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10 Tips to Prevent Separation of Rotary Files Drs. Kenneth Koch and Dennis Brave

Start Discussion More by Dr. Kenneth Koch (15)More by Dr. Dennis Brave (15)

The acceptance of nickel-titanium rotary files has been without question, one of the greatest technological advances in dentistry in the last 20 years. Unfortunately separation can occur with rotary files and it is up to us to minimize and prevent it. Here are tips to do just that.

by Drs. Kenneth Koch and Dennis Brave

1. Producing Proper Straight-line Access
While diagnosis is certainly the most difficult aspect of endodontics, access is the key to successful clinical results. With the technology currently available, NiTi rotary instrumentation can predictably produce properly shaped canals (that are neither transported nor ledged), once proper straight-line access is established. Good straight line access allows an instrument to work unencumbered and avoids the need to curve multiple times, thereby reducing separation.

2. Dealing with Difficult Anatomy
Difficult canal anatomy can often create excessive torque or a dramatic increase in cyclic fatigue. This is common where two canals merge into one common canal. Take radiographs and study them before beginning a procedure. Trace the ligaments around the root system to give you a good indication of the tooth's anatomy. Also be alert for short radius curves, which stress a rotary file far more than large banana-shaped canals in maxillary molars. You've probably heard (or maybe even asked), "Why do we always take the X-ray after we break the instrument?" Take it before and keep yourself out of trouble.

3. Understanding Torque and Cyclic Fatigue
The most common stress factors that result in file separation are excessive torque and cyclic fatigue. Torque is the result of a twisting motion, similar to holding a pencil at both ends and twisting in opposite directions. This can be seen as the rotary file unwinds before it separates.¹ Cyclic fatigue is insidious and cannot be seen. It can be compared to bending a clothes hanger back and forth until it breaks. You cannot predict cyclic fatigue so it is best to discard the instrument after a troublesome canal or tooth.²

4. Design Characteristics of Rotary File
Rotary files are generally either landed or non-landed instruments. Each has their own benefits and limitations when it comes to separation. Landed rotary files work by abrading the inside of the canal walls but this action results in increased torque stress. Non-landed files, on the other hand, are very efficient in cutting and shaping but are somewhat more susceptible to cyclic fatigue. Furthermore, the design of a rotary file will influence which taper is ideal for that instrument.

A study in Japan, conducted at the Tokyo Medical and Dental University by Dr. C. Kobayashi and Dr. H. Suda suggests an electropolished, non-landed file like the EndoSequence would prepare four to five times as many canals before separation, as compared to landed files.

5. Taper
The design features of a rotary file will determine which taper is ideal. If you are using landed instruments the .06 taper files are less prone to separation because they are more resistant to torque forces. However if you are using a non-landed instrument a .04 taper file will work better since it will generate less cyclic fatigue than an .06 taper.

6. Usage Parameters
Always keep the file moving
When evaluating initial prototypes, developers test how to break files. One of the easier ways to break a file is to take it around a curve and hold it in the same place, with no vertical movement. This is especially true for large-size files. If you keep the file moving, the stress is distributed throughout the instrument, preventing separation.

Lubricate files
Never run a rotary file dry. Without lubrication, a file requires six to seven times more torque. Fortunately when doing a root canal, the sodium hypochlorite will act as a lubricant, but at the beginning you should also use a standard dental lubricant.

Never force an instrument
Rotary instrumentation is light-handed dentistry. Forcing a file may stress an instrument to separate. To avoid force, use the next-smallest size file or recapitulate and repeat the sequence. You can also go to a smaller taper or hand file to create a glide path to facilitate the use of subsequent rotary files.

Try a torque control engine
Separation due to torque can be managed with regular engines; however, for the majority of dentists, torque control engines are advisable. They can help reduce the occurrence of separation from excessive torque. These act as a safety cushion but are not a substitute for proper technique.

