Challenging Well-Marketed Endodontic Concepts and Gaining Insights

I started thinking about this post from the perspective of what I typically do compared to what is most extensively marketed as the most progressive endodontic techniques. First to be considered is canal instrumentation.

I predominantly shape and cleanse canals using 02 tapered stainless steel twisted reamers both unrelieved and relieved with a flat along their working lengths in a 30o handpiece oscillating at 3000-4000 cycles per minute. I do it this way for most of the canal preparation because it prevents instrument separation allowing me to apply them vigorously against all the canal walls cleansing even oval canals in three-dimensions and without distortion when applied to canals of increasing curvature. That is not the popular way things are done today.

Rather the emphasis is on rotary instrumentation using one or more NiTi instruments of varying tapers. As has been well documented in the literature, rotary introduces torsional and flexural stresses that can lead to instrument separation. As a consequence of their recognized vulnerability to separation, the instruments are used in a predominantly centered fashion inadequately cleansing oval canals in their larger diameter, again documented in the literature. The major manufacturers dismiss oscillation as old technology especially when coupled to stainless steel, a material that dominated in the past, but is now relegated as a thing of the past. While the major manufacturers of rotary NiTi dismiss oscillating stainless steel instrumentation, to date there is no adequate response to the fact that rotary carries with it the far greater possibility of instrument separation as well as the less recognized limitation of inadequate cleansing of oval canals.

Any comparison of the two should be based on clinical results, not some ill-defined suggestion that it is from a bygone era. That is not informative. It conjures an emotional response rather than one based on clinical evidence. I, as any endodontist, want 100% assurance that the instruments I employ to shape canals will remain intact and that they will not produce any apparent distortions. I achieve those goals with oscillating stainless steel reamers. The same cannot be said for rotary NiTi.

It is true that the 30o oscillating handpiece has been around for years. The same is true for stainless steel reamers. What did not exist was the implementation of relieved stainless steel twisted reamers in a 30o oscillating handpiece. Combining the preexisting 30o oscillating handpiece with the relieved twisted stainless steel reamers gives the dentist the means to shape canals in three dimensions without distortion virtually eliminating instrument separation. Engine-driven and implemented from the beginning, 30o oscillations has the potential to eliminate manual preparations and the time-consuming hand fatigue associated with it. Whatever wall the oscillating reamers are directed against will remove dentin coronally and as the instrument is withdrawn from the canal, the apical portion of the oscillating reamer works against the opposite wall from its most apical placement to the more coronal portion of the canal limited only by the extent of the withdrawal motion. In that way, three-dimensional cleansing is effected.

All the precautionary rules for the safe use of rotary NiTi, some of which compromise the integrity of the remaining tooth structure are not nearly as necessary when employing engine driven 30o oscillating reamers. There is a minimal need for straight-line access. Crown-down preparations are not necessary. The same stresses that are minimized in 30o oscillation also has a beneficial impact on the canal walls. A technique involving short 30o arcs of motion that prevents excessive torsional flexural stresses from impacting the oscillating instruments has the same benign impact on the canal walls. The vast body of research documenting the production of dentinal defects produced by rotary instruments is balanced by the impact of the canal walls on the rotating instruments.?

Those studies that say that rotary does not produce or expand preexisting dentinal defects are defining Newton’s Third Law as a one-way street. Yes, the canal walls can cause instrument separation, but the rotating instruments are incapable of causing defects in the canal walls. Newton’s Third Law of Motion states that two interactive bodies have an equal and opposite effect on each other. You can’t have one without the other.?

From the above discussion, I hope to convey my doubts about the beneficial impact of rotary NiTi instrumentation being the unquestioned advance in canal shaping and debridement that the major manufacturers marketed it as. In contrast, oscillating stainless steel relieved twisted reamers driven by a 30o?oscillating handpiece solves all the problems I encountered with rotary NiTi. I have been?making these mental comparisons every day for at least the last 30 years and cannot escape the observations that I have made here.

