Second Opinion: What Exactly is Modern Endodontics? by Dr. Scott T. Weed

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by Dr. Scott T. Weed

Second opinions are common in health care, whether a doctor is sorting out a difficult case or a patient is not sure what to do next. In the context of our magazine, the first opinion will always belong to the reader. This feature will allow fellow dental professionals to share their opinions on various topics, providing you with a “second opinion.” Perhaps some of these observations will change your mind, while others will solidify your position. In the end, our goal is to create discussion and debate to enrich our profession. – Thomas Giacobbi, DDS, FAGD, Editorial Director, Dentaltown Magazine

A key review paper was published in 2007 by a team at the Eastman Dental Institute in London, UK.1 Their work was of tremendous magnitude and attempted to pool the vast array of outcomes studied in primary endodontic therapy from the previous 40 years. Part of their conclusion states: “The reported success rates have failed to improve over the last four or five decades.”

How could anyone say our success rates haven’t improved?

Because they probably haven’t. The reason we’re not improving in our overall success rates is because we focus too much on the things that matter the least. This is going to require a little explaining on my part, so bear with me as I take a slightly circuitous course to a place I call “modern endodontics.”

The Foundation: Science

The reality is we don’t completely understand endodontic disease, nor do we fully understand how our endodontic treatments affect teeth long term (for good and for bad). Is it possible that some of the things we do clinically to “fix” teeth might harm them over time? Don’t we have literature to guide us—clinical science?

The purpose of science is to explain and predict. It’s like drawing a map. Listening to the messages in endodontics today, it’s clear that many of our teachers have mistaken the “map” for the “terrain.” That is, they think the way they understand things is the way things actually are. The 20th century physicist E.T. Jaynes describes this as the Mind Projection Fallacy. The map will never be the terrain and any inconsistencies between the two are always the map’s fault!

At a recent endodontic meeting here in the U.S., a well-known educator was asked, “What is the explanation for [the high success rates of ] the millions of maxillary first molars that have never had an MB2 canal uncovered or instrumented?”2 The answer: “I don’t know and I don’t care.” Apparently explanation and prediction take a back seat when you think you’ve got things figured out!

Specifically, you and I are interested in clinical research/science. We were all taught certain principles of endodontics in dental school and these were presented as doctrine. Straight-line access. X number of file sizes beyond the first file to bind. Minimum apical file size. All canals visible at the same time with one eye closed. (This could be a long list if we all got together and reminisced.)

You would think we had rock solid literature to back up all these recommendations. I’ve come to the conclusion that where it counts, we are severely lacking in our science. The purpose of clinical research is to inform the decision-making process. Each of us is confronted with challenging clinical situations every day and we need to know what to do.

In briefly discussing science in this section, my purpose was to highlight some of the uncertainty in what we do. Understanding uncertainty helps us better define and understand modern endodontics.

Modern Endodontics: What It’s Not

Taking the exclusionary approach, let’s talk about what modern endodontics is not. Here are a few questions:

Is modern endodontics about the latest and greatest secret sauce for irrigation? How about sealers? New rotary files? What about lasers? Ultrasonics? Reciprocation? Cone-beam CT?

I want the silver bullet just as much as the next clinician, but if the research from the Eastman Institute is to be believed, it doesn’t seem to work like that. My argument is that we’re too focused on the small issues that can’t possibly have large effects on outcomes. Why do we focus on these kinds of issues? Because they are “study-able.” It’s easier to compare leakage of sealers in vitro than to conduct long-term randomized clinical trials.

So in a word, “no.” Modern endodontics is not found in the things mentioned above. There isn’t some special sealer that will eliminate root canal failures. There isn’t an irrigation device, sonic/ultrasonic/laser/etc., that will “clean away” failure. That’s because there’s a bigger gorilla in the room.

