A New Endodontic Obturation Technique

The ultimate goal of endodontic obturation has remained the same for the past 50 years: a true hermetic seal. A seal where there is no leakage coronally, apically, or laterally. A seal that will help ensure endodontic success and thereby maintain root canal therapy as a preferred treatment modality. An additional goal has been to create a technique so user-friendly that it will result in the greatest majority of dentists performing the best possible obturation.
This article will review the evolution of endodontic obturation and introduce a new obturation technique using improved glass ionomer technology.

THE EVOLUTION OF OBTURATION

Endodontic obturation has witnessed a true evolution. Previously, we had silver point techniques that attempted to match the silver points to a preparation. This was basically not a bad idea, it’s just that we had the wrong preparation and materials. Nonetheless, silver points were popular until the late 1960s, when room temperature lateral condensation of gutta-percha replaced silver points.
Lateral condensation is a technique still taught in dental schools, and it can deliver good results when performed properly. However, in the mid 1980s, thermoplastic techniques began to replace lateral condensation. One of the advantages of a thermoplastic technique is that when performed properly, it creates a homogeneous mass of gutta-percha. Previous techniques such as lateral condensation often created voids because of a mismatch between spreaders and accessory cones. The result frequently was a series of cones placed in a sea of cement. Consequently, many in the endodontic community viewed heated gutta-percha techniques as a “step up” in terms of methodology. Unfortunately, what was missed in the excitement about a homogeneous fill was that heated gutta-percha shrinks significantly when cooled.
In actuality, what creates the seal in all of these techniques (silver points, lateral condensation, thermoplastic methods) is the sealer. The sealer is what seals the canal; gutta- percha merely takes up space, and if heated, can hopefully move sealer into webs and fins.
Figure 1. A hermetic seal can be created if there is a monobloc between the canal wall, the sealer, and the master cone. Precision in endodontics contributes to achieving this goal.

Therefore, as we have progressed in endodontic obturation, we have come to realize that the sealer is the key to obtaining a true hermetic seal. The challenge, more specifically, has been to find a sealer that would simultaneously bond to the canal wall as well as to the gutta-percha cone or a similar core material. Endodontic science has realized that if it could satisfy such a challenge, we would then have the possibility of creating a true monobloc (Figure 1).

Virtually everyone in endodontics agrees that a true monobloc will result in a hermetic seal. The real challenge has been to develop a true monobloc technique that will work in all teeth (straight canals and curved canals) and in the greatest majority of clinicians’ hands. As the challenge of developing a monobloc has been researched, the endodontic cements that have received the most attention have been resins and glass ionomers. In particular, we have always viewed the ultimate obturation technique as being a true single cone method that would deliver a monobloc obturation. This would allow the greatest percentage of clinicians to deliver the highest quality obturation results. However, before we go further in this discussion, we need to review the material properties of resin and glass ionomer used in endodontics.

RESIN AND GLASS IONOMER CEMENTS IN ENDODONTICS

Glass ionomer cements, which are in actuality glass polyalkenoate cements, have had widespread use in medicine.1 Their use particularly in orthopedic surgery is a result of their biocompatibility. According to De Bruyne and De Moor,2 “These cements generate no heat while setting and consequently will not harm any tissue. Because these cements have the ability to bind to bone and do not undergo any appreciable shrinkage while setting, their principal use in orthopedics has been the stabilization of implanted devices and bony fragments and the reconstruction or obliteration of bony defects.”
Although the endodontic application of glass ionomer was initially investigated by Pitt Ford3 in 1979, it was not until the mid 1980s and early 1990s that a number of endodontists and scientists seriously re-searched glass ionomer as an endodontic sealer. Although the most popular glass ionomer sealer at the time displayed tremendous potential, its use as a sealer still had some limitations. The early generation of glass ionomer sealers came in premeasured capsules that unfortunately were placed in amalgamators (instead of a proper mixing unit). Consequently, the mixing left something to be desired, and the result was that the consistency of the sealer was erratic and the working time of the cement was reduced. Subsequently, these early glass ionomer endodontic cements were viewed as having too short a working time, which echoed Pitt Ford’s findings in 1979. In actuality, this was very unfair to these cements.
Another problem with these early generations of glass ionomer and resin sealers in endodontics was that neither method was able to develop a true monobloc. Although there were advocates on both sides of the argument, research showed that both the glass ionomer and resin sealers each had some advantages and some limitations. However, one thing that both the resin and glass ionomer advocates could agree on was that obturation was headed in the direction of sealer-based techniques rather than the mechanical packing and melting of gutta-percha.
It is very interesting to see how the two materials differed. The resins were shown to have a good seal between the sealer and the gutta-percha cone, but their seal to the canal wall was questionable. The glass ionomer cements, on the other hand, displayed a good seal to the canal wall, but their seal to the gutta-percha was questionable. So, as the 20th century came to a close, we still found ourselves searching for a technique that could consistently deliver a true monobloc obturation.

