Evolution or revolution in endodontic thought

Dr. Eric Herbranson writes about embracing change and innovation with new technologies in cleaning, shaping, and packing.

Dr. Eric Herbranson discusses traditional theories and embracing change

As clinicians, we like to think of ourselves as scientists — or at least we think we base our opinions and practices on science and the scientific method. You know, that old process:

Make an observation. →  Ask a question. → Form a hypothesis. → Test your prediction. → Iterate your opinions. → “Truth”

Hopefully, this scientific process leads to some reliable version of the truth we can count on. But does it? What we are actually doing is forming a theory or mental model of how things work. We work off of these models, not off of a direct knowledge of how nature works. Our models are a couple of degrees of separation from the reality of nature — because of that, they are inherently not accurate.  The British statistician George F. P. Box quotes, “Remember that all models are wrong; the practical question is how wrong do they have to be to not be useful.”1 Or to put it more succinctly, “All models are wrong, but some are useful.”

We like our models. We hold many models of different sizes that form blocks of knowledge. These blocks can nest.  For instance, a big, overarching model is based on a number of smaller, more specific models. The cognitive psychologist John Sweller called these “schemas.”2 They are very useful in understanding how the brain works, understanding learning in communicating, in problem solving, etc. The acquisition and retentions of domain-specific knowledge in the form of schemas is what separates the expert from the novice. They form the “library” of information we use in our field. In any given scientific field, there will be agreed upon schemas with specific language prescribed to them.  For instance, in endodontics, we can have a schema labeled “obturation” that would include other schemas like “warm vertical condensation” and that could have “injected backfill” nested within it. And so it goes for the whole knowledge base of the field. There is a certain outline hierarchy to the information. This is the organization of the knowledge base we work off of professionally. This acquisition of knowledge, theories, models, schemas, or whatever you want to label them, takes effort and time. It represents a huge investment and is an asset with personal value. Nassim Taleb describes this in his book, The Black Swan:3

“The problem is that our ideas are sticky: once we produce a theory, we are not likely to change our minds — so those who delay developing their theories are better off. When you develop your opinions on the basis of weak evidence, you will have difficulty interpreting subsequent information that contradicts these opinions, even if this new information is obviously more accurate. Two mechanisms are at play here: the confirmation bias … and belief perseverance, the tendency not to reverse opinions you already have. Remember that we treat ideas like possessions, and it will be hard for us to part with them.”

My friend, John Khademi, in his article titled “Incommensurability in Endodontics,” characterized the resistance to change this way; “Knowledge blocks learning.”4 We’re comfortable with what we know; why change it! The problem is, to change our knowledge base requires more effort than acquiring it in the first place because we must deconstruct it before we can reconstruct it. Adult learning is more difficult than traditional education for this reason. There also may be an issue with less neuroplasticity with aging that makes change more difficult. Suffice to say, changing our knowledge base requires work and is resisted unless there is a compelling reason to put the effort in.

Figure 1: This is an SEM of a section of a canal system of an extracted root after the GW cycle was run. While the uninstrumented portion is rougher in appearance, it is as clean as the instrumented section

In reality, there is a constant slow change based on what Thomas Kuhn calls “normal science,”5 that is science, while based on questions and problem solving, tends to be evolutionary. The changes are small and serve to “polish” or refine the schemas. There is conceptual continuity with cumulative progress in this model. Our schemas adapt gracefully to this process because the changes are small and not disruptive. But Khun also describes necessary periods of revolutionary science where the discovery of “anomalies” in the base concepts results in new paradigms that lead to new questions and challenges the rules of the game.5 This disruptive process creates tension both in the individual as well as the whole field of endeavor. So rather than our schemas being setteled, they are disrupted, which creates echoes into other connected schemas. Having a conceptual change in a schema can affect the whole field.

We have an opportunity to put aside our biases, rebuild our schemas, reshuffle the treatment deck, and embrace a new way of doing a root canal.

