The Purpose Of A Broad Discussion On The Mechanics Of Endodontic Instrumentation

Let’s first state that the profit motive in any discussion is always going to be present in terms of convincing dentists to buy into one technique or another. Having said that a critical review of the various techniques is what is relevant and any personally degrading remarks are not only irrelevant, but an attack on the core concepts of an unbiased education.

Where does a critical review start? There are undoubtedly many ways to introduce critical thinking. For me, it starts with my personal experiences and the negative events that occurred during endodontic instrumentation. The most negative event and the one most noticeable, the two seem to go together, is the separation of an instrument in a canal. That event in my experience is most consistently associated with rotary NiTi and is a major factor in the stress I encountered. That such events are not limited to me personally, are documented by the hundreds of studies still being published to this day that confirms this unwelcome downside of rotary NiTi instrumentation as well as the comments made by the dentists who take our workshops who are seeking methods that avoid this particular iatrogenic event.

The problem of instrument separation particularly due to its obvious presence on x-ray is one that seeks a solution. Instrument separation results from repetitive full arcs of motion. Instrument separation is reduced, but not eliminated by interrupting these full arcs of motion using a non-linear reciprocating motion that still produces full arcs of motion, but takes a few cycles to achieve. The greater the complexity of the canal anatomy the greater the chances of instrument separation. All this has been amply documented as stated above in hundreds of articles regarding the causes of instrument separation.

One effective full proof solution is to limit the arc of motion to 30o or 1/12 of a full arc of motion. The shorter the arc of motion the less stress the instruments encounter regardless of the complexity of the canal configurations they are negotiating through. At 30o the stress is so attenuated that stainless steel relieved reamers are virtually immune to separation, again, regardless of the complexity of canal anatomy. This insight is not trivial. It is a solution to rotary NiTi’s greatest shortcoming. The insights that the 30o oscillations are produced most effectively by using a 30o oscillating handpiecce that can be operated at frequencies generating 3000-4000 cycles per minute that in no way increase the chances of instrument separation were welcomed additions.

The secondary problem that rotary NiTi has results directly from its vulnerability to separation. To reduce the incidence of breakage, the instruments are to be advanced into the canals using a centered light pecking motion with minimal lateral deviations. This is an effective method of debridement in canals round in cross-section, but has been documented in hundreds of studies to leave large portions of untouched canal walls that retain remnants of pulp tissue and bacterial plaques along their length when they have an increasing oval configuration or isthmuses are present. This secondary problem unlike instrument separation is not noticeable on x-ray and consequently is not considered as an important shortcoming to overcome. Yet, it is a direct result of the prime shortcoming of instrument separation.

With these two shortcomings so obviously documented in the endodontic literature, the emphasis on the positives of rotary NiTi include it being an engine-driven system that reduces the hand fatigue and time requirements of the manual use of K-files and the greater flexibility of the NiTi instruments that are far less likely to induce distortions in increasingly curved canals. These positive features are emphasized with the goal of deemphasizing rotary NiTi’s weaknesses. Yet, the greater emphasis on an engine-driven system and reduced potential for distortions in no way eliminates the problem of instrument separation.

A further examination of the use of 30o oscillations has illustrated that the stainless steel relieved reamers remain true to even the most complex pulpal anatomy, that confined to short arcs of motion they do not induce canal distortions. Clearly, the implementation of stainless steel relieved reamers confined to short arcs of motion overcomes the distortions and likely separation of instruments were they to be used in full rotations. At the same time, being invulnerable to breakage they are vigorously applied to all the canal walls. There is no need to stay centered to avoid instrument breakage.

In my internal debate, I wondered whether the NiTi instruments could also be used in the 30o oscillating handpiece and would they have any advantages over the stainless steel relieved reamers used in this fashion being more flexible to start with. Given the fact that the stainless steel relieved instruments have been shown to stay true to the original canal anatomy, they also retain their cutting edges better than NiTi providing effective debridement through multiple uses. They are far less expensive to start with and given their ability to be used multiple times further reduce their costs per use.

I define these differences as solutions that I apply in my own endodontic practice, experiences that confirm the effectiveness of the methods I am employing. When it comes to the endodontic literature there is no data that exists that defines one particular way is the best. Indeed, many studies on comparative degrees of distortion, extruded debris, dentinal micro-cracks, degrees of debridement will show superior performance of one system over another. Yet, none of these individual results correlate to higher success rates throwing into question to what degree they should be considered as guides in what to use.

What has been shown to be crucial to endodontic outcomes is the maintenance of patency of the canal systems particularly in non-vital situations. Instrument separation compromises that patency having a negative impact on outcomes when it occurs. That is the elephant in the room and systems that completely overcome that particular shortcoming are worthy of an optimistic critical analysis.

I wrote this particular post to emphasize the need to keep avenues of discussion open. There are those who would like to see these posts end. Admittedly, they are not advertisements for the use of rotary NiTi endodontifcs as the dominant method of canal debridement. Yet, there is nothing personal in these posts, nor should there be anything personal in the responses of those of a different opinion. From the many positive responses I have gotten in regards to the discussions I post, I believe that what I am posting is a positive attempt at making the discussion of endodontic instrumentation more broadly based. For those who disagree, let’s at least continue the discussions in a collegial fashion.

Regards, Barry