Going from hand to rotary instruments

I've given many endodontic courses around the world, and I have had the opportunity to observe how dentists learn about endodontics, as well as their attitudes toward change.

Richard Mounce, DDS

I've given many endodontic courses around the world, and I have had the opportunity to observe how dentists learn about endodontics, as well as their attitudes toward change. Some embrace change rapidly and enthusiastically, while others are more reluctant. The transition from hand to rotary instruments is different for everyone. What's the best way to adapt and which system should we use are frequent questions.

I've used virtually every endodontic system on the market in North America, and I am a strong advocate of the K3 rotary system for many reasons. One of these reasons is the Shaper series of files that is part of the system. These tools have become the component of my instrument regimen that I can't work without. These files can shape the coronal two-thirds of any noncalcified molar (all canals) within two-to-three minutes predictability and with strong fracture resistance. To date, I have not fractured one clinically.

The K3 Shapers come in three tapers: .12, .10, and .08 sizes. They are just 25 at the tip and come in 17, 21, and 25 mm lengths. They have the same cross-sectional design as regular K3 files, although they do have several minor additional modifications that allow them to remove gross debris more effectively. In somewhat larger canals, such as the palatal canal of an upper molar and bicuspids, I will use the .12 shaper, followed by the .10 and .08. In small canals, the .08 is used first, followed by the .10 and .12 successively. The shapers should be advanced no more than 1 to 2 mm at a time apically and withdrawn and reinserted, and then repeat the procedure.

The manufacturer advocates the files be run at 350 RPM, but I've run them at far higher speeds (up to 900 RPM) without incident. Clinically, I use only the 17 mm shapers, because the average tooth is approximately 21 mm. If the 17 mm K3 Shaper is advanced to its full length, it is within (on average) 3 to 5 mm of the true working length. One important principle to remember when working with shapers is that canals with significant midroot curvature well short of the true working length should not have K3 Shapers advanced (especially at high speeds) beyond the level of the curvature. Advance them only to the point of the greatest curvature. Other than this caution, the less curved the canal, the greater the RPM you can use.

With such potent cutting ability and the rapidity of shaping, irrigation should be copious and performed after every file. The shapers will generate a significant amount of shavings, which can block the canal with dentin mud. Also, it is worthwhile to use K files to maintain the patency of the canal beyond the most apical extent of shaper use, which assures the operator that the canal is always negotiable.

For those not using rotary instrumentation, simply having these three files powered with an electric motor would take you a long way toward more effective instrumentation without the risk of perforation that's possible with Peeso and Gates drills used below orifice level. In my opinion, there is little indication for these drills when compared to the safe and effective coronal shaping possible with the K3 Shapers. Creating excellent shapes also greatly facilitates obturation through warm gutta percha techniques, such as the System B Continuous Wave.

If the K3 Shapers were the only rotary files used, this efficiency alone could save the operator significant time and create profitability, even if the apical third were subsequently instrumented by hand. In any case, using the K3 Shapers as described also will greatly enhance the use of .06 K3 canal-shaping files, with less coronal resistance should the clinician choose to go beyond hand-filing of the apical third and then complete the preparation with rotary files.

I welcome your feedback on what we have covered in this column.

Future editions of The Endo File will examine each of these individual subjects in more detail.

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.

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