I was perusing through the 11th edition of Cohen’s Pathways of the Pulp, the latest edition that came out this past October. I was particularly interested in the book’s assessment of pulpal anatomy, how its removal was most effectively addressed and the impact of instrumentation on the integrity of the remaining tooth structure. What I wanted to see was whether or not the latest edition, a book used by many dental schools as the basis for the students’ endodontic education was reflecting the research of recent years that has documented the production of dentinal micro-cracks induced by greater tapered rotary shaping that lead to an increased incidence of vertical root fracture. I also wanted to see if the lack of cleansing in the bucco-lingual dimension resulting from the conical shaping greater tapered rotary NiTi instrumentation creates was being addressed.
Chapter 6, Cleaning and Shaping the Root Canal System discuss a host of instrumentation systems. With the exception of the Self-adjusting file (SAF) all systems impose a conically tapered shape regardless of the original anatomy leaving untouched buccal and lingual extensions of oval canals and the isthmuses that join them. The author noted that “in vitro data for this system (SAF) suggest that indeed more wall contract is made compared to rotary files, resulting in better debridement and antimicrobial efficacy.” This result is in stark contrast to all other rotary systems. Essentially, the SAF system uniformly enlarges the original anatomy cleansing the canals in both the mesio-distal and bucco-lingual planes removing more tissue while minimizing the amount of dentin removed to accomplish this basic goal. It should be noted that minimal coverage was given to this system while the details of use were given to a host of other approaches.
What is missing in this discussion is the realization that the SAF can more effectively instrument highly oval canals because the hollow tubed construction allows it to be compressed to adapt to a variety of odd shapes. In other words, its compressibility provides them the ability to become as small as the space they are entering into, expanding to the point where the sandpaper like walls of the hollow mesh rub lightly against the walls. Used with a 0.4 mm vertical amplitude of motion oscillating at 5000 cycles per minute, the SAF literally sands the walls of the canal in three dimensions doing away with conical shaping that sacrifices too much tooth structure in the mesio-distal plane in the hopes of gaining adequate contact in the bucco-lingual plane, a goal that is not achieved when highly oval isthmus-like anatomy is present.
The insight that should be staring us in the face is that an instrument narrower than the space within which it is present can effectively instrument a canal by purposely working it vigorously against any and all walls. As long as the amplitude of motion is short, 30º-45º the dentist need not worry about instrument separation. Oscillating at 3000-4000 cycles per minute, shaping and cleansing in both the mesio-distal and bucco-lingual planes is accomplished rapidly and effectively. By recognizing this ability, it does away with the notion of the need for conical shaping that in turn produce dentinal micro-cracks, excessive thinning of the root in the mesio-distal plane and produces conditions for an increased incidence of vertical root fractures. While the SAF has not proven to be commercially viable for other reasons, it amply demonstrates the superior ability to cleanse canals when instruments can adapt to smaller isthmus-like anatomy. Thin 02 tapered stainless steel relieved reamers are actually thinner in cross-section than the SAF. As a result they can enter narrower spaces even more effectively than the SAF preparing the canals uniformly with a minimal reduction of dentin and a maximum removal of pulpal tissue.
This book imo misses this essential point. It loads us up with facts, but does little to help us think critically about the issues that still plaque “modern” endodontics.
Chapter 21 discusses cracks and fractures, mainly from a diagnostic point of view. It is only toward the end of the chapter that etiology is brought up. It is cited that “the most common dental procedure contributing to vertical root fracture is endodontic treatment.” Excessive root canal preparations as well as the production of micro-cracks caused by rotary instrumentation are causative factors. From my perspective cracks and fractures should be correlated closely to the chapter on instrumentation. There is no question that the action of greater tapered rotary files whether used in a continuously rotating fashion or an interrupted fashion are inducing stresses that lead to dentinal defects and vertical root fractures. Yet, these harmful effects are not correlated. By separating the injurious impact of instrumentation from the mechanics of instrumentation, the book does not act as an efficient guide for caution and a pathway to safer and more effective endodontics.
I have talked in the past about the increasing corporate influence in the educational process. In my view this extends to the educational books that are employed. A culture strongly influenced by corporatism will seek as its end goal the growing sales of its products. To accomplish that goal, a seamless approach must be presented to the student bodies comprising the exclusive adoption of the endodontic instrumentation system produced by the manufacturer that has “partnered” with the university, lectures given that reinforce the choices the administration made as well as the source material. Any book that presents material in such a way that leads to critical thinking introduces unpredictable events that can undermine the seamless environment that is conducive to passive acceptance. Such a book would be unacceptable to a university that is committed to an academic/industrial relationship and would be self-defeating for an author whose own personal goal is the use of his book as a standard. In short, a book used by the students must comport with administrative goals that have already been molded by a binding corporate relationship.
The best alternative is a level of independence provided the student body that allows them to seek outside sources of information, forming study clubs that address the void created by the implementation of a single system, an increased reliance on a wide range of research and its implications, often data that does not support what is being taught. This approach implies the administrative approval and encouragement of critical thinking and is likely to be resisted by those institutions that have already made commitments to their corporate brethren. When the universities give the corporations exclusive access to the student body, at a minimum it should be limited to the actual academic program. That it extends to policies that prohibit the formation of independent study clubs is an insult to the students and demeaning to any university administration that would impose such restrictions. Corporations should be limited in what they can expect from cooperative universities. That these limitations have not been imposed appears to make the universities desperate for corporate funding. From a negotiating point of view, if the universities did impose these limitations on corporate influence, the corporations would still compete for access to the student bodies despite their loss of total control. They seek out advantage wherever they can find it and must be met with an effective counterforce. This is both academically and morally the correct position for the universities to take imo. The alternative is ever increasing corporate influence allowing them to create markets for products that only have to pass the test of salesmanship rather than the more drawn out and often obscured process of critical review that multiple research studies offer over time. The former leads to blinded consumerism, the latter to an educated professional.