The same authors at the Eastman Institute released several studies after the one I mentioned before, all on outcomes of endodontic therapy. In their 2010 paper,3 the authors identified four factors affecting failure of endodontically treated teeth: how the tooth is restored, presence of adjacent teeth, involvement in a prosthesis and tooth type (molar versus non molar). Which of these has anything to do with the actual endodontics?

First Things First

Renowned author and motivational speaker Dr. Stephen R. Covey talked about “First Things First,” habit number three, in his popular self-help book, The Seven Habits of Highly Effective People.4 An example of this principle in regard to population health is instructive. What would be a more worthwhile endeavor: finding a cure for ebola virus or implementing the basic hygienic practices of hand washing and quarantining of sick individuals? (There have only been 1,630 known cases of Zaire Ebola Virus Disease in the past 38 years since the disease was described.)5

Does it really matter which brand file you use if the case is going to sit for weeks in a stinky cotton pellet and Cavit?

We need to start defining those strategies that make the biggest difference to the patient. The old, outdated approach to endodontics is all about legacy systems and taking pride in what we think we know (recall, “I don’t know and I don’t care”). Modern endodontics embraces uncertainty and weighs risks and benefits accordingly. It is built on sophisticated decisionmaking, excellence in execution and careful application of available tools.

Decision Making

When I graduated from dental school, I seriously embraced the idea that you find the canal or perforate the root trying to find it. What a stupid philosophy. Sometimes our decision- making skills only improve as we discard old ideas that impede progress.

One of these ideas is that we must do everything clinically based on some kind of scientific study. There’s a problem with this. An exhaustive review of the literature on sodium hypochlorite does nothing to inform our decisions in a clear way. Should we use full strength? Half strength? Buffered? The literature offers us no such help in this simple matter. The same could be said for most of the clinical decisions we make in endodontics.

This statement will draw criticism from many, and if you feel yourself wanting to argue with this, consider that most measures of outcomes in our science aren’t actual outcomes that affect patients. A bacterial count in a canal says nothing about how long the tooth lasts in the patient’s mouth.

In the absence of clear scientific guidance, I strongly feel our treatments should err on the side of conservation of tooth. Teeth need to be drilled on as much as my chest bone needs to be cracked open. Don’t do it. But if you must, be delicate and careful. Conservative treatment is often more difficult to pull off than reckless treatment.

The concept of minimal invasion of the tooth is taking hold, not because it’s got rock solid scientific backing, but because it just makes sense. I don’t need a scientific study to tell me that drilling on the tooth won’t make it stronger.

We need to put ourselves in the shoes of our patients: What do they care about? It’s pretty simple, really. They want to keep their teeth and balance that with the time, cost and aggravation of making that happen. If it’s the tooth we’re trying to save with endodontics, why are we drilling so much of it? Weak teeth don’t go the distance.

Excellence in Execution

How do I personally execute minimally invasive endodontics with excellence? The first thing is magnification and illumination. I not only use a microscope, but I also have my chairside assistant in the scope with me via a co-observation tube. She’s managing the field in an aggressive way so I can see.

Second, I’ve abandoned the old tools and concepts that resulted in unnecessary dentin removal. Straight-line access (SLA) has nothing to do with the long axis of the tooth and everything to do with the location and angulation of canal orifices. I strongly question the old dogma—“legacy concepts”—specific to canal preparation. Do I really need to open the canal orifice larger than 1.0mm?

Third, excellence means knowing limits. I thoroughly discuss the limitations of my skills with each patient. My practice is built on excellence and I can’t afford marginal results. It also means that I aggressively follow up my cases. It’s easy to ignorantly think that everything we do “works” and that we have little failure. If you aren’t seeing your own failing cases, someone else is.

Careful Application of Available Tools

If the essence of modern endodontics is preservation of tooth structure, we must discard those tools that get in the way of this goal. If you saw my Townie Meeting presentation from 2013, you know how I feel about round burs for endodontic access. They are awkward, destructive and prone to errors that needlessly sacrifice dentin. Long, slender diamonds are much more appropriate.

