Feedback On Endodontic Instrumentation

After 49 years as the founder of a multi-person endodontic practice one of my partners Dr. Doug Kase and I have taken up the offer to join another endodontic group. Retirement is not in the picture and I am looking forward to expanding my in-person teaching efforts by emphasizing the effective safer alternatives to rotary NiTi instrumentation that I have been espousing over these past several years. It will be a pleasure getting away from zoom presentations, something I never really felt comfortable with. In preparation for an increased educational effort, I have recently made contact with a number of dentists as well as other endodontic specialist to discuss their main concerns.?

There were no surprises in those concerns. I knew from past encounters that the fear of separation was always on their minds to the extent that for some that was the reason they gave up doing endodontics completely or limited themselves to all but what they considered the easiest cases. Another concern was the loss of length too often encountered in their initial creation of the glide path. I was totally familiar with these concerns having addressed them myself years ago and in the process finding solutions that overcame these two fundamental problems.?

Interestingly, one young endodontist enthusiastically told me that to overcome separation anxiety, she discards the instruments after a single usage and uses?multiple systems to achieve her goals with minimal chance of instrument breakage. I told her that engine-driven alternatives exist that give her the ability to shape even the narrowest highly curved canals while completely eliminating instrument separation, doing away with practically all hand fatigue, avoiding canal distortions, and allowing their multiple usages. Particularly among specialists, these claims lead to raised skeptical eyebrows, an understandable reaction given the multiple generations of rotary NiTi where such promises never quite confirm the claims made for them.

It is this skepticism more on the part of endodontists, particularly young ones, as well as the limited exposure other dentists, have had that is spurring my interest in expanding my role as a teacher. The method I use to teach the alternative form of endodontic mechanics includes using natural teeth that the participants employ to carry out their tasks. Three-dimension printed teeth as well as canals in plastic blocks are no substitute as a learning tool. Plastic cuts differently providing a tactile perception that does not simulate the real thing. I learned that after years of using these man-made devices they simply do not convey reality, a reality that departs from the plastic substitutes as the cases become more complex.

What constitutes the changes that the dentists are exposed to when they participate in these endodontic workshops? Let me discuss them and then elaborate a bit.

?You’ll learn to use stainless steel K-reamers rather than stainless steel K-files for the initial negotiation of the canals. As I have elaborated in previous posts, there is a significant improvement in canal negotiation when using K-reamers. Why? The reamers have half the number of flutes along their working length, a working length that is the same for both reamers and files. The only way a reamer with half the number of flutes fills the 16 mm of working length is if they are twice as vertically oriented. The opposite is the case for files. For an instrument with twice the number of flutes compared to a K-reamer to fill the same 16 mm of working length the flutes must be twice as horizontally oriented.

What makes more sense, fewer more vertically oriented flutes or twice as many horizontally oriented flutes? To answer that question think about how you typically use the K-file the one most dentists initially employ. Most dentists apply a manual back and forth (watch-winding) stroke followed by a pull motion. The horizontal motion embeds the predominantly horizontally oriented flutes into the dentin without shaving any dentin away from the canal walls. Once embedded the pull stroke then shaves the engaged dentin away from the canal walls and in that way shapes and cleanses the canals. Most dentists have been doing it that way for years. However, with that type of usage loss of length, the result of impacted debris apically is a concern increasing in possibilities as the canals become narrower, longer and more curved. Why is that the case??

While the pull stroke shaves dentin away efficiently because that is the movement that is more or less at right angles to the plane of motion, those same predominantly horizontal flutes along the length of the K-file are ideally designed to impact debris ahead of the instrument when it or a subsequent file is introduced into the canal. Compare that to the mechanics of the reamer where the flutes are predominantly?vertically oriented. The same back and forth motion is now employing a flute design that is more or less at right angles to the plane of motion, the orientation that is needed to shave dentin away from the canal walls. Rather than just embedding the flutes into the canal wall with the first horizontal clockwise motion, the vertically oriented flutes along the length of the reamer shaves the dentin way without the need for the vertical pull stroke. The pull stroke employed with reamers is simply to exit the instrument from the canal so the debris collected in the flutes can be removed. Upon re-entry into the canal, the vertically oriented flutes are designed to by-pass any debris rather than impacting it the way the files are likely to do.?

Using reamers rather than files is likely to reduce the incidence of lost length in the early stages of canal shaping. We obviously want to avoid debris impaction so the rotary instruments that are subsequently employed can negotiate through a space that has been prepared to the apex without any obstacles in the way. It should also be noted that the rotary instruments that are used after the creation of the glide path are all designed as reamers, not as files strongly suggesting that the initial use of K-files is a historic anachronism that has no place in the modern shaping of canals, something I have addressed in previous posts.?

Other advantages accrue in the use of K-reamers. They can be used in the 30o handpiece oscillating at 3000-4000 cycles per minute eliminating practically all hand fatigue and speeding up the instrumentation process. Furthermore, the K-reamer can be modified with a flat along its working length, reducing the resistance the instrument encounters on its way to the apex, making it more flexible and adaptable to curved canals. Now anyone using an engine-driven system is likely to think of rotary and the increased chances of instrument separation and then recognizing that we are employing stainless steel rather than NiTi that the likelihood for distortions in shaping curved canals should increase. Both these possibilities would be true if they were being used with full rotations. That, most decidedly is not the case.

?Confined to a short arc of motion of 30o the instruments are virtually devoid of the torsional stresses and cyclic fatigue that plague rotary instruments. In short, they are virtually free of separations. Of equal importance, the short arc of motion applied with apical pressure has been shown to stay within the original confines of the original canal anatomy preventing the distortions that would occur in curved canals if a full rotary motion were employed. The potential to vigorously use a virtually unbreakable instrument without inducing distortions is now doable giving the dentist the ability to aggressively apply the relieved reamers against all the canal walls assuring a superior cleansing potential compared to a file that may clog the apical portions of the canal with debris or a rotary instrument that is more likely to separate the more it veers from centered shaping.

These are key principles that if implemented will make endodontic instrumentation far more predictable. It is my goal to teach these principles to as wide an audience as possible. Of course there are detractors who wish to defend the status quo and I welcome any input in the form of a collegial debate from them that leads to better techniques.?

Regards, Barry