Endodontic Innovation: Determined By What Came Before It

?We like to thing of progress in a linear fashion, from less sophisticated to more, addressing challenges with ever-increasing specificity leading to more easily achieved superior results. Where endodontic instrumentation is manually fatiguing, the introduction of engine-driven systems mitigates that problem and is defined as progress. Where hand instrumentation, limited by the fatigue it produces often results in inadequate shaping, the additional introduction of highly flexible NiTi coupled to engine-driven systems creates greater tapered shapes that provide increased spaces for gutta percha and the sealer, far more impressive on x-rays.?

Given the limitations of manual instrumentation, it becomes obvious why greater tapered rotary instrumentation became so popular; far less hand fatigue, greater procedural speed, more impressive obturation results. These improvements are so impressive for many dentists that they are the dominant choice despite their vulnerability to separation, need to stay centered and their recommended replacement after single usage. This is the way endodontic innovation evolved and with no further inputs the way it would have remained.

To disrupt the present day logic that validates the leap from manual instrumentation to greater tapered rotary instrumentation, let’s consider the impact if stainless steel twisted reamers generated by a hand piece that produces 30o??oscillations at 3000-4000 cycles per minute had been the dominant system rather than a manual one. Hand fatigue would not have been an issue. The procedural time needed would be far less allowing the dentist to shape canals to larger dimensions that would then be more impressively obturated. Oscillating reamers would have solved the problems that dentists face when they shape canals manually. Those employing this system would not be subject to second thoughts based on instrument separation, something intimately related to rotary NiTi. These oscillating reamers virtually immune to breakage can be used several times with eventual dullness determining when they should be replaced dramatically reducing the procedural costs for the dentist.??

While clinical usage of rotary requires their cautionary usage to prevent separations, those employing 30o oscillation, learning and experiencing just how invulnerable they are to breakage, can and should use them vigorously and uniformly against all the canal walls producing shapes that mirror the original canal anatomy in larger form. From a simplicity point of view, the virtually total resistance to separation gives the dentist a degree of freedom that makes the procedures far less stressful.?

Comparing oscillating reamers to greater tapered rotary NiTi highlights oscillation’s advantages, but that is obvious only because rotary was introduced prior to the introduction of oscillating reamers both unrelieved and relieved. If oscillating reamer canal preparation had been introduced first, the qualities that rotary introduced would have been far less attractive given that dentists would have already had an answer to hand fatigue, excessive procedural time requirements and often times inadequately prepared canal spaces. Furthermore, the whole array of precautions that are necessary to minimize rotary separation would have never occurred eliminating a compensating endodontic history that has only added to the burdens of instrumentation, including the correlation of rotary instrumentation with the production of dentinal micro-cracks that can coalesce and propagate into full blown vertical fractures.?

The limitations of rotary NiTi discussed in this post are verified by the recently modified use of rotary NiTi. Today, they are used far more conservatively generally imposing a taper no larger than an 04. We see and have been discussing minimal preparation as the new model for proper rotary instrumentation. Where many of the rotary systems first introduced included 10 or more instruments, today the newer systems rarely exceed three instruments and often only one. Furthermore, many are used with what I call interrupted rotations, otherwise known as reciprocation. These modifications came about because the manufacturers noted the resistance, as measured by sales, to the expenses associated with systems employing a large number of instruments, the increased incidence of vertical fracture associated with the aggressive removal of dentin and the always present threat of instrument separation.?

With oscillating stainless steel relieve twisted reamers able to shape curved canals without distortion to a??40/02 if need be, the gap between glide path production and final canal shaping has shrunk considerably. The dentist now has the means to routinely eliminate the exposure of any instrument to excessive stresses leading to breakage. Yes, if the canal is opened to a 40/02 by stainless steel relieved 30o oscillating reamers it is important to do so in a sequential fashion using the reamers in .05 mm larger gradations so the next instrument in the sequence can easily follow the increasingly defined pathway that prevents canal distortions. In short, it would be poor technique to jump from a 15/02 preparation to a 40/02. That would lead to distortions.

Understanding the full potential of relieved stainless steel reamers driven by a 30o oscillating handpiece has clarified my use of greater tapered rotary instrumentation. I’ll use the rotary system we developed, NiTi reamers that incorporate a helical flat along their length to reduce engagement and resistance and provide for negotiation to the apex with fewer rotations reducing both torsional stress and cyclic fatigue, but I never lose site of the fact that rotatation is the most important factor in instrument separation because given complex anatomy it is easy to exceed the elastic limit of NiTi when used in this mode. So, give me fairly loose straight conically shaped canals and I will employ our rotary system with minimal trepidation. Give me more complex anatomy that results in significantly greater resistance and I will either modify the canal space first with oscillating stainless steel reamers followed by our rotary system or I will take the path of greatest safety and simply shape the entire canal space using oscillating stainless steel relieved reamers.

The advantage of the relieved reamers is their relative reduced engagement with the canal walls. At any given moment, they will remove less dentin than K-files simply because they contact the canal walls less. This is a plus not a minus. The rapid oscillating motion compensates for the small amount of dentin removed with any one stroke by having a high frequency of strokes per minute. High frequency coupled to an instrument design that engages the canal walls less is a good strategy to shape canals in three dimensions as has been demonstrated in the number of cases that I have posted over the years and the ones that I will post in the future as I get back to work following recuperation from my back surgery.

My father, a dentist, used an old expressions stating, where you’re seated determines how your feet are hanging. We were seated with rotary NiTi and it determined to an excessive extent the path we have had to travel to get to a more rational approach. It’s taken about 25 years to date. Today we know that so much of what rotary first introduced complicated matters. We just didn’t know it at the time because we thought our only other option was the manual use of K-files. That is no longer the case.

Regards, Barry