When Conventional Endodontic Wisdom Is Challenged By Reality
An interesting phenomenon takes place when conventional wisdom is challenged. Those with vested interests may feel a bit less secure. Think of program administrators who have committed to rotary systems. They want to know that their choices were correct, that their choices represent the safest and most effective way of performing endodontic procedures, that their decisions reflect on their wisdom in making these choices. And they represent the second tier of reactions, those that the manufacturing companies have convinced to implement their systems. The companies themselves are always on guard against what they conclude might be sources of challenge and particularly so if those challenges strike at the heart of their selling points. Together the first and second tiers have a stake in undermining any challenges that sow doubt regarding the dominance of their choices.
So let’s examine some of the challenges regarding rotary endodontics whether performed in a continuous or interrupted (reciprocating) fashion.
1. They are more prone to separation. Continuous and interrupted rotary motion leads to a greater incidence of encountering excessive amounts of torsional stress and in curved canals cyclic fatigue, the two factors most responsible for separations. The manufacturers and those who use their products don’t deny that separations can occur, but then insist that proper utilization diminishes that possibility, that it is incumbent upon the dentist to employ all the safeguards to assure their usage within a framework that does not expose them to excess stresses, including rapid replacement that in a practical way underscores their vulnerabilities. If they were not so vulnerable there would be no need to replace them so rapidly.
2. To reduce separation, techniques have been introduced to minimize the resistance any given rotary instrument encounters. These include straight-line access and crown-down preparations both of which exchange the sacrifice of more tooth structure to reduce the stresses the rotary instruments face. Centered shaping, confining preparations to the widest portion of the pulpal anatomy, reduces the stresses the instruments encounter. Another way to reduce stresses is to prepare the canal to smaller dimensions and tapers. Smaller lesser-tapered rotary instruments encounter reduced resistance and are consequently less likely to incur excessive stresses. However, in view of centered shaping, buccal and lingual extensions of pulpal tissue as well as thin isthmuses are often not touched by the instruments leaving that tissue and any bacterial associated with them untouched. The manufacturers and their advocates say this problem is solved by the irrigants, but again challenging this notion are studies that demonstrate that the use of greater tapered instruments actually impact the dentinal shavings removed from the mesial and distal walls into the buccal and lingual pulpal spaces that act as a barrier to effective irrigation further reducing effective cleansing in systems reliant on rotary instrumentation.
3. Rotary instrumentation produces dentinal micro-cracks. The manufacturers and their advocates refute this conclusion stating that the research showing these results are flawed and cite other research that demonstrates a lack of cause and effect associated with rotary instrumentation. Yet, as I have referred to several times in posts, Newton’s Third Law of Motion states two interactive bodies will have an equal and opposite effect on each other, the two bodies being the instruments and the canal walls. It is clearly established that rotary instruments can separate, not that they will, but they can even when all the precautions are taken and that true to Newton’s Third Law the opposite reaction of a separated instrument are dentinal micro-cracks. Given the similar fatigue values of dentin and the metal composing the endodontic instruments, similar reactions are predictable. Newton’s Third Law is a two-way street, not the one way implied by research denying the production of dentinal defects via rotary instrumentation.
Bringing up these three points does not produce merit badges in the eyes of those who have a vested interest in the dominance of rotary procedures. It potentially offers challenges to those who have accepted not only accepted rotary as the superior technique, but challenges the way these techniques are employed. Many of the posts that I have written are not a challenge to rotary. Rather, these posts challenge the way they are incorporated to perform a thorough job of canal cleansing. Below are the steps I employ to enhance the safety and effectiveness of rotary instrumentation.
1. The creation of a glidepath using unrelieved stainless steel twisted reamers through a 10/02 and relieved stainless steel twisted reamers up to a 20/02. Twisted stainless steel is less vulnerable to separation because the are not exposed to the micro-cracks that can develop when the flutes are machined in.
2. The arc of motion of the reamers is first minimized by employing a tight manual watch-winding motion to the apex followed in most situations by their use in a 30o oscillating handpiece that generates an arc of motion so small that instrument separation is virtually impossible. Think about that, virtually impossible to separate. These thin reamers unrelieved and relieved are more than flexible enough to negotiate highly curved canals without producing any significant amount of cyclic fatigue.
3. Being virtually immune to separation they are used vigorously in the bucco-lingual plane removing any tissue present in isthmuses and narrow extension. In short they have the capacity to cleanse in three-dimensions, something that is not safely designed into rotary’s capabilities. I define the process as uniform “internal routing” providing at least through the glidepath stage a way to produce a canal space in larger form that mirrors the original pulpal anatomy.
4. After glidepath creation it is typical of most rotary techniques to assign the rest of the canal preparation procedure to the rotary system alone. That has proven to be at times fraught with the possibility of instrument separation. Rather than isolating the initial oscillating technique from the rotary, through experience I find it far safer to further employ the indestructible oscillating relieved reamers any time I encounter what I interpret as excessive resistance to the helically relieved rotary system we employ. By widening the canals just a bit more with the oscillating system, employed by the way in three-dimensions, I ease the way for the safe application of the helically relieved rotary system, a step that uses one or two more oscillating instruments, but substantially reduces the time it takes for the rotary instrument to reach the apex.
These are insights I have gained over the years. It is a way for me to be comfortable in employing in particular our rotary system that although designed with a helical relief that reduces engagement and resistance, may still encounter situations where I find it desirable to further reduce the engagement that the rotary instruments will encounter. For me nothing beats the use of relieved reamers confined to a 30o oscillating handpiece.
Perhaps the discussion of these options make those wedded to their particular rotary system have a degree of cognitive dissonance. I think that is a good thing. Most of what I employ comes from the insights research has taught me along with clinical experience. That and a little bit of creative thought and common sense have directed me to the conclusions that I presently have. That could change tomorrow with new and enlightening information. Productive discussions lead us forward and no one should be criticized for legitimate questions regarding the conventional wisdom of the day.
Regards, Barry