Validation by the Major Manufacturers
I WAS READING some comments about the use of single NiTi instruments employed in a reciprocating handpiece to shape canals. This is the latest iteration of NiTi after twenty years of selling dentists on a plethora of rotary systems that must be used with great caution to prevent separations and canal distortions. Using reciprocation will now significantly reduce the incidence of breakage, something we have been talking about the last ten years. I suppose one could say that the introduction of NiTi used in reciprocation validates what we have been saying all this time. That is true, but it also confirms far more than that. If one looks at the NiTi instruments now being used in reciprocation, one will note that they are reamers, not files, regardless of what they are called. For more than twenty years, we have espoused the use of reamers, based on their obvious benefits, saying specifically that K-files and the method in which they are used are both wrong and counterproductive for effective canal shaping.
The major manufacturers are now validating the safety that derives from reciprocation versus rotation and the effectiveness of reamers as opposed to K-files (Figure 1). However, we believe that they still fall short in selling a system that relies on a single instrument for total shaping. In highly calcified and tortuous canals, using an initial instrument with a tip size of 25 and a taper of 06 is asking for debris impaction, blockage, and the potential for canal distortion. It makes so much more sense to accomplish initial negotiation to length using far thinner reamers that engage so much less along length. Common sense tells us that less engagement along length produces superior tactile perception of what the tip of the instrument is engaging, something that is critical when differentiating between encountering a solid wall versus a tight canal. Yes, there are canals that would allow the initial use of a 25/06 instrument, but one doesn’t know that they will allow it until after the fact, and in those cases where the 25/06 should not have been used the integrity and patency of the canals may have been needlessly compromised.
On the other side of instrumentation, a 25/06 will produce shaping that is inadequate to remove the debris present, particularly in oval canals. Nor, according to the literature, will it leave a space that is wide enough for adequate irrigation. Having validated the use of reciprocation, elimination of K-files, and the adoption of reamers, the major manufaturers are coming ever closer to the type of system we have advocated for years. They differ from us in what we consider inadequate instrumentation, both at the initial stages and at the end stages. They simply prepare a space that can be filled with a radiopaque white line to the apex, a goal that was proven inadequate by Dr. Herb Schilder more than forty years ago. Furthermore, they employ unrelieved reamers that have no capacity to differentiate between a round canal and an oval one, limiting the dentist’s ability to make correct decisions on the degree of shaping that should be done. For example, if we know that a relieved 25 reamer has some resistance in one orientation, but increased resistance when rotated 90 degrees, the instruments confirm the fact that the canal is oval in cross section and requires shaping to the walls of the major diameter, something a symmetric instrument would have no ability to discern. When shaping canals with NiTi, whether used in rotation or reciprocation, the “snapback” (Figure 2) of NiTi, a property that always makes the metal seek a straight orientation, is another incentive to limit the size of the preparation, since the degree of selective shaping to the outside wall of curved canals increases in direct relationship to the tip size and taper of the NiTi instrument used and the degree of canal curvature that must be traversed. Stainless steel relieved reamers, while not as flexible as comparably-sized NiTi instruments, have the ability to record curvatures and are not plagued by “snapback,” making them highly adaptable to the tortuous pathways of the canals they may encounter.
Relieved reamers (Figure 3) have enhanced abilities over non-relieved reamers. They are more flexible, engage less along length, and have two vertical columns of chisels (where the relieved flat cuts across the flutes) that cut in both the clockwise and counterclockwise directions. Used in sequence from thinner to thicker, they maximize tactile perception, telling the dentist when the instrument must be removed and bent at the tip to negotiate around an impediment. A single instrument far larger both in tip size and taper than an initial reamer with an 06 tip and an 02 taper will engage far more along length, severely limiting the dentist’s ability to know what the tip of the instrument is engaging. This over-engagement represents counterproductive engineering and is not a product of common sense.
Given the history of rotary NiTi, prospering even though the instruments introduced separation anxiety as a reality that must be constantly dealt with, and then successfully selling the single-use concept that turned rotary NiTi’s weakness into a financial success, the manufacturers may also be able to successfully introduce an instrument that offers minimal tactile perception while shaping canals to a dimension that the research clearly states is inadequate. Doing so would, in my opinion, be a marketing success for the manufacturers, not a success for either the doctors doing the work or the patients receiving such treatment.
The viewpoints expressed here run contrary to what will be marketed as the latest paradigm improvement in all the endodontic ages. What is crucially needed is an open forum that correlates the ideal goals of instrumentation with a critical analysis of the design and utilization of instruments that are introduced to achieve those goals. We must determine whether these instruments function in a way that delivers on the ideal goals or runs counterproductive to them. Commercialization should not come in until the end, since the goal of marketing a product is simply to maximize sales regardless of the product’s benefits. With enough marketing money behind a product, it will be sold like a rigged beauty contest in which whatever traits the most heavily marketed contestant has will be viewed as the best that exist. If you doubt that and you use rotary NiTi, think about the acceptance of the single-use concept that so dramatically increased our costs while still not eliminating the breakage we all sought to avoid. Please refer to the attached radiographs for some clinical cases that highlight the results gained by using relieved reamers in a reciprocating handpiece (Figures 4–7).
January - March 2011