We need the tools to be conservative—smaller tools. There are so many engine-driven nickel-titanium files on the market yet they all do the same thing: they cut shapes in roots. Whether they rotate or reciprocate or oscillate, it doesn’t matter. I’m looking for a file that cuts less. The feature of the file most directly governing how much a file cuts is the maximum flute diameter. If a manufacturer came to me and said, “What can I make for you?” I’d reply, “Make me a file with less diameter at the shank.” The only reason to open the canal over 1.0mm at the orifice is convenience. Why weaken the tooth for convenience?

Smaller tools also include thin ultrasonic tips and tiny rotary burs with sufficient length to do work in the pulp chamber. Obviously, this assumes you can see what you’re doing (back to the magnification discussion).

3D imaging can be a tremendous benefit in elucidating tricky anatomy. It can be helpful with diagnoses as well. I feel very strongly about the competency one must possess to own and operate this technology. Unfortunately, there are few resources in dentistry to help us gain the expertise necessary to maximize the benefits of this technology to our patients. Thankfully, medicine has much deeper and broader experience in this realm.

Bringing it All Together

As a specialist, I often get questions from colleagues about specific materials and techniques. I think it’s our formal schooling process that drives us toward laundry lists and cook books and to make crib sheets.

I rarely have brand-specific recommendations unless it’s something I feel makes a big difference in being conservative. For example, there are only so many files on the market today with a maximum flute diameter equal to or less than 1mm. I can’t, in good conscience, recommend files larger than that. It has nothing to do with their metallurgy, flute design, etc. It’s simply a size issue.

As long as the clinician sticks to the tried-and-true material for endodontic treatments, applies conservative access and shaping approaches along with careful technique, success rates will be quite high. This means that all canals should be located and instrumented, irrigated, obturated, and an immediate permanent core should be placed. Until I see other evidence, these steps seem to predictably get cases to heal (although they are not always necessary given the many “exceptions” to the rules we all see in our practices).


Modern endodontics isn’t about simply swapping out old for new product iterations while keeping the outdated mentality of treatment. Modern endodontics is in the conservation of dentin; it is in the skills required to practice minimally invasive dentistry; and it is in the careful implementation in the proper tools.

The teeth harmed the least tend to last the longest. I encourage each one of us to examine our work carefully and see if it might not be possible to drill a little less dentin next time we perform endodontic therapy.

  1. “Outcome of primary root canal treatment: systematic review of the literature - part 1. Effects of study characteristics on probability of success.” Ng YL, Mann V, Rahbaran S, Lewsey J, Gulabivala K. Int Endod J. 2007 Dec;40(12):921-39.
  2. Kulild and Peters showed 95% of these teeth to have 2 MB canals! “Incidence and configuration of canal systems in the mesiobuccal root of maxillary first and second molars.” Kulild JC1, Peters DD. J Endod. 1990 Jul;16(7):311-7.
  3. Int Endod J. 2010 Mar;43(3):171-89. “Tooth survival following non-surgical root canal treatment: a systematic review of the literature.” Ng YL1, Mann V, Gulabivala K.
  4. Covey, S. R. (1989). The 7 Habits of Highly Effective People . 1989, NY: Free Press.
  5. J Gen Virol May 2014 vir.0.067199-0

  Author's Bio
Dr. Scott Weed received his DDS from the University of the Pacific in San Francisco, California. Upon graduation from dental school, Dr. Weed was commissioned a lieutenant in the Navy and completed an Advanced Education in General Dentistry at the United States Naval Dental Center, Okinawa, Japan. He then practiced general dentistry for two years with his father, Dr. Robert F. Weed, in Fallon, Nevada. Dr. Weed left general practice and then completed a two-year specialty program in endodontics at the University of Southern California in Los Angeles, California. It was in Los Angeles that Dr. Weed conceived of the Reno Endodontic Continuum.


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