IN PURSUIT OF THE TRUE MONOBLOC

In the pursuit of a true monobloc single cone technique, we have felt allegiance to glass ionomer because of its superior biocompatibility and its physical properties. But more specifically, what is it that we really like about glass ionomers?
Glass ionomers not only do well in moist environments (wet bonding), they actually create an ionic bond to the dentin. This bond is critical if we are thinking in terms of a monobloc and an eventual hermetic seal. Glass ionomer sealers are also nonresorbable, which is critical in any monocone or sealer-based obturation technique. The fact that glass ionomers do not undergo resorption is not a problem because of their great biocompatibility. In fact, as previously mentioned, these cements are used routinely in orthopedic surgery to hold fixtures or fragments in place. Furthermore, Friedman and others demonstrated that glass ionomer did not undergo resorption when extruded periapically, thereby confirming its low tissue solubility.4
Glass ionomer is also considered to be bioactive, in the sense that it can be stimulated to release fluoride. Fluoride can be important in endodontics because it will act as an antibacterial agent and has been shown to promote remineralization. Glass ionomer cements react well in areas of inflammation.
Another aspect of glass ionomer that is preferred (when compared to resins) is that it responds well in the presence of sodium hypochlorite. Resins and their bonding capability are adversely affected by exposure to bleach (sodium hypochlorite). This is not a factor in restorative dentistry, but becomes problematic in endodontics, where we routinely use copious amounts of bleach during a root canal procedure. Webs, fins, and anastomoses are difficult, at best, to dry completely. Glass ionomer is hydrophilic and will bond to dentin in the presence of moisture.
Setting time is also important in obturation, and the setting time of glass ionomer is such that the clinician can do a post preparation and placement at the same visit as the endodontic procedure. This is very convenient for today’s clinician.
Resins, although excellent materials in restorative dentistry, have, in our opinion, some further limitations in their use as endodontic sealers. The fact that the majority of resin sealers are primer dependent makes it difficult, and questionable, that the primer will be adequately delivered around many canal curvatures. Also, the fact that resin sealers can undergo resorption places an additional limitation on their use in a true single cone technique. Many clinicians are also concerned about extruding resin sealers past the apex because of sensitivity problems. The toxicity of resin material is such that if extruded past the apex, it is considered to be more of a concern than glass ionomer.
While the merits and properties of glass ionomer were well known, there still were some limitations with the first-generation glass ionomer sealers.5 The handling characteristics of these sealers were a challenge, and they did not produce a sufficient working time for most practitioners. Additionally, they did not display a bond to gutta-percha, which was necessary to qualify as a true monobloc technique. Therefore, altering the properties of glass ionomer sealer to meet the requirements of a monobloc was our first challenge.

A NEW MONOBLOC MATERIAL AND TECHNIQUE

This article introduces a new obturation technique that utilizes improved glass ionomer technology…the ActiV GP Precision Obturation System (Brasseler). In fact, this system takes technology to the nanoparticle level. In a sense, materials science is coming of age in endodontics.
In developing this system, the first change we had to make to conventional glass ionomer sealers was with the working time. A working time of 3 to 4 minutes is simply unrealistic for endodontic purposes. We needed at least 10 minutes. Furthermore, we had to change the cement so that it could be modified (if desired) and would be user-friendly for the dental staff. By modifying its particle sizes, we have been able to significantly extend the working time. The working time of ActiV GP sealer is 12 minutes on a paper pad and easily 20 minutes on a chilled glass slab. Furthermore, ActiV GP sealer comes in a powder/liquid combination that allows the assistant to mix it to a consistency that is favorable for the doctor and the individual case. Additionally, cleanup is very easy, as all that is required is to run the glass slab and spatula under warm water.
Figure 2. X-ray showing the superior radiopacity of ActiV GP in a single monobloc obturation. This case demonstrates the synchronicity achieved between EndoSequence files and the ActiV GP master cone.

In addition to improving the handling characteristics and extending the working time, we have increased the radiopacity of this glass ionomer sealer. We now have a radiopacity with ActiV GP sealer of 9.2 on a scale of 1 to 10. Previously, ZOE-based sealers were in the range of 6.7, and the epoxy resins were the greatest at 9.1. It really doesn’t matter if it is 9.1 or 9.2 or even 8.8. The key point is that the radiopacity is excellent. Clinicians certainly want to perform their endodontic cases well, but they also want their cases to look good. This is important to all practitioners (Figure 2).
Although the initial changes made were with the sealer, the challenge remained of lack of a bond between the sealer and the gutta-percha. We like gutta-percha and its properties, so there had to be a way to create a bond between the ActiV GP sealer and the gutta-percha. This was critical if we were going to get a true monobloc fill, thereby creating a hermetic seal.

Figure 3. SEM demonstrating the bond between the glass ionomer coating (arrows) and the gutta-percha cone. The thickness of the adhesion coating is 2 µm. (SEM by Dr. Quanzu Yang.) Figure 4. Upon manual bending of the coated cones up to 180º, there was no delamination of the glass ionomer coating from the gutta-percha. The bending method confirms the excellent adhesion and flexibility of the glass ionomer coating. (SEM by Dr. Quanzu Yang.)

