Noting the Unique Advantages of 30o Oscillating Reamers

?Separated instruments were never really an issue until the introduction of rotary NiTi. Yes, a dentist might manually over rotate a K-file in a canal with a sharp bend and break the tip off, but this is a fairly rare event and easily preventable by adhering to short arcs of motion when advancing the instrument manually through the length of the canal. It was only with the deployment of techniques that incorporated full and repetitive arcs of motion that separation became a serious issue. Given the present state of endodontic instrumentation, I think we can make some general statements about arcs of motion and the tendency for separation.

The greater the arc of motion the greater the stresses placed upon the instruments. The greater the arc of motion the greater the need for more flexible instruments. The greater the arc of motion the less control the dentist has over its actions in terms of staying within the confines of the original canal anatomy and remaining intact. That last statement can easily be challenged by the many examples of rotary NiTi clearly shaping canals in accordance with the original canal anatomy at least in the mesio-distal plane and three-dimensionally in canals round in cross-section. What should be understood, however, is that it took the development of flexible NiTi and its further refinement via heat treatments to produce a metal that could adapt to the curvatures of canals without distorting them and to do so through multiple full rotations while being increasingly resistant to torsional stresses and cyclic fatigue.

?Presently, the most advanced NiTi metallurgical treatments have not yielded an instrument that is virtually immune to separation illustrated by a recent post that I placed regarding a poll taken of dentists who clearly still consider separation a major issue and tie the amount of separations they incur directly to the amount of endodontic procedures they perform. It is for this reason that all the original precautions recommended for the safer usage of rotary NiTi are still necessary, including staying centered, most often single usage, straight-line access, crown-down preparations, a light pecking motion, greater enlargement of the glide path in the presence of high resistance and ultimately case selection. One can easily interpret the imposition of all these precautions as a challenge to the easy control of their usage.

Now let’s talk about an operating environment that is the opposite of full rotations where the shorter the arc of motion the less the stress placed upon the instruments. The less the arc of motion the less the need for more flexible instruments as demonstrated by the balanced force technique and 30o engine-generated oscillations. Indeed, rotary developers noted this fact as evidenced by the introduction of reciprocating systems that interrupt full rotations to alleviate the potential of excessive stresses being encountered. Within short arcs of motion 30o oscillations have been proven to virtually eliminate instrument separation when employing stainless steel twisted K-reamers both unrelieved through a 10/02 and relieved with a flat along their working length from 15/02 onwards through a 40/02.?

With the virtual elimination of instrument separation, the dentist is not limited to the centered shaping imposed by rotary systems (both continuous and interrupted). I have attempted to show the ability of engine-driven oscillating reamers to better debride and cleanse the canal systems via cross-sectional studies before and after obturation. That concept has been challenged stating that oscillating reamers will simply move the shaved dentin around within the canal without effectively removing it from the canal, a notion that is easily disproved by observing the debris carried coronally as the instrument is withdrawn from the canal and the fact that the larger subsequent instruments go to the apex with little resistance. The vertical flutes on a reamer unlike the horizontal flutes on a file tend to bypass any residual debris in the canal as the next larger instrument is introduced.

The most compelling data I believe is the video I made of a transparent 3D printed tooth that accurately simulates a mandibular molar including a mesial root with two canals and an isthmus connecting both canals for a major portion of their lengths. This video clearly shows the ability of the high frequency oscillating reamers to not only widen the mb and ml canals, but to effectively cleanse the isthmus connecting the two, something rotary users are not likely to do with the vigor I can apply to these instruments, emphasizing the reason I can do this is because I am virtually assured that the instruments will remain intact despite their vigorous lateral applications.?

Of equal importance is to note the shape of the canals after obturation. The main mesio-buccal and mesio-lingual canals were wider than the isthmus from the start. The final preparation of these two canals reflects that fact. A uniform removal of tooth structure means that relatively speaking the final preparation reflects the original canal anatomy in larger form. To widen the entire space to the same dimensions would be counterproductive and dangerous because it would overly prepare the isthmus area where a concavity is present on its furcal side and potentially at worst lead to strip perforation and at best needlessly further thin out an area that is bound by far less dentin with a greater chance of inducing dentinal micro-cracks.

By employing the 02 tapered stainless steel twisted reamers confined to a 30o arc of motion we have excellent control over the instruments. Although stiffer than NiTi, they are more than sufficiently flexible when confined to short arcs of motion and will remain faithful to the original canal anatomy with the additional advantage of being virtually immune to separation. It is of significant importance that we are not using K-files. The relieved K-reamers are more flexible than comparably sized K-files and the incorporation of a flat along the entire working length from 15/02 through a 40/02 makes them even more flexible than their file counterparts while reducing the engagement and resistance they encounter as they travel apically.?

The balanced force technique is manually applied and consequently hand fatiguing. The same goal of non-distorted shaping is achieved far more quickly and easily using the 30o oscillating handpiece with both unrelieved and relieved stainless steel twisted reamers. Unlike balanced force, 30o oscillation is totally amenable to the 30o oscillating handpiece making it a common sense and improved substitute over their manual use. Now given the efficiencies of 30o engine-generated oscillations, the question is whether or not final canal shaping needs to be done with rotary NiTi. My use for rotary NiTi is now limited to an instrument that will smooth the mesial and distal walls of a canal and size it to fit a corresponding gutta percha point. Even with this limited use, the final rotary instrument, never larger than a 30/04 is not the last instrument in the canal. Knowing that rotary produces both a smear layer and impacts dentinal shavings removed mesially and distally into the broader, but thinner bucco-lingual dimension, I routinely remove all the debris using irrigants combined with say a 25/02 relieved oscillating reamer. I am now ready for obturation.?

The unique advantages of 30o oscillations are realized when combined with K-reamers, a tool that was historically considered inferior to K-files for reasons that I have still not fathomed over the past 50 years or so. Combining 30o oscillations with K-files would prove counterproductive impacting debris apically and too often losing length abolishing the concept of 30o oscillation as non-productive wayward path. Yet, with the introduction of rotary, the use of instruments with reamer designs came into full bloom. Yes, the flute orientation of every rotary system used today (with the exception of the original Profile instruments) is that of a reamer. The reason is obvious. Rotation incorporates horizontal motions and, as anyone knows who shaves, to be effective the shaving blade must be more or less at right angles to the plane of motion. That only happens when the orientation of the flutes are those of a reamer and not the highly horizontal orientation of a file.?

Once we understand the compatibility of 30o oscillations and stainless steel twisted reamers both unrelieved and relieved a cascading of beneficial effects are now realized and endodontic instrumentation becomes simpler, safer and a heck of a lot less expensive.

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Regards, Barry