For the past 40 years, the general focus of Endodontics has been on the mechanics of cleaning and shaping canal systems. First we accepted the concept of " the canal system" vs. the root canal (mid 1960s) and the relationship of lesions of endodontic origin to portals of exit (1970s-80s). Advances in metallurgy allowed for the use of rotary motion rather than push-pull filing techniques and an increase in the efficiency of instrumentation (1990s-2000). While these changes were taking place, far less emphasis was being placed on canal filling techniques. The technique of warm vertical compaction of gutta percha had a major influence on many clinicians and it spawned a whole generation of advocates and teachers who were influenced by Schilder's Boston Technique. However, until relatively recently, you could still find clinicians who used silver cones to fill canals. Cold lateral techniques were also still in the majority because warm vertical techniques were thought to be too "technique sensitive". This is changing. Warm vertical techniques, as advocated by Buchanan and Ruddle are gaining in popularity and it is difficult to find any modern dentists who use silver cones (or Sargenti paste) for endodontic treatment anymore. Warm vertical techniques are now routinely taught in Dental Schools.
At the same time, the radiographic "look" of the canal has also changed. In the early "silver cone" years of the specialty (before a true appreciation of canal anatomy had arrived) emphasis was placed on culturing canals as well as trying to machine canals (by hand) to a specific size and then placing a correspondingly sized silver cone into that machined space. In some cases it worked well. In many cases it didn't, not so much because of the lack of ability of the silver cone to seal the canal but more because most of the canals were grossly under-prepared, inadequately cleaned and contaminated. As canal preparation techniques evolved in the late 1960s, it became increasingly clear that the concept of "making the canal fit the filling material" was completely the opposite of what was necessary to fill these complex systems. We needed filling materials that could be adapted to the nuances of the canal system anatomy and we needed shapes that would allow us to do this.
The first attempts to laterally "deform" gutta percha into this space were based upon an idea that sequential space could be created and gutta percha cones stuffed into the canal space as a spreader made room for it. This is "Lateral Condensation". Sealers of various compositions filled the space that was not occupied by gutta percha. We had the classic " Cold Gutta Percha cones frozen in a sea of sealer". Just how many accessory gutta percha cones could be placed in that MB2 canal of the upper molar with poor access? It all depended on how much of an effort you wanted to expend! Research began to show that the best of these laterally "condensed" cases worked because as the spreaders were worked laterally AND vertically, it was the vertical component that caused the apical adaptation, such as it was. Again, these cases were often shaped less than optimally because the concept of the continuously tapering preparation had not taken hold. This shape was best exemplified by Ingle's Washington Monument comparison.
The warm gutta percha technique (as taught by Schilder) became the gold standard in the 1970s. Greater appreciation of the canal as a system necessitated an obturation technique that molded itself to the canal shape. In order to do this, the limitations of the instruments available at the time (stainless and carbon steel files) demanded that shapes be larger to allow them to negotiate to the terminus and to allow for placement of vertical condensers to within 4-7 mms of the apex. Sealers were used but only because they were necessary to compensate for the cooling of the gutta percha after it was compacted. Initially, many clinicians (and Endodontists!) thought the shapes were "overenlarged". They were said to contribute to fractures due to thin dentin walls and the pressures of vertical condensation. Yet, Endodontics also began to appreciate that uncleaned, unfilled anatomy DID matter and that this was the best way to achieve success. Properly performed Warm gutta percha technique continues to be used successfully in millions of cases per year, with excellent rates of success.
Once it was recognized that plasticized, warm gutta percha was the optimal technique, research began to find different ways to make it moldable to the canal space. In the 1990s, the development of Ni-Ti rotary instruments allowed for two things: (1) Greater efficiency and less ledging by using reaming motions in a crown down method and (2) Better negotiation of curved canals due to the flexibility of the Ni-Ti metal. The goals of canal preparation were performed without having to enlarge the coronal aspects as much as we had in the past. "Fatter" canals got "skinnier" with the use of Ni-Tis.
The Thermafill technique was introduced in an attempt to bridge the "silver cone - gutta percha void". It involved the heating of gutta percha on a "carrier" system, first made of metal and then later on - in plastic. When used correctly it was also very successful but it had several drawbacks:
(1) Undepreparation of the canal space could cause "stripping" of the gutta percha from the carrier as it was forcefully placed in the canal. The result - basically a single cone- metal or plastic carrier obturation in the apical portion - not the desired result. So like Warm vertical compaction, this too was "technique dependent".
(2) Retreatment of these cases required removal of the carrier prior to re-cleaning and repacking of the canal.
(3) Surgical treatment of these cases was more difficult than normal due to complications caused by metal carriers.