Working through this process to where there is universal acceptance of the new information takes time. It can literally be decades. An example in endodontics would be the adoption of the surgical operating microscope. The initial push for adoption started in the early 1990s, driven to a significant degree by Dr. Gary Carr. There was much controversy and significant pushback by some established practitioners. Today it is a non-issue, and the assumption is endodontists will use a microscope for most of their work. One could rightly make the claim that the acceptance of surgical microscopes in endodontics was a 25- to 30-year process. Less obvious is how this adoption has changed other areas of the profession. The move toward smaller instruments, while driven by dentin conservation ideas, was made possible by the increased vision afforded by the microscopes. General adoption of CBCT technology has led to a significant awareness of tooth anatomy, which combined with improved vision, allows for more detailed and precise procedures.

Endodotics is based on the model described in “Endodontic triad for success” of shaping, cleaning, and packing.6 We believe that achieving success in these three areas will eliminate the pulpal remnants and bacteria that are judged to be the cause of apical periodontitis. Apical periodontitis is the endodontist’s disease. We believe that if we can eliminate organic debris through cleaning and shaping the canal to receive an obturation material that hermetically seals off the canal space, we will achieve endodontic “success.”7 This will allow the body to heal the disease of apical periodontitis. We have held this belief for so long and with such reverence that it is rarely challenged. The terms shaping, cleaning, and packing are labels for schemas that are packed with the science data, beliefs, protocols, and biases we use to support our model. They are cross-linked and form the conceptual framework of our general disease treatment theories. Through the years, there has been a lot of refining of these schemas and some divergence in viewpoint represented by various camps who promote and argue their particular biases. They also contain legacy ideas whose origins are foggy and validity suspect. But there is general agreement that the biological objectives of cleaned and sealed canals will result in healing of “our” disease. Of course, this is not “truth,” it is just a model of how we think nature works, so it is no doubt wrong in places. To some degree, it is also a house of cards with pockets of inconsistency and cognitive dissonance.

Technology really hasn’t impacted this. Microscopes and CBCT machines have improved our vision, and NiTi metalluragy have taken the stress out of shaping, but they have not fundamentally changed the concepts of how or why we do things. New technologies focused on debridement and disinfection will challenge the concepts of how and why we clean and shape.

One such new technology is the GentleWave® System (GW) (Sonendo®, Laguna Hills, California). The method of action of the device is considerably different than our legacy protocols, and this method of action disconnects instrumentation from disinfection. The GW uses a clever manipulation of fluid dynamic to create a multifrequency wall of small shock waves (multisonic sound) in the solutions while it replenishes the solutions. This sonic energy activates the chemical reactions of our traditional irrigation solutions of NaOCl and EDTA. The combination does the work to debride and disinfect the canal system. This energy travels to all aspects of the anatomy equally and is anatomy-agnostic in its effectiveness. It cleans distant small lateral anatomy as effectively as major anatomy. Its cleaning effectiveness is very good (can approach 100%) and significantly better than any of our legacy irrigation protocols.

Figure 2: This drawing is from an article arguing for the for aggressive shaping of the apex.8 This approach with its inherent compromise to tooth integrity is no longer needed with the advanced irrigation described here

The tendency is to view this technology as just a better mousetrap and plug that into the “cleaning” schema. That would be a mistake. The implications are more profound than that. There is an opportunity here to redefine our foundation treatment model.

The high degree of debridement of this technology creates the following opportunities.