7. "Cycling" of Instruments
Dr. Ali Nasseh, an endodontist from Boston, developed a system of using multiple hand pieces. It addresses the issue of cyclic fatigue, particularly critical since it cannot be seen. This is how he describes his procedure:

The advanced EndoSequence technique is based on the concept of sharing the task of cutting dentin among several files, while emphasizing the fact that each file only removes a small amount of dentin in a crown down fashion. This minimal cutting and the usage of several files in a predetermined sequence, along with this file's triangular cross section, imposes minimal torque on each file. The sequence of files used in this technique is referred to as a "cycle." A series of files is laid out in sequence in this cycle and the first file is followed by the second, third, and so on until the last file is used at the end of the cycle. Once the end of the cycle is reached, the file sequence is repeated from the beginning for a second cycle. Multiple cycles are used until the desired file reaches the apex. The final file is the Mater Apical File, which will be fitted with the corresponding EndoSequence or Active GP cone and obturated. The EndoSequence files in each cycle consist of sizes 40/.04 through 20/.04 in descending order or size. Therefore, each cycle consists of a total of five .04 constant taper EndoSequence files.³

For more on this method, please visit www.nasseh.net.

8. Single Use
Perhaps the easiest and best way to prevent separation is to use rotary files only once and then discard them. Since new files increase efficiency and productivity, it makes little sense to use files multiple times. Some clinicians will discard files after one molar case but will re-use them after anterior and premolar procedures. This decision depends on the curvature associated with the teeth and the cyclic fatigue generated.

If a file isn't new, when opening a sterilized package, you have little knowledge as to its previous use and wear. It's hard to argue against the benefits of single use.

9. Smart Operatory Management
Organization is vital. The treatment room and cabinets must be kept orderly. Make certain there is an order to the presentation and storage of both instruments and materials. Inventory control is paramount to sensible efficient endodontics.

Make good use of your assistant just as you would in prosthodontics. Make sure someone visually checks and wipes off each instrument at the end of the sequence. Any unwound instruments need to be immediately discarded. The instrument should also be passed through the beam of the dental light. This will help to prevent separation because previously missed unwinding will deflect light making it apparent. Effectively utilizing an assistant can make preventing separation much easier.

10. Think
Analyze a case thoroughly before performing it. Think about the difficulty, whether you should refer the patient to a specialist, and what the most practical and safe procedure would be. Addressing these concerns prior to treatment is critically important and is the key to making endodontics work. Don't hesitate to refer a difficult case. Specialists are there for a reason.

Conclusion
Above are 10 tips to reduce separation of rotary files. While it is true that you can never completely eliminate instrument separation, you can significantly reduce its frequency. Distilling it down to one sentence of advice we suggest using rotary files once and discarding them. Do the case, discard the files and work smart.

References
  1. Separation as a result of torque usually occurs in the apical 1-3mm
  2. Separation as a result of cyclic fatigue usually occurs higher in the shank, such as 5-6mm
  3. Personal communication, July 10, 2008
Author’s Bio
Dr. Dennis Brave is a diplomate of the American Board of Endodontics, and a member of the College of Diplomates. Dr. Brave received his DDS degree from the Baltimore College of Dental Surgery, University of Maryland and his certificate in Endodontics from the University of Pennsylvania. He is an Omicron Kappa Upsilon Scholastic Award Winner and a Gorgas Odontologic Honor Society Member. In endodontic practice for more than 25 years, he has lectured extensively throughout the world and holds multiple patents, including the VisiFrame. Formerly an associate clinical professor at the University of Pennsylvania, Dr. Brave currently holds a staff position at The Johns Hopkins Hospital. Along with having authored numerous articles on endodontics, Dr. Brave is a co-founder of Real World Endo.

Dr. Kenneth Koch received both his DMD and Certificate in Endodontics from the University of Pennsylvania School of Dental Medicine. He is the founder and past Director of the New Program in Postdoctoral Endodontics at the Harvard School of Dental Medicine. Prior to his Endodontic career, Dr. Koch spent 10 years in the Air Force and held, among various positions, that of Chief of Prosthodontics at Osan AFB and Chief of Prosthodontics at McGuire AFB. In addition to having maintained a private practice, limited to Endodontics, Dr. Koch has lectured extensively in both the United States and abroad. He is also the author of numerous articles on Endodontics. Dr. Koch is a co-founder of Real World Endo.
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