The Pacific Endodontic Research Foundation (PERF) was created in 1991 as a public, non-profit research foundation with the expressed goal of performing endodontic research. This research was an outgrowth of work on fresh human cadaver dissections I had helped Terry Tanaka with at his Clinical Research. I had noticed in doing the dissections that some of the specimens had had apical surgery performed at some point in the past.
Most of these prior surgeries presented with endodontic pathosis around them. I asked Terry if I could study these cases in detail after the dissections were complete and he was kind enough to consent—and in fact, encouraged me to do so. At around this time, a paper was published by Frank and Weine looking at long-term follow-up of clinical cases in their practices and which showed a disturbing finding: the long-term success of endodontic surgery appeared to be around 50%.
This paper intrigued me and I thought perhaps these cadaver cases could tell us why the failure rate was so high.To perform this work, I needed not only histological analysis of the cases, but electron microscope analysis. Commercial electron microscope analysis is expensive and early experience utilizing a commercial imaging service proved to be inordinately expensive and this research was being funded personally by my endodontic income. Since I had several hundred specimens to examine and also had some electronics background (as an electronic technician in the Navy and as a Ham radio operator WB2BBJ), I elected to purchase a used scanning electron microscope at a government surplus auction. I installed the electron microscope in our garage.
The results of the study uncovered some very unexpected findings. The Frank and Weine paper held out the theory that it was the amalgam retro filling material and its subsequent breakdown that was responsible for the failures. Our work cast significant doubt on that conclusion. What we found was that there were four main errors committed in classical endodontic surgery and many of these surgeries had all four errors present. Error #1: Failure to address the anatomical complexity present at the apex due to lack of proper visibility. From our work, it was clear a magnification of at least 6X was required, and sometimes more.This had the dramatic consequence of requiring a microscopic approach to endodontic surgery. At the time, no endodontist was using an operating microscope in endodontics.
Error #2: The classical retroprepation of small, round, fillings bears no relationship to the actual canal configuration present and that a small, round, retro fill is seldom, if ever, desired. Our work showed that these classical small, round, fillings are probably leaking from the day they are placed.
Error #3: The retropreparation itself is poorly placed and is almost never placed down the long axis of the tooth, but instead placed obliquely into the root. Such placement makes a hermetic seal problematical at best and extremely unlikely in most cases.
Error #4: The exaggerated bevel required to perform a retropreparation is a large problem, in and of itself. The long bevels typically placed during endodontic surgery have the effect of elongating the required retroprep in a B-L direction, greatly increasing the circumference needing to be sealed.Many of the cases showed that because of this elongated bevel, the lingual part of the root was never actually cut through.
After discovering these 4 main errors, we conducted research that attempted to address each of these errors in turn. Since we used an operating microscope in our research, it was not a huge jump to bring the microscope into the endodontic office. We were not the first to use a microscope in a clinical setting. Howard Selden was the first endodontist to use a microscope as a clinical tool. But this microscope was poorly configured, had only one power, was ergonomically difficult to use, and never gained acceptance in any area of dentistry and the manufacturer stopped making them after the initial lot didn’t sell.
Our microscope, a variation of our research microscope, was ergonomically easier to use, had 5 different magnifications, had an assistants viewing port, and 35mm and video capabilities. It rapidly became the standard configuration in endodontics and today represent a 20 miliion dollars industry in dentistry.
The second major development was our development of ultrasonic root end preparation. This device revolutionized surgical endodontics by replacing the retro-prepping hand piece and round bur with an ultrasonic tool that enabled a retro preparation up the longitudinal axis of the root. Indeed, if it wasn’t for ultrasonic root preparation technique, the microscope may never have gained wide acceptance in endodontics. Clinicians almost universally were hostile to the idea of microscopic endodontics but they all were VERY interested in ultrasonic surgical techniques. Fortunately the ultrasonic technique was intimately entwined with a microscopic approach and the use of tiny retro preparation mirrors which were also developed at PERF.
Endodontic advances resulting directly from PERF Research
- Widespread adoption of a microscopic approach in endodontics
- Abandonment of classical round-bur retropreparation technique and replacement by ultrasonic preparation technique
- Ability to resect roots perpendicular to their longitudinal axis.
- Development of microsurgical soft tissue protocols (atraumatic flap management) resulting in rapid healing.