      1. We no longer need to machine dentin to remove biofilm and debride pulp tissue. The sonic energy will do that work. This eliminates shaping as an adjunct to cleaning, which changes the function of the file. The result is a significant change in our protocols. In fact, in some situations, it may not be necessary to use a file at all. In a necrotic tooth with open anatomy the canal system can be effectively cleaned without using files. The resultant shape is what nature provided. But practically, files are needed in many cases. They are used to perform these tasks:
        1. Debulk the canal to reduce the debris load.
        2. Guarantee a path for the solutions.
        3. Smooth a rough canal to facilitate obturation if necessary.
        4. In most teeth, a single pass with one file carried to within a couple of mm of the apex will accomplish these objectives.
        5. Dentin conservation to maintain tooth strength is fully supported. There is no cleanliness advantage with larger shaping. Very small shapes can be cleaned as effectively as larger shapes.
      2. GW technology is capable of cleaning natural apical anatomy. This eliminates the need for apical shaping and recapitulation. It is no longer necessary to aggressively file an apex to clean it. In fact, it can be argued that any instrument placed at the apex is a disadvantage. The sonics will clean the apex without mechanical intervention.
      3. The need for very accurate length determination is significantly reduced. Electronic apex lengths and wire film radiographs are not generally necessary. Lengths judged from a CBCT scan are accurate enough for the debulking instrument pass. The technology will find and clean the apex to its natural end.
      4. A single visit is the desired model. The canal system is cleanest right after the device cycle is run, and obturation should proceed immediately if possible.
      5. Pre-op pain is minimized. Patients report very low levels of post-op pain, and most have complete relief within 24 hours regardless of their pre-op pain levels.
      6. The computer controlled closed-loop system creates consistent and predictable results.

Other technologies based on either the Er:YAG laser or the Er,Cr:YSGG laser are also challenging the way clinicians approach cleaning and shaping. The lasers have their own unique set of opportunities based on their individual methods of action. The lasers provide alternatives means for recapitulation, instrumentation, and disinfection.

Figure 3: This four-canaled lower molar illustrates the typical dentin-conserving shaping this new technology facilitates

An adjunct and complimentary technology change is the introduction of bioceramic sealers. Their ability to hermetically seal in large film thicknesses has changed obturation dynamics.  Instead of the gutta percha being the main obturation material, the sealer is. The gutta-percha point becomes the condensation device for the sealer. A single cone bioceramic fill with some minimal hydraulics can provide complete three-dimensional obturation to the thinner, rougher shapes that result from this technology. So the “look” will change. The fat smooth shapes of the past will be replaced with skinnier and less smooth fills. This will be the new look and our new definition of beauty.

In conclusion, while evaluating this new technology for effectiveness and efficiency, we need to take a broad view of how it impacts all our protocols to get the maximum benefit.  That view will show us we are facing a revolutionary change in how we approach the Endodontic Triad. We have an opportunity to put aside our biases, rebuild our schemas, reshuffle the treatment deck, and embrace a new way of doing a root canal. The opportunity is greater than we think.

Dr. John West discusses some colleagues’ perceptions of cleaning, shaping, and packing in relation to endodontic predictability in his article, “The Endodontic Triad: dead or alive?” at https://endopracticeus.com/the-endodontic-triad-dead-or-alive/

Eric Herbranson, DDS, MS, received his DDS and MS in Endodontics from Loma Linda University. He is recently retired from active practice in the San Francisco Bay area. He has a long history of lecturing nationally and internationally.


Disclosure: Dr. Herbranson is a member of the Sonendo® Scientific Advisory Board.

  1. Box George FP. All models are wrong. https://en.wikipedia.org/wiki/George_E._P._Box. Accessed August 1. 2022.
  2. Sweller, J. Cognitive load during problem solving: Effects on learning, Cognitive Science, 1988;12, 257-285
  3. Taleb NN. The Black Swan: The Impact of the Highly Improbable. Random House; 1997.
  4. Khademi J, Clark D. Incommensurability in Endodontics: The Role of the Endodontic Triad. N J Dent Assoc. 2016;87(4):18-20.
  5. Kuhn TS. The Structure of Scientific Revolution. 3rd ed. The University of Chicago Press; 1966.
  6. Ruddle CJ. Endodontic triad for success: The role of minimally invasive technology. Dent Today. 2015;34(5):76-80.
  7. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am. 1974;18(2): 269-296.
  8. Card SJ, Sigurdsson A, Orstavik D, Trope M. The effectiveness of increased apical enlargement in reducing intracanal bacteria. J Endo. 2002;28(11)779-783.

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