The incorporation of "standardized" tapered preparation techniques also allowed for greater standardization of the gutta percha points that were used in vertical compaction techniques, such as Buchanan's "System B". .04 .06 and .08 tapered cones more closely approximated the shapes created by the Ni-Ti instrumentation. I used them (and still do for many cases) but I had some reservations about how much plasticity of the gutta percha was actually occurring in the apical few mms. The narrower, more slender shapes created by these instruments failed to take into consideration one important fact: Gutta Percha is a fairly good insulator and because of this apical deformation during heated condensation requires "bulk". It is MUCH easier to "move" gutta percha in a larger canal than in a smaller one. As I began to use these cones, I occasionally would accidentally pull one out during condensation. When I checked them closely, I found that the apical section was still dead cold. In these "skinner" canals, I was getting no heat down there at all and that concerned me greatly.
Finding Alternatives: The System S Technique
In October of 2002, I visited the office of Dr. John Stropko in Scottsdale Az. Dr. Stropko (also a Boston U. graduate) agreed that the lack of deformation of gutta percha points at the apical third was a problem. For the past 12 years, he has overcome this by using a pure Obtura (Heated Gutta Percha Gun) based technique that he calls the System S technique. It is a .06 taper-based technique that stresses proper canal shape prior to obturation. He uses minimal sealer and application of gutta percha to the canal space is entirely by the Obtura, followed immediately by application of vertical pressures with a Schilder or Dovgan plugger. Dr. Stropko is quick to point out that optimal results can only be achieved by using Schwed "NORMAL SET gutta percha" pellets (NOT LOW temperature formulations!) with Obtura machine set at maximum temperature. For most clinicians, the immediate reaction is: How can you achieve apical control of the material? Doesn't it come flying out of the apex? The answer lies in the canal preparation - keeping the apex as small as is practical (He suggests a Tulsa Profile 29 size #4 instrument - equivalent to a 0.21 file). By applying vertical forces to the prewarmed gutta percha you get tremendous lateral and vertical hydraulics inside the apical parts of the canal and great reproduction of anatomy. Be forewarned, Dr. Stropko is not afraid of very slight, minimal overextensions of the filling material that occur as multiple portals of exit are filled. Therefore, it may not be a good technique in parts of the world where anything (sealer or gutta percha) placed in the periapex is considered unacceptable. I have used this technique since Oct. of '02 and I have been amazed at the results and at the level of control. You can find more information about Dr. Stropko and his courses at: http://www.excelinendo.com/
Although gutta percha has been the standard material for almost 100 years, many in research feel that its days in endodontics are numbered. As Endodontic success rates continue to increase, research has begun to focus on coronal seal and to the endodontic-restorative continuum. Many endodontists are currently placing bonded flowable composites over canal orifices to improve the seal prior to restoration and decrease the likelihood of long-term coronal leakage. The next step in the evolution of endodontic filling materials is to provide a "gutta percha-like" material that actually bonds to the dentin of the canal walls.
Fibrefill (Pentron) - The Fiberfill system consists of an adhesive bonding agent, a light-curable CaOH based resin sealer and a fiber post with an apical terminus of gutta percha. The Fiberfill obturator is a resin and glass fiber post with a terminal gutta percha tip. The gutta percha is available either in 5 or 8mm lengths. The diameter of the post is available in sizes 30, 40, 50, 60, 70 and 80. Unfortunately, while the apical gutta percha is retreatable, removal of the bonded fiber post has proven to be difficult. There has also been some suggestion that the use of this resin-based system can actually increase the strength of roots, something that has never been possible with any other post system. I have not used this system and I am reluctant to do so because of the potential difficulty of trying to remove the bonded obturator during retreatment.
Resilon (Trade name "Epiphany"- Manufactured By Pentron ) - This is the most promising material for replacement of Gutta Percha. The Epiphany obturation system has been shown to resist leakage significantly better (six times better) than gutta percha based obturation, while strengthening the root by more than 20%. The centerpiece of this system is a soft resin obturating material called Resilon. Resilon is a bondable material made from polymers of polyester. Its unique formula contains fillers and radiopacifiers in a soft resin matrix. Resilon looks like gutta percha in your hand and on a radiograph. It handles like gutta percha and can be thermoplasticized at lower temperatures. It is biocompatible and retrievable, like gutta percha. The Epiphany obturation material (points or pellets made with Resilon), combined with the Epiphany dual cured resin sealer and the Epiphany primer, bind together in the canal to create a "monoblock". This results in roots that are strengthened and a coronal seal as part of the canal filling process. The Epiphany Obturation System can be used with your present root canal filling technique by substituting the Epiphany materials for your gutta percha and your sealant. Resilon will be released in the very near future. I am awaiting a sample of this material for my own clinical tests. It looks very promising.
(Sources: An Evaluation of microbial leakage in roots filled with a thermoplastic synthetic polymer based root canal filling material (Resilon) or with gutta percha - Shipper, Ostravik, Teixeira and Trope - Recently submitted to the Journal of Endodontics for publication) and Fracture Resistance of Endodontically treated Roots using a new type of resin filling material - Teixeira, Teixeira, Thompson and Trope - Recently submitted to the Journal of the American Dental Association.)