Contradictions in My Critic’s Comments

He states that rotary cleans canals better. That is contradicted by cross-sectional studies of oval canals and thin isthmuses that clearly demonstrate residual pulp tissue and bacteria remaining after the centered shaping of rotary instruments. That data is further confirmed by micro-ct scans that show in even more detail the inadequate debridement of oval canals and thin isthmuses. These results are not surprising. One cannot clean better if one has to stay centered in following the path of least resistance to reduce instrument separation?

He equates 30o oscillation of relieved stainless steel reamers with the watch winding push-pull stroke of K-files and notes the debris extruded apically when using oscillating relieved reamers. The research clearly shows that K-files with their predominantly horizontal flute orientation used in this manner produce the greatest amounts of extruded debris apically. The relieved reamers, with predominantly vertically oriented flutes tend to bypass debris situated along the length of the canal, driving smaller amounts over the apex. Yet, as is the case with all flutes rotational systems (be they large or small rotations) they will produce apically extruded debris.

The flute orientation of the relieved oscillating reamers is similar to the flute orientation of rotary NiTi instruments. They are both used with an up and down motion as they go through their varying amounts of horizontal arcs of motion. With rotary NiTi the up and down motion is defined as “pecking”, but it is still an up and down motion. So, what are the differences between the two techniques?

? Rotary is either continuous or interrupted full rotations while the oscillation reamers?are confined to 30o arcs of motion.?

? Rotary employs instruments with tapers greater than 02 mm/mm in a crown-down fashion. Oscillating reamers are limited to 02 mm/mm tapers immediately negotiating?to the apex.

The research data states that all systems using fluted instruments will produce apically extruded debris. Let’s look at the two approaches in terms of a potential plunger effect. Rotary using greater tapered instruments in a crown-down fashion would appear to create?a greater plunger effect than a lesser tapered thinner instrument. Please visualize the resistance an 06 tapered NiTi instrument encounters as it enters a canal and the potential plunger effect it would have on any fluid and debris?ahead of it that it would encounter as it travels apically within the canal. Compare that visually to an 06 tipped 02 tapered stainless steel reamer that by definition must encounter less resistance than the greater tapered instruments. Less resistance means a reduced plunger action on the fluids and debris that are ahead of the instrument.

Rotary advocates will say the rotating instrument brings the debris coronally as the instruments engage with the canal walls. That is true, but before that action occurs the plunger effect is occurring merely by inserting the greater tapered instruments into the canal. The oscillating reamers have negotiated to the apex with the thinnest stainless steel reamers encountering less resistance, removing significantly less tooth structure mesio-distally and incorporating a reduced plunger effect compared to rotary NiTi. That is not to say that both approaches don’t result in the apical extrusion of debris, something clearly seen in a video I posted. To substantiate this claim, here is a video using one of the latest rotary instruments that results in a similar amount of apically extruded debris.

From my observations, the main culprits in the apical extrusion of debris are K-files and Hedstroms used in a push/pull fashion that accentuates the horizontally oriented?plunger design of their flutes. Vertically oriented flutes whether used in oscillation or rotation (continuous or interrupted) reduce the amount of debris extruded apically. I think it is reasonable to dismiss the use of K-files and their use in the balanced force technique. Yes, it will produce the least amount of apically extruded debris, but it is slow, hand fatiguing and confined?to the centered portion of the canal. In a day and age when manual instrumentation has been increasingly?replaced by engine-driven systems it is unlikely to be employed by the majority of dentists.

So, based on extruded debris alone, rotary cannot claim any advantage. However, from my perspective, the entire discussion regarding the apical extrusion of debris misses the point. And to repeat once again, that point is 30o oscillations eliminate instrument separation, not reduces it, eliminates it. And from that single benefit, a cascading of beneficial properties become available to the dentists, including:

? The ability to vigorously apply the stainless steel relieved twisted reamers?against all?the canal walls resulting in superior three-dimensional debridement.

? Non-distorted shaping resulting from the stainlesss steel relieved reamers being

?applied to the canal walls with short arcs of motion.

? The reduction in the production of dentinal micro-cracks associated with rotary NiTi, a controversial issue that has been confirmed in the most recent studies on this subject.

? Reusability-instruments that don’t break can be used multiple times.

? Reduction in procedural stress knowing the instruments will remain intact.

These are substantial benefits that give the dentists the freedom to utilize these instruments for their original purpose, non-distorted three-dimensional debridement. Challenges to these claims include not accepting data remitted to support these claims as well as ongoing personal insult. I suppose referring to issues that expose the weaknesses of rotary NiTi can lead to a degree of cognitive dissonance for rotary users. After all the goal is to do a good job and the stated compromises that rotary engenders is not a positive feeling. Nevertheless, critical analysis is the only avenue to progress and while such analysis may be uncomfortable, the alternative is to be ruled by the status quo which states that we live in the best of all possible worlds and advancement is really only destabilization of what is already ideal. That was the state of mind before the age of enlightenment and does none of us any good if we ever revert back to that mind-set.

One might think that I would eliminate the use of rotary completely. That is not the case at all. From my perspective it has 2 distinct benefits. It smooths the canal walls in the mesio-distal plane for a better look on x-ray and sizes the canals mesio-distally for the fit of the appropriate gutta percha point. These 2 functions, however, don’t require a series of rotary instruments. They require only one final rotary instrument after 98% of the canal preparation has been attained using the 30o oscillating reamers.?

Used in this fashion, the single rotary instrument is exposed to minimal resistance eliminating the incidence of separation due to excessive torsional stresses, cyclic fatigue or both. The resistance is further enhanced by using a helically relieved rotary instrument we developed?that encounters less resistance as it negotiates to the apex. If on the outside chance, the rotary NiTi instrument still encounters what I perceive as excessive resistance, on these rare occasions?I will simply further enlarge the canal preparation with a larger oscillating stainless steel reamer that does any with the excessive resistance the final rotary instrument encountered.

Please note, that in the instrumentation technique we advocate rotary NiTi is relegated to an accessory position. It is not the main tools to be used. For me, those are the oscillating reamers for all the reasons stated above.

When I look back on how I came to evolve into the positions I presently have, it stemmed from my first utilizing?rotary for all the claims made for it, but then made uncomfortable and insecure?due to its unpredictable incidence of separation as canal anatomy becomes more complex. That I was now employing a system that was far more expensive while making me worry more was enough motivation for me to find better solutions for what I was using at the time. Such is the path that I have been on for about the last 30 years. I enjoy sharing whatever insights I’ve gotten as well as the constructive feedback from all the dentists we have taught over the years.

Regards, Barry