A Deeper Comparison of 30o Oscillating Reamers To Rotary NiTi In Endodontic Instrumentation

The employment of micro-ct scans has not only demonstrated the complexity of pulpal anatomy, but the inability of rotary instrumentation to adequately debride the canals of the tissue and bacteria that reside within these spaces as their canal configurations become flatter, thinner and more oval. This should come as no surprise given the precautions that are required in their use to prevent instrument separation, among them staying centered within the least resistant portion of the pulpal anatomy. The aggressive application of these instruments against all the canal walls is prohibited lest it lead to a greater incidence of instrument separation.

The result of these precautions is the documented shortcomings of leaving debris (pulpal tissue and bacteria) in the buccal and lingual extensions of oval canals, in isthmuses as well as a variety of flat pulpal configurations that are often present. That problem is further exacerbated by the impaction of dentinal debris that was removed mesio-distally using greater tapered rotary instruments being impacted into the buccal and lingual confines compromising the dispersing and penetration of the irrigants. These statements are not conjectures. A large body of studies confirm these consequences as canal anatomy increasingly deviates from straight round pulpal configurations.

Despite the clear evidence that such shortcomings are a consequence of rotary NiTi’s vulnerabilities, their negative impact is often not appreciated simply because the quality of treatment is accessed by the presence of a white line to the apex as seen on a periapical x-ray, a two dimensional mesio-distal image that provides little information on the preparation of the canals in the bucco-lingual dimension. Yet, it is debridement in the bucco-lingual dimension that is most compromised by a system that must stay centered to reduce the incidence of instrument separation. That shortcoming is generally ignored simply because it cannot be seen. What is seen is rotary NiTi’s ability to negotiate curved calls with little apparent distortion and it is often quite impressive looking.

One might question why the results of rotary instrumentation are frequently extremely thin preparations, certainly no wider bucco-lingually than they are mesio-distally. One might think that canals often significantly wider bucco-lingually and thoroughly debrided would produce images (white lines) that are wider particularly if the x-rays are taken from a mesial or distal angulation, but that is generally not the case. What these images represent are well-centered preparations to the apex providing a space for the placement of a thin lesser tapered gutta percha point. If as rotary users say, the irrigation systems are cleaning the canals bucco-lingually then a radiopaque cement would produce a broader imagery in that plane. That does not appear to be the case.

The fall back rationalization for these documented shortcomings is that based on success rates whatever documented shortcomings are associated with rotary NiTi, they do not adversely effect outcomes while noting the greater productivity of rotary users compared to those employing the manual use of K-files. As long as the comparison is between rotary NiTi instrumentation and the manual use of K-files, rotary is likely to win despite the concerns of instrument separation. Rotary reduces the time requirements, reduces hand fatigue making the dentist more productive and the procedures less stressful with the glaring exception when instruments separate within the canals. So great are the advantages of engine-driven systems over manual ones, that the concern of separation is outweighed. So dentists accept the reality that an occasional instrument separation may occur. They find the mesio-distal periapical x-ray sufficient proof that the canals are adequately debrided despite documented evidence to the contrary and they live with what they experience as an acceptable success rate which according to the literature in non-vital teeth is about 85%.

Now 85% is not 100% leaving open the possibility of higher success rates with the micro-ct scans suggesting that that may be accomplished with better three-dimensional debridement. Dentists already show by their preferences in purchasing rotary systems that any alternative to rotary must also be engine-driven. No dentist is going to go back to manual after experiencing the advantages of engine-driven systems.

So, for sure, any system that seeks the broad approval of dentists must be engine-driven. But, why change from one engine-driven system to another? As we all know, rotary systems are associated with instrument separation. An engine-driven system that eliminates instrument separation would be highly attractive. How is that accomplished? Rather than having rotary instruments negotiate through canals of widely varying anatomy, have them negotiate through the length of the canal via a handpiece that generates 30o arcs of horizontal motion, arcs of motion that are so small that they minimize the torsional stresses and cyclic fatigue, the two factors that produce separations, to the point where they can no longer result in instrument separation. That is a problem that rotary instrumentation, whether continuous or interrupted (reciprocation) has not entirely solved.