Thermoplastic obturation is another approach extensively marketed by the major manufacturers, a method of obturation that supposedly ensures a greater chance of a three-dimensional fill. To accomplish this stated goal, the manufacturers offer several different methods to achieve thermoplastic obturation. Carrier-based gutta percha points, far more expensive than conventional gutta perch points are warmed by an expensive heating oven that thermoplasticizes the gutta percha making it adapt to the canal walls as it is introduced into the canals. Another option is the use of heated spreaders and pluggers used for the same purpose of adapting the flowable gutta percha to a more intimate contact with the canal walls. Still another thermoplastic technique and the most expensive to date is the use of heating device that injects a flowable gutta percha into the canals directly and then is further compressed via a series of pluggers.

I have a different take on obturation generally employing a single well-fitted gutta percha point at least in the mesio-distal plane with all other spaces obdurated with a flowable epoxy resin cement that bonds to both the gutta percha and the canals walls. Unlike the thermoplastic techniques that are placed into the tooth at temperatures higher than the body’s, the materials are placed into the tooth at room temperature. The consequences of each are notable. Materials placed at room temperature will expand slightly as they warm to body temperature improving the seal. Those placed at temperatures higher than the body’s will contract as they cool to body temperature, a simple law of physics and create detectable gaps. It is also a fact that the room temperature epoxy resin cements are more flowable than the thermoplasticized gutta percha giving them a greater ability to adapt to all the nooks and crannies along the length the canals.

The epoxy resin cements, a derivative of AH26 has proven its value as an endodontic sealer over the past several decades. There is no mystery here or unexpected events. It is a polymer even more resistant to fluid degradation than gutta percha. Yet, if extruded over the apex it will be digested by the macrophage and no longer be seen on subsequent x-rays, a major advantage particularly if any is extruded into the IAN. The key to its safe application is the use of the bidirectional spiral, an applicator that is composed of coronal flutes that drive the cement apically while the three most apically situated flutes configured in the opposite plane drive the cement coronally. Used 3 mm short of the apex, this tool gives the dentist the ability to prevent extrusion of the cement when being applied and drives the cement laterally against all the canal walls as the apically directed and coronally directed flows of cement collide. Lateral movement of cement occurs along length as the bidirectional spiral applies the cement with a series of up and down strokes.

Finally, there has been a major marketing effort to establish the superiority of fiber composite posts over those of metal initially based on the similarity of the modulus of elasticity of both dentin and the fiber posts. From my perspective the argument supporting fiber posts is fallacious. The explanation for their superiority based on similar moduli of elasticity is that such materials will bend similarly under function. That, however, is not necessarily the case. To bend similarly, they must also have equal cross-sectional areas. The tooth, the recipient of the post, is far wider than the post being placed. As a consequence, the tooth is far less flexible than a post with a similar modulus of elasticity. A core supported by a post that is far more flexible than the tooth puts tremendous pressure on the margins of the overlying crown. The only way a fiber post has the rigidity to bend like the tooth it is in is if a considerable amount of coronal dentin is remaining to support the post in which case a post is not needed in the first place. It is ironic that fiber posts work best where they are not needed.

In comparison, a metal post with a much higher modulus of elasticity compensates for its thinner cross-sectional diameter compared to the tooth and bends far more like the tooth it is in. This interpretation takes into account all the facts that impact clinical usage and gives the dentist the information he/she needs to make well-informed decisions. We took these insights into account when we developed the split shank Flex-Post that allows a threaded post to act like a graduated tap giving the dentist a post with a combination of high retention, low insertional stresses and an even distribution of functional stresses, something no passive post whether made from metal or composite can duplicate.

These insights resulting from challenging dominant marketing concepts give the dentist a broader basis of comparison, one that is missing if we are limited to knowing only what the major marketing influences want us to know.

Regards, Barry