Dental Tribune USA

Is rotary NiTi the new paradigm?

By Dr. Barry L. Musikant, USA
March 02, 2011

Does rotary NiTi deserve the title of a new paradigm? The definition of “paradigm” states that it represents a new fundamental model. In the case of endodontics, this new model of instrumentation differentiates itself from the old model by being employed in a crown down fashion rather than the traditional stepback used with K-files.

Those supporting the benefits of this new model state that crown-down has the advantage of pushing less debris periapically, making endodontics more predictable. There is little in the endodontic literature that supports this viewpoint.

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Furthermore, the crown down technique is used with rotary NiTi to minimize the engagement along length, making rotary NiTi somewhat less vulnerable to breakage, but at the same time requiring an increased amount of time for recapitulation. The introduction of a new model constituting a paradigm shift not only implies superiority of the new model, but clearly defines the old system as inferior, out of date and lacking the fundamental intelligence that is incorporated into the new model.

What is most peculiar about this paradigm shift is its dependence on the old model. Rotary NiTi cannot be used unless the glidepath is first created using the K-files.[1] Realizing that the new model is dependent upon the old model leads to some possible insights. The shortcomings of the old model are still present and the new model at best does not add to the old model’s shortcomings. Rotary NiTi, however, does not come without its own shortcomings. K-files, for all their limitations in apical negotiation, non-distorted shaping, impaction of debris and loss of length, rarely broke during usage. Rotary NiTi, on the other hand, has made the dentist constantly aware of its vulnerability to torsional stress and cyclic fatigue, stresses that routinely occur when shaping with rotary NiTi.

An automated rotating crown down approach to shaping canals that is still dependent upon the poorly designed K-file is really a dual system of canal shaping with each portion of the system compensating for the weaknesses of the other. The K-files engage the canal walls excessively, producing a poor tactile perception of what the tip of the instrument is encountering. This limitation can lead to ledging, blockages and apical transportation. For this reason, their use is limited as much as possible before employing rotary NiTi.

Those using rotary NiTi must use the K-files enough so a clear pathway exists from the canal orifice to its apex because the tip of rotary NiTi instruments is vulnerable to breakage if its tip locks and bind apically. It is only when the canal pathway is completely clear along its entire length that the rotary NiTi instruments can be used without fear of torsional stress. A clear pathway does not eliminate all the stresses that rotary NiTi will bear.

Rotation around a curve creates cyclic fatigue, shortening the life of the NiTi instruments, with cyclic fatigue accelerated the greater and the more abrupt the curve being negotiated[2]. Compensation for this vulnerability comes in two forms. The poorly designed K-files (Fig. 1) may be used to further shape the canals before switching to rotary NiTi or the NiTi instruments may shape more conservative preparations, not based on the biologic needs of the canal, but the metallurgic limitations of the NiTi instrument.

Perhaps the best way to illustrate the sleight of hand that has occurred in the marketing of rotary NiTi is to consider a simple alternative: the use of relieved reamers rather than K-files, instruments that work so well that they can be used from start to finish. Whereas K-files engage when a watch-winding motion is used and only remove dentin on the pull stroke, the reamers with half the number of flutes and twice as vertically oriented will efficiently cut the dentin using the same watch-winding stroke.

These instruments engage less along length, are significantly more flexible and cut more efficiently. As long as patency is maintained, these instruments will remain centered when being negotiated apically and have the ability to work all the walls upon withdrawal of the instrument.[3] For the most part these instruments do all the shaping. It is not a dual system because there is no need for another system to compensate for any weaknesses. The strengths that relieved reamers (Fig. 2) bring to shaping canals whether used in a manual watch-winding motion or in a 30-degree reciprocating handpiece remain throughout the entire procedure (Fig. 3).

Fascinatingly, one could say that it is the use of relieved reamers that sets a new paradigm, but that is not strictly the case. Reamer-designed instruments have been around for years, but were never appreciated for their effective design. This is understandable because they have rarely been taught in the dental schools.

Somewhere along the way, K-files became the instrument of choice in institutions of higher learning and so it became ossified over the years without rhyme or reason showing its face. It was really the advent of rotary NiTi that eventually highlighted the shortcomings of K-files. That a system as expensive and vulnerable as rotary NiTi is dependent upon initial instruments of such poor design eventually makes one realize that the edifice of endodontics based on K-files is unsupported. To be dependent upon an irrational design makes no sense.

If we simply brush away the use of K-files, the subsequent use of rotary NiTi and all the marketing that has gone along with its establishment as the new paradigm, we are left with simple, inexpensive yet highly effective tools that allow endodontics to be performed with none of the procedural stress associated with K-files. The world of relieved reamers provides the dentist with the following advantages:

  • Are virtually invulnerable to breakage.
  • Can be used six to seven times before replacement.
  • Even if used inadvertently many more times will still not break.
  • Negotiate apically with far less resistance than K-files.
  • Are more flexible, less engaging and more effective at removing dentin from the canal walls than K-files.
  • Do not snap back to the straight position like rotary NiTi (Fig. 4).
  • Record curvatures.
  • Instruments that are confined to a tight arc of motion 9. Instruments that stay centered when negotiating apically and can be used against any and all walls when being removed from the canals.
  • Can differentiate between a tight canal and a solid wall (Fig. 5).
  • Can differentiate between a round and oval canal.
  • Can shape even a highly curved canal to a minimum of 35 without canal distortion.
  • Have a cutting tip piercing rather than impacting dentinal tissue and debris.[4]
  • Can be used both manually and in a 30-degree reciprocating handpiece.
  • On average cost 90 percent less than rotary NiTi on a per-use basis.

What any dentist might want to ask himself is whether or not he is listening to the sizzle or tasting the steak. It is amazing how many dentists once they have heard and smelled the sizzle are desperately waiting to experience the steak only to be disappointed with the shortcomings inherent in any rotary NiTi system.

For anyone who has made a major investment in rotary NiTi, it may be difficult to accept the fact that simpler, more effective and far safer means of shaping canals exist today that cost a fraction of what rotary NiTi costs.

These alternative systems don’t have to be called a paradigm shift. It’s not necessary. What is necessary is for the paradigm shift to happen inside of us, letting us have the ability to judge systems based on their performance rather than the promise of that performance.

For examples of cases that highlight the clinically excellent results using the alternative methods discussed in this article, see Figures 6-8.

With that in mind, knowing nothing beats that old adage that the proof is in the pudding, I make my long-standing offer to anyone who wishes to experience the superior effectiveness of relieved reamers over K-files, K-flex files and rotary NiTi to take the free one-on-one two-hour workshop I give in our New York endodontic practice.

If you are interested, call (212) 582-8161 and ask for Evelyn to schedule the workshop, which generally is held on a Tuesday or Thursday from 7 to 9:30 p.m. The address is 119 W. 57th St. — a safe part of town for out-of-towners who may have any trepidation.

About the author

Dr. Barry Lee Musikant has co-authored more than 300 articles in dentistry in various international dental journals. As a partner in the largest endodontic practice in Manhattan, Musikant’s 35-plus years of practice experience have crafted him into one of the top authorities in endodontics.

Editorial note: This article was originally published in Endo Tribune U.S. Edition Vol. 6, No. 1, 2011. A complete list of references is available from the publisher.

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