Mechanized Ni-Ti Rotary Endodontics

OK. I’ll admit it. I was a cynic. I really wondered what the “big deal” was all about when it came to Rotary Ni-Ti instrumentation. I had been using hand reamers with the “Standard Boston University Technique” for my first  16 years of practice (starting in 1986)  and was having very good success with them. If there was any criticism of the canal shapes it was that some of the clinicians using rotary Ni-Ti shaping techniques believed that the larger cervical canal diameters achieved with this hand instrument technique were no longer needed with the increased flexibility of Ni-Ti metallurgy.

I believed (and still do) that Schilder was really the grandfather of the concept that THE MOTION OF THE INSTRUMENT – NOT THE INSTRUMENT ITSELF – is what makes the canal shape. Unfortunately, back in the 1960s Schilder did not have the ability to use instruments of varying tapers and different metallurgy because they were not invented yet. He compensated for this lack of varying taper by varying the diameter of the reamer …His main shaping instrument. He originated the idea of the “Envelope of Motion” – created when a reamer (with its cutting area bent in a curve) was used in rotary/withdrawal fashion. (Wow ! Sounds a LOT like what we Ni-Ti rotary users do today!) If you really examine this idea closely you realize that this was his way of creating instruments of varying taper, depending on the size of the reamer and how much bend was put on it. i.e./ smaller bend = less taper= less work = thinner shape, larger bend = greater taper= more work = thicker shape. In this way he could “customize” the taper of each set of reamers (depending on how much bend (i.e./ work) he wanted each particular reamer to do. Voila ! Greater tapered instruments, depending on how you used them in rotary motion. In an era of “stepped preparations” and cookbook endo, his technique created custom tapered shapes that flowed with each canal. And with it Endodontic obturation finally got what is known as “The Look”.

Because my Master’s Thesis had dealt with the Envelope of Motion, I must admit to some reluctance in substituting Ni-Ti rotary for a technique that had served me so well for 16 years as an Endodontist. The fact was that many of my fellow clinicians were getting marvelous results with less “sweat”. They were creating more “conservative” preparations while still getting beautiful shapes and fills. There was no question that many of the failures that I was seeing over my 16 years of specialty practice were frequently associated with vertical root fractures. I knew that anything that I could do to remove less dentin during canal preparation (while still maintaining proper shape) would likely reduce the chance that these fractures would occur.

My initial foray into Ni-Ti was disappointing. I was using an NSK Endo Mate handpiece with Quantec files. It seemed like I was breaking instruments every second or third case, which was very frustrating. I was able to bypass many of the files but it was very expensive time-wise, as it usually increased treatment time by another hour, at least. The final straw was a broken file in the palatal root of a maxillary first molar. This case happened to belong to the wife of a good friend of mine and it occurred as I was doing the final shaping of the canal. I couldn’t recall breaking a large hand file in the palatal root of a maxillary first molar in 16 years of endo practice. I swore off Ni-Ti and returned the handpiece. At that point I felt that the risks of Ni-Ti were just too great to justify the apparent “time saving” or “ease of use”.

As a result of my involvement with the Endodontic Internet discussion group ( ROOTS) I gained much needed information about Ni-Ti instruments, their proper use and how to avoid breakage. Dr. John McSpadden’s response to the group’s questions about breakage was especially helpful.

I eventually decided on purchasing Tulsa’s GT Profile series used in an Aseptico DTC motor. The torque control feature was helpful for those of us who needed “training wheels” and wanted minimal risk of breakage while we got used to using rotary Ni-Ti. (Many experienced clinicians feel that Torque Control is not necessary and turn off this feature.)

During the past few months I have begun to incorporate these instruments in my cleaning and shaping routine. I still negotiate all canals to a size #15 to the apex before using them.( I never have been comfortable with the pure ” Crown Down- Apex Last” technique.) My Tulsa representative has been very helpful in assisting me with my initial use. He emphasized the need to use proper lubrication ( I am using RC prep and NaOCL), proper sequence and minimal pressure. The reduction in breakage has been dramatic and the results quite amazing. The most important information that resulted in reduction of breakage of the files was the need to constantly CLEAN THE FLUTES of the instruments during use. This is critical because it is the clogged flutes that increase the “relative contact area” of the file with the canal space. This increased contact area lessens the cutting efficiency and results in stresses than will break the file.

Another interesting bit of information that I obtained from the ROOTS Summit II in San Diego was the opinion of Dr. Steve Buchanan (developer of the Tulsa Profile instrument series). He was adamant in his belief that these instruments should only be used ONCE. His exact quote was ” The savings in time that result from proper usage more than make up for the increase in cost. If you use instruments more than once, DO NOT USE MY INSTRUMENTS.” This presents most clinicians (especially General Dentists with limited treatment fees) with a dilemma. They wish to control their overhead costs but find that discarding the instruments after one use financially impractical. Just how many times can you “safely” use these instruments? THAT is a very good question that remains controversial. Most experienced clinicians say that it depends on the tooth and how much stress ( ie/ curvature, canal size, number of canals etc.) the file undergoes during use. The best rule to follow is the standard rule for Endodontic files of any type: “When in doubt, throw it out.” If I have a case with a tight canal or difficult curve, I follow Buchanan’s advice. They’re gone.

Some time later, Drs. Ruddle and West had been advocating the use of the Tulsa ProTaper system. These files have different varying tapers along their length. I may eventually moved to these once I have sufficient experience. Kerr Sybron’s new K3 files had also become quite popular, and gained general acceptance and positive reviews form those on the ROOTS forum.

In conclusion, I believe that metallurgy and instrument manufacturing techniques had finally caught up with the concepts of endodontic shape and flow. We now have instruments that, when used properly, can negotiate curves and anatomy that were impossible only a decade or so ago. With the addition of heat treatment and better metals, these instruments are now incrdible flexible and resistant to breakage unless severely abused or reused too often.

Proper use of Ni-Ti instrumentation has made endodontics much less tiring on the hands, more efficient and precise. Better shaped canals mean better irrigation and cleaner canal systems. More conservative preparation has made for less compromised dentin and stronger Endo treated teeth.

The basic endodontic concepts for the classic endodontic preparation have not changed but the rotary Ni-Ti revolution has allowed us to achieve these results more easily. My conversion to Ni-Ti rotary instrumentation was complete.