The Sum of All Data In Evaluating An Endodontic Instrumentation System

My critic has posted a paper that concludes that rotary systems clean canals better and with less distortion than the 30o oscillating stainless steel reamers. He states that this evidence should put the debate to rest, much as he states that the cadaver study on micro-cracks proves rotary instrumentation does not induce dentinal micro-cracks. Whatever weaknesses rotary has be it used in a continuous or interrupted fashion are minor inconveniences that rarely occur and in any comparative study are far superior to the oscillating reamers.

If we discount any marketing motivations he has in proclaiming rotary’s superiority we still have data that throws some doubt on his conclusions. The most convincing data in my opinion is the video of the mesial root of a printed 3D mandibular first molar being what appears to be thoroughly debrided of the simulated pulp tissue including the mb and ml canal as well as the isthmus space common to both canals as shown below.

Please note the final fill where there are no voids in the isthmus area as well as along the length of the canals.

This result contrasts strongly with the multiple studies that have documented inadequate debridement of oval pulpal configurations as well as thin isthmuses particularly in curved canals when employing rotary NiTi. This result should not be surprising considering that one of the main precautions to prevent rotary instrument separation is to stay centered and not deviate from the straight-line access. As has been documented in multiple studies, this precaution results in inadequate debridement as is evidenced in the micro-ct scans below of rotary instruments literally not contacting the majority of the canal walls.

Please note that the bluish-green material is the untouched pulp tissue that is left behind. I include a typical study verifying the poor debridement resulting from the rotary instrumentation of oval canals and thin isthmuses.

Of additional relevance are the cross-sections I have shown and am again showing below of highly oval canals completely debrided without any apparent residue of missed pulpal tissue or bacteria.

The results attained in these two data points result from the basic fact that confined to 30o arcs of motion the instruments are virtually immune to breakage allowing them to be vigorously applied to all the canal walls with the relieved stainless steel reamers oscillating at a rate of 3000-4000 cycles per minute or about 60 cycles per second. That represents pretty good activation of the irrigants that are driven into intimate contact with the canal walls by the vigorously applied reamers. Rotary can do neither as the canal anatomy becomes more complex, an issue 30o oscillating does not have to contend with.

A third data point are micrographs from a French study that clearly describes superior debridement throughout the length of the canals using the oscillating reamers compared to 3 rotary systems. The micrograph demonstrates that the oscillating system was the only one that resulted in open dentinal tubules along the length of the canal.

Laurent Scherman, Patrick Sultan. Comparison of the canal wall states between a mechanized system and various rotary NiTi systems. Le Chirurgien Dentiste de FranceNo. 1411 du Novembre 2009.

Together these three data points contest the results of the study my critic is posting. The results attained in this study makes me question the protocol with which the instruments were used. Did they lean them against all the canal walls vigorously, something rotary is unlikely to do particularly in canals of increasing complexity? Did they use the three stiff NiTi greater tapered files that we no longer employ in the 30o oscillating technique? If they did either, the study does not account for the way the instruments are used today.

Using our present techniques I have posted many highly curved cases that do not appear to produce any obvious distortions, something that is entirely consistent with the relieved stainless steel reamers confined to short arcs of motion. I believe my response to the negative results in the paper my critic has posted are reasonable. To date, not one research paper has been posted on outcomes correlating whatever superior claims rotary studies make regarding degrees of distortion and debridement. What has been published and correlated to inferior results are separated instruments resulting in inadequate debridement of those canals where the separated instrument has prevented thorough cleansing of the canals. What has also been correlated to lower success rates is inadequate debridement leaving voids in the obturation of canals where leakage is now a greater possibility. Leakage and residual bacteria are two documented factors that reduce positive outcomes.

Every time I posted the video showing superior debridement using the 30o oscillating reamers, he immediately focuses on a small amount of apically extruded debris stating that it is unique to the oscillating system. Not only is that statement undermined by a general reading of the literature on this subject, but to illustrate his inaccurate assessment please look at the video below that shows the production of apically extruded debris from a rotary system.

Interestingly, while the various rotary companies are competing amongst themselves to develop instrumentation systems that are less prone to breakage and incorporating more conservative preparations that reduce such events, further reducing their effectiveness in three-dimensional debridement in the process, the 30o oscillating system simply because it is invulnerable to breakage supplies an effective answer to the shortcomings of rotary NiTi that have yet to be overcome when employing rotary NiTi.

As a final thought, the fact that the oscillating reamers are immune to breakage is the reason they are far less likely to induce dentinal defects that over the long run are associated with a higher incidence of vertical fracture. My critic says that issue has been laid to rest except for the fact that it is inconsistent with Newton’s Third Law of Motion that states two interactive bodies have an equal and opposite impact on each other. According my critic that means that while the canal walls can inflict damage to the instruments leading to instrument separation, the instruments have no impact on the canal walls, something, in fact, documented in hundreds of studies, but according to my critic all nullified by the cadaver study. He should tell that one to Newton.

Regards, Barry