As stated earlier, rotary NiTi requires the precaution of staying centered throughout the preparation of the canal space particularly as the canal anatomy becomes more complex. The short arcs of motion produced by the 30o oscillating handpiece eliminating instrument separation allow the dentist to vigorously apply these instruments against all the canal walls assuring debridement not just mesio-distally, but also bucco-lingually. The 30o oscillating handpiece runs at a frequency of 3000-4000 cycles per minute activating the irrigants that are forced into intimate contact with all the canal walls increasing three-dimensional debridement both mechanically and chemically.

Another precaution traditional rotary NITi instrumentation requires is straight-line access and crown-down preparations both of which necessitates the sacrifice of coronal dentin beyond the needs of debridement. Essentially, rotary uses its largest instruments first to widen the coronal portion of the canal so the subsequent lesser tapered rotary instruments will not encounter as much resistance as they negotiate to the apex. In 30o oscillations, the thinnest instruments are used first in negotiating to the apex. Being the thinnest they encounter the least resistance. They also have the best possibilities of penetrating thin isthmuses and narrow buccal and lingual extensions. They remove far less dentin mesio-distally eliminating the impaction of that debris bucco-lingually that occurs with greater tapered rotary instruments as well as having a far greater ability in penetrating any thin anatomy that may be present along the length and width of the canals.

One way to describe the action of 30o oscillating instruments is “internal routing”, using instruments that are thinner than the canal space, applying them against all the canal walls with the intention of removing a uniform amount of dentin circumferentially resulting in a prepared canal space that mirrors the original cross-sectional anatomy in larger form. Compare this approach to rotary NiTi that if used conventionally removes excessive amounts of dentin mesio-distally and if used in the new conservative fashion with minimally prepared canals results in a further diminishing of debridement in the bucco-lingual plane. Internal routing lets the dentist target far greater portions of the pulpal anatomy than rotary systems.

While the elimination of instrument separation with the consequent ability to instrument three-dimensionally are the most obvious advantages over rotary NiTi, other beneficial aspects should be mentioned. These include the following:

. The complete elimination of hand fatigue in most situations

. 30o oscillation uses stainless steel relieved twisted reamers. K-files are not used because their flute orientation is predominantly horizontal and for the efficient shaving of dentin from the canal walls, the flutes should be more or less at right angles to the plane of motion. The 30o handpiece is generating short horizontal arcs of motion that will shave dentin from the canal walls most effectively when the flutes on the instrument are predominantly vertical. In short, the vertical flute orientation of a reamer is simply a superior design than the horizontal flute orientation of a K-file.

By putting a flat on the working length of the reamers, the instruments encounter less resistance, they are more flexible, they provide an extra space for debris letting them negotiate through the canal more easily. Of significance is the fact that confined to short arcs of motion, the 30o oscillating reamers stay true to the canal anatomy eliminating the potential for distortion. This last quality should be fully appreciated. Rotary NiTi required the introduction of an entirely new metal that over the years has been modified by heat processing to become more resistant to breakage. While separation is less of an issue, it is still an issue with most rotary advocates recommending single usage as the surest way to reduce instrument separation. On the other hand, the stainless steel relieved reamers confined to short arcs of motion, immune to separation, are routinely used several times before replacement. They re discarded when they become dull, not out of fear of separation resulting in great cost savings.

I’ve stated the advantages of stainless steel relieved 30o oscillating dreamers over rotary NiTi in many posts. My goal is not repetition in its own right, but rather my own integrated understanding of how technology that has existed for many decades can lead to superior function compared to NiTi that was originally described as a paradigm improvement over anything else that had previously existed. In short, although combining relieved stainless steel reamers with a 30ooscillating handpiece had not been done before, existing technology that did not require the invention of a new material, it has proven by the parameters we use to judge effective canal preparations to be more risk-free and effective than rotary NiTi.

Regards, Barry