What is the Real Meaning of Endodontic Innovation?
The word innovation has been applied to the introduction of rotary NiTi, further enhancing it by describing the innovations as paradigm improvements in the endodontic instrumentation of teeth. A combination of increased flexibility, greater tapers, metals increasingly resistant to torsional stress and cyclic fatigue, reduced armamentarium and a reduction in procedural time requirements add to the aura of a new paradigm. From the point of view of well-financed companies, selling a product marketed as a paradigm improvement has tremendous upside. With that goal in mind, research studies have shown that thin conically shaped canals in plastic blocks could be enlarged to greater tapers without deviating from the original curvatures of the canal and that the same results could be displayed in the mesio-distal plane of natural teeth. Combining this research with corporate incentives for dental schools to adopt these systems and the penetration and domination of the market was inevitable.
It has been over 25 years since the introduction of greater tapered rotary NiTi instrumentation. Looking back, we have a chance to critically review the research that was done as well as examining the clinical outcomes produced by this highly touted approach. For me, what first comes to mind, is the original research done on enlarging canals in plastic blocks. A plastic block has little in common with natural canals. The canals in a plastic block start out as thin conically shaped tubes. The greater tapered instruments employed to enlarge them simply stay centered and the result will be a larger version of the original canal anatomy with the taper of the instruments determining the degree and location of the enlargement. The canal located in the center of a plastic block square in cross-section tells us nothing about the impingement of greater tapered preparations on the external anatomy of a natural tooth. No, furcal concavities exist to lend caution to the amount of tooth structure that can be safely removed without incurring strip perforations. Nor does a bulky plastic block give us any measure of the impact of greater tapered shaping on the overall strength of the remaining root structure.
Accepting the undistorted shaping produced by greater tapered rotary NiTi instrumentation based on the results produced in plastic blocks as proof of effectiveness is misguided and ignores the impact of such shaping on the remaining tooth structure, something that understandably is not obvious when using the plastic block model. When research studies use natural teeth, the pulpal configuration is far less likely to be conical having instead a broader bucco-lingual anatomy combined with a thin mesio-distal configuration producing canals that are oval in cross-section. This type of research can show many things including the lack of debridement in the bucco-lingual plane, excessive removal of dentin in the mesio-distal dimension undermining the root in this plane, the vulnerability to strip perforation on the furcal sides of roots. However, this was not the intent of most of this research. The goal was to once again emphasize the lack of distortion that occurs when using these instruments. From that narrow perspective, the studies on natural teeth (limited to an analysis of the mesio-distal plane) duplicated the results obtained from those first done on plastic blocks. The results reinforce the original research and any effects that might be interpreted as detrimental to the final outcome are simply ignored or minimized in the research discussion.
The truth is that the innovation of greater tapered rotary NiTi instrumentation has been shown to come with a great deal of baggage, the most prominent piece of baggage being its unpredictable vulnerability to separation. Much has been written about the steps needed to minimize greater tapered NiTi instrument separation. A few key steps, namely the need for straight-line access and crown-down canal preparation, require the sacrifice of dentin to improve the safety of the instruments. In articles discussing these and other safety steps, it is a given that greater tapered rotary instrumentation is sacrosanct. If one has a problem using these instruments any step necessary to preserve their use must be incorporated even though detrimental to the remaining root structure. It is rare to find an article touting rotary NiTi that anywhere in the discussion considers the possibility of using approaches that don’t require the needless sacrifice of tooth structure to preserve instruments. Such research reinforces artificial limitations on what should be an informative discussion and is more a marketing tool that attempts to define the universe within which we should all operate that coincidentally increases the sales of these products.
The negative impact that greater tapered rotary instrumentation removes excess tooth structure in the mesio-distal plane and inadequately removes pulpal tissue in the broader bucco-lingual plane is now dwarfed by the last 10 years of research that clearly correlates the production of dentinal defects with the use of greater tapered instruments and their use in rotation be it continuous or interrupted. Thinking about this documented research, we are learning that we have a system defined as a paradigm improvement that requires the excess removal of tooth structure for its own safety so it can more easily rotate within the canal that is now increasingly likely to produce dentinal micro-cracks that can coalesce and propagate into full blown vertical fractures.
That vertical fractures have been an increasing concern following endodontics over the past 25 years has been noted with all but the most obvious conclusions drawn by those with vested interests in the continuing success of rotary NiTi instrumentation. The reality is that the financial success of a product reinforces its own continued existence. The schools receive grants from companies selling these products and they continue to teach these techniques. The AAE is sponsored by those same companies and give them prominence at the meetings. It is a quid pro quo and at a certain point in marketing success it takes on the benefits of the status quo, stifling critical analysis and subjecting us to educational experiences that have been highly filtered. The truth is out there, but an effort must be made to go beyond those entities that give us the low hanging fruit that we often think is real sustenance.
Imo, once we employ a system that is virtually immune to separation we no longer need to emphasize straight line access and crown-down preparations preserving significant tooth structure in the process. That system is engine-driven, limited to a 30º arc of motion and employs predominantly twisted stainless steel 02 tapered relieved reamers oscillating at 3000-4000 cycles per minute. With full confidence that the instruments will remain intact, the dentist can take the thinnest 02 tapered stainless steel reamer and vigorously apply it against all the walls of a canal be it round, highly oval with buccal and lingual isthmus-like extensions. The anatomy is no longer an impediment to full circumferential cleansing. It is the anatomy itself that directs the instrument without any limitations based on concerns for safety.
It is highly likely that the mesio-distal taper of the canal will be minimal and clearly no wider than an 04 while the far broader bucco-lingual dimensions could easily produce a much greater taper. In both dimensions, limiting the arc of motion to a non-rotating 30º gives the dentist the ability to produce the different but appropriate tapers with nothing more than an 02 tapered instrument in tight canals and nothing greater than an 04 taper in most canals. Confined to 02 tapers, many canals can be opened to a 40 apically providing a space for effective irrigation and at the same time sacrificing minimal dentin coronally. For example, a canal prepared apically to a 40 (worked aggressively against all the canal walls) will have a mesio-distal preparation of .64 mm 12 from the apex. Compare that to an 04 tapered instrument opened apically to a 30. 12 mm coronally the mesio-distal diameter is .78 mm or 22% wider. The preparation is wider coronally despite an apical preparation .10 narrower. I prefer a greater apical preparation because it is apical where the greatest incidence of pulpal branching occurs with a wider preparation providing greater space for effective irrigation.
Whether the canals are narrow and tortuous, of medium complexity or extra wide as seen in younger patients, the 30º reciprocating approach is easily adaptable to all these situations. Over the years, I have never assumed that any particular case is too difficult for most general practioners. My viewpoint has changed in recent years as we as specialists are asked to do more retreatments, handle cases with broken instruments and inadvertent perforations as well as highly calcified teeth on patients with compromised health issues. GPs are more than capable of doing the majority of endodontic cases. However, I would think twice before tackling those cases where the canals are highly curved or barely seen on x-ray. They can lead to situations that are difficult to resolve even with the use of the microscope and the information produced from a CBCT.
I have tried to broaden the discussion of just what innovation means and how the marketplace can distort what should be its true meaning. The world of endodontics can be made much safer than it presently is for both the instruments employed and the tooth (the patient) receiving the treatment, but to effectuate that goal, the lines of education must be much more open than they presently are.