Reticulating the gutta- percha was an option, but the better alternative proved to be glass ionomer itself. Glass ionomer particles that are present in the sealer are incorporated into the gutta- percha cones at a percentage that does not affect the properties of gutta-percha. One further change was made to the glass ionomer-impregnated cones. The cones were coated with glass ionomer particles at a thickness of 2 µm. The science (SEM) shows that there is no gap between the coating of glass ionomer and the glass ionomer-impregnated gutta-percha cones (Figure 3). The excellence of this glass ionomer adhesion is such that the cones can be bent up to 180º without showing any signs or symptoms of delamination. This is very significant in short radius, curved canals (Figure 4).

Figure 5. SEM demonstrating the bond between the glass ionomer sealer and the glass ionomer-coated gutta- percha cone. Glass ionomer particles are visible within the gutta-percha cone. (SEM by Dr. Quanzu Yang.)
Figure 6. Light refractive metallograph at 100x demonstrating the relationship between the dentin, ActiV GP sealer, and the master cone; a good example of the monobloc obturation that is possible with the ActiV GP System. Note that this is a true sagittal image, not a pie section. Verification of a true monobloc obturation technique. Figure 7. Very high magnification image (500x) of the bond that is created with ActiV GP. Notice the glass ionomer particles that are present in the gutta-percha.

As a result of the glass ionomer coating that has been placed on the glass ionomer-impregnated gutta- percha cones, ActiV GP sealer bonds directly to the ActiV GP points (Figure 5). This is very significant, as the challenge with glass ionomer sealers has always been the bond to a gutta-percha cone. Taking particles from the sealer itself and placing them into the gutta-percha cones, and then coating the cones with a thin layer of glass ionomer particles (2 µm), has allowed the development of a true monobloc between the canal wall, the ActiV GP sealer, and the master cone. The monobloc facilitates the creation of a hermetic seal, which is a milestone in endodontics (Figures 6 and 7).

Figure 8. ActiV GP Precision Obturation System.

Figure 9. ActiV GP Plus cones come with a handle and depth markings to expedite insertion into the canal.

The regular ActiV GP System includes gutta-percha points that are manufactured in a traditional design, with the further enhancement of being impregnated and coated with glass ionomer. The other choice, ActiV GP Plus, has a different cone design. It employs calibration rings for easy depth measurement and a convenient handle that facilitates easy insertion into the canal (Figures 8 and 9).

Figure 10. Leakage study demonstrating the sealing characteristics of the ActiV GP System. ActiV GP sealer is seen going into the fins of this tooth. A total lack of leakage is seen alongside the primary cone and sealer. Also, there appears to be no leakage underneath the glass ionomer canal cap that was placed on top of the ob-turated canal. The tooth was im-mersed in India ink for 10 days. Leak-age study by Drs. Koch and Brave.
Figures 11a and 11b. Leakage study confirming the ability of the ActiV GP sealer to enter and seal apical deltas (a, b). Notice the complete lack of leakage alongside the main canals. The tooth was immersed in India ink for 10 days. Leakage study by Drs. Koch and Brave.

The ActiV GP system, for the first time in endodontics, delivers a monobloc obturation result with a true monocone technique. However, the system is precision based. As mentioned in previous articles, precision-based endodontics requires accuracy between the file and the master cone.6 All ActiV GP points are laser verified to match the preparations made by the 0.04 or 0.06 tapered EndoSequence file system (Brasseler). The precision matching of the primary cone to the preparation is very important with any single cone technique because the accuracy of the cones to the preparation minimizes the amount of sealer and any potential shrinkage. It has been shown repeatedly that the thicker the layer of sealer, the more prone it may be to dimensional change (shrinkage). Although shrinkage can occur with all sealers, glass ionomer has a minimal amount of material change. Consequently, it may be stated that a true single cone technique should be accomplished with a constant tapered preparation such as a 0.04 or 0.06.7 Additionally, the hydraulics achieved by a constant taper 0.04 or 0.06 preparation will drive sealer into the webs and fins (Figures 10, 11a, and 11b). A variable taper technique is not recommended because of the lack of precision and the increasing amount of sealer as one progresses coronally in the canal. This lack of precision and synchronicity is why most variable taper preparations are associated with thermoplastic techniques.

CLINICAL EXAMPLES

Figure 12. Anterior case completed through existing crown and bridge.

Figure 13. Central incisor that displays the conservative nature of synchronized endodontics.

In the following cases, we can see the benefits of a constant taper preparation that is synchronized to an obturation technique. In the first case, which is a very common one, the challenge is going through the crown and bridge in a manner that will not break the porcelain or destroy a significant portion of the tooth underneath the crown. This is always a concern in these cases because when one makes access through a crown, you are always at the mercy of the laboratory technician who stacked the glass. As is evidenced by the final x-ray, the preparation was made and the case completed with a minimum of tooth structure removal (Figure 12). A second anterior case further demonstrates the precision (and conservation of