead pencil.
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| Figure 1. The “Heartache of Separation.” A rotary nickel titanium file was inappropriately placed into a canal at 1,500 rpm and full torque, and fractured mid root. |
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| Figure 2. File removed microsurgically and the canal obturated. Prognosis is excellent. |
Figure 3. Fracture of this rotary nickel titanium file occurred because the operator took the file to the end of the root without establishing a proper glide path. |
(2) Do take your time in achieving excellent shapes. Never use these instruments in a hurry. RNTs will save time in some cases, but not all. The stress and costs associated with RNT file separation must be weighed against the extra few minutes that using these instruments properly entails.
(3) Do create a glide path with small K files (6’s and 8’s) up to approximately a 20-K file to true working length prior to engaging a RNT file in the apical and middle third of any canal. Do not put RNT files into canal spaces not first explored with such hand instruments.
(4) Do instrument in a crown down sequence. Crown down instrumentation means to instrument the coronal third first, middle third second, and apical third last. Do not try to take a RNT file into the apical third without instrumenting the upper two thirds first and making certain that the glide path is established to the true working length. Taking the RNT file into the apical third without properly instrumenting the upper two thirds first puts the RNT file at a significant fracture risk. Using a tapered RNT instrument first, such as the 0.06 K3 files (SybronEndo) from the larger tip sizes to the smaller, incorporates crown down instrumentation as each successively smaller file progresses further down the canal passively. (Figure 8)
(5) Do wipe the flutes of the file after every use. Do not allow debris to build up on the flutes of the files; doing so creates a greater load for the instrument to carry, which increases the risk of fracture.
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| Figure 4. Canal obturation after microsurgical removal of the separated instrument and re-treatment of the other 2 canals. |
Figure 5. Multiple files separated in the same tooth. Removal is complicated by the horizontal component of the files’ existing position that is not evident radiographically. |
| Figure 6. File removal complete prior to obturation. |
(6) Do pull back at the first sign of resistance in the canal. Do not apically force a file that does not want to go. The motion in entering a RNT file into the canal should be smooth, deliberate, and in approximately 1- to 2- mm deeper increments relative to the last instrument. Separation can occur in a fraction of a second if the file is used forcefully.
(7) Do always use either EDTA or sodium hypochlorite in the canal when instrumenting with a RNT file. Do not instrument dry. Instrumenting dry can create a plug of apical dentin mud and increase the risk of transportation or fracture.
(8) Do check the flutes of these files after every use. Many endodontists use these files in only 1 tooth and then discard them. If the files are used more than once, in my opinion it would be ill advised to use them on more than two teeth before disposal. If a RNT is bent, stretched, or has a shiny spot, discard it immediately.
(9) Do take RNT files to the true working length, but only in canals where the RNT file will easily go to length. In delicate apical anatomy, RNT files are absolutely contra-indicated unless preceded by significant hand instrumentation, and then only if they slide relatively easily to length. In some canals, the apical third must be instrumented by hand. For example, some canals have curvatures both in a mesial-distal and a buccal-lingual plane, resembling a pigtail. Such canals are very much at risk for RNT separation and are best treated by hand.
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| Figure 7. Case completed; although not aesthetic, prognosis is excellent. |
Figure 8. Using a tapered rotary nickel titanium instrument first, such as the 0.06 K3 files (SybronEndo), from the larger tips sizes to the smaller incorporates crown down instrumentation as each successively smaller file progresses farther down the canal passively. |
(10) Do use an electric motor to power the files. Air-driven gear reduction handpieces tend to have variable torque and rotational speeds that predispose the RNT to fracture in certain canals. Following the torque settings, manufacturer’s instructions, and automatic presets on some electric models are key for effective use of the files. Do not rely on a warning signal sound or auto reverse to know when to discontinue use of a file. Some files are designed to be used at high rpms and full torque only in the coronal third of a canal, and if used apically can fracture very quickly, especially if the operator is waiting for a warning sound, which the machine may not be programmed to deliver.
CONCLUSION
Following the simple steps above can go a long way toward eliminating the “heartache” and providing the joy of more predictable and profitable endodontics. Both we and our patients will appreciate it.
Dr. Mounce has a private endodontic practice in Portland, Ore. He lectures worldwide and has written numerous articles for journals such as Dentistry Today and the Journal of Endodontics. He will be presenting multiple 1-day courses (lecture, hands-on, and demonstration included) on cleansing, shaping, and obturation of the root canal system in Southern California in September. For more information, e-mail him at lineker@aol.com.
