Separating What’s Real From What Is Claimed To Be Real In Endodontic Instrumentation: Part Two

What is claimed: The conventional wisdom is that the use of plastic 3D printed teeth prepares the students for their clinical experience while making any judgments on their individual performances much easier given the fact that each student is working on identical tooth models. That is false.

As previously stated, plastic 3D printed teeth are fabricated from materials that are 1/2 to 1/3 the hardness of dentin. Consequently, the tactile perception the students encounter is significantly different from what they will experience clinically. In terms of rotary NiTi, a system the vast majority of dental students are being exposed to, the softer material offers less resistance in negotiating to the apex, requiring fewer rotations to reach it reducing the torsional stresses and cyclic fatigue these instruments will encounter in the preparation of the canals resulting in a lower incidence of instrument separation. This would be all well and good if the ultimate goal was to work on plastic teeth. That, obviously, is not the case. The tactile perception these students familiarize themselves with via this preclinical training increases their vulnerability to instrument separation when they apply the techniques they learned on plastic teeth to natural teeth that unfortunately are now in live human beings.

So, a conflict exists. The students are being trained on plastic teeth that do not simulate the resistance encountered in natural teeth. To further aggravate the situation, they are all being uniformly trained given the identical models each student is trained on. Given these conditions makes for easier appraisal by the faculty, but what is the point if the tactile perceptions they are developing do not simulate what they will encounter clinically?

. What is claimed: The schools are fulfilling their primary goal of developing the students’ critical thinking skills. That is false.

The requirements for the initiation of critical thinking is to first be exposed to the entire range of data that is associated with any topic under discussion. In the case of endodontic instrumentation, it would include the goals of canal debridement in the safest most effective and efficient manner. The safest manner relates to the integrity of the instruments being employed as well as their minimal impact on the structural integrity of the tooth. The most effective manner relates to the degree of proficiency in removing the pulpal tissue and any bacteria present within the confines of the canals and the dentinal tubules embedded within those walls. The most efficient manner relates to the speed with which the instrumentation process can be accomplished without compromising on safety and effectiveness. A basic approach to critical thinking as it applies to endodontic instrumentation would be to consider the impact of the instruments’ form and function on these three goals.

There is no evidence that the determination of what system is taught to the student bodies is based on the exercise of critical thinking. Rather, the technique the students learn is based on which sponsoring corporation is most generous in their financial offerings to the schools. The decision is handed down from the top, rather than a process of analysis that would evolve from an approach based on critical thinking. This represents a hierarchical authoritarian approach that has nothing in common with critical thinking. Case in point: Schools in most cases teach the initial use of stainless steel K-files to create the glide path that will subsequently be followed by one rotary NiTi system or another. A common problem associated with stainless steel K-files is their tendency to impact debris apically with loss of length. The reason is obvious from the perspective of form and function. The K-files have about 30 flutes along their working length of 16 mm so compacted that the flutes are predominantly horizontally oriented.

An instrument so constructed will shave dentin away on the pull stroke, but also impact any debris present in the canal apically when the in stroke is applied. This is not a rare event. It can be greatly reduced or entirely avoided by substituting stainless steel relieved reamers for those K-files. The predominantly vertical flute orientation of the reamers shave dentin away when the horizontal rotary motion is applied. It does not shave away dentin on the pull stroke like the K-file. On the in stroke the vertically oriented flutes of the relieved reamer are poorly designed to impact debris apically unlike the K-file. This is not rocket science. Even a mild attempt at critical thinking quickly makes it apparent that the reamer design is more efficient while being far less likely to produce apical impactions of debris. What goes for understanding why relieved stainless steel reamers are a better choice for the initial shaping of canals compared to K-files could be applied to the problems associated with the shortcomings of rotary NiTi. Illuminating those shortcomings and the alternatives available to overcome those shortcomings is not in the interest of the sponsoring corporations or the universities that accept such sponsorships. Consequently, the process of critical thinking and the insights it would lead to is never initiated and actively prohibited.

What is claimed: It is impossible to develop critical thinking skills unless the students are exposed to a broad unbiased range of information that does not exist in the commercialized environment that is the norm in too many dental schools. That is true.

Regarding the evolution of rotary NiTi instrumentation, heat treated NiTi has become increasingly flexible making it more resistant to cyclic fatigue. As it becomes more resistant to cyclic fatigue, it becomes more vulnerable to torsional failure. To date no treatment of NiTi has resulted in an improvement in resistance to both torsional stresses and cyclic fatigue and separated instruments remain the major shortcoming in their usage that in turn compromises their main function of debriding canals three-dimensionally.

The periapical x-ray gives us clear evidence that the canals have been cleansed three-dimensionally. That is false.

To date the only method that tells us whether or not we have cleansed the canals three-dimensionally is the micro-ct scan, something that cannot be applied clinically. What it tells us on extracted teeth is that the rotary systems do a poor job in three-dimensional debridement when oval and flat pulpal anatomy is present. Extrapolating from that data, it becomes obvious that the mesio-distal image we have on a periapical x-ray gives us no information regarding the bucco-lingual preparation of the canal, the plane that has been shown to be inadequately debrided using the micro-ct scan on extracted teeth. This evidence is ignored by rotary advocates stating that the tissue in the bucco-lingual extensions is removed by various high-powered irrigation systems, systems associated with the development of dentinal micro-cracks and periapical trauma. The assessment of rotary advocates is to accept these high-priced irrigation systems to compensate for the shortcomings despite the undesirable unintended consequences they are associated with. It is not a conclusion resulting from an analysis of all available data. It is the selective use of data to support systems for commercial reasons rather than an analysis of their strengths and weaknesses.

While anyone has the right to disagree with me about particulars, I don’t see how one can be against the concept of critical thinking, a process that requires the broadest spectrum of data available. Critical thinking is so vital to rational discussion that even those who have commercial interests would never come out saying it is not the basis of progress even as they deny its application. As long as the dominant incentive of corporate profits remain the goal, something encouraged by the adoption of that incentive by universities, critical thinking simply cannot exist and the effort to rationalize its avoidance demeans all those involved in the process.

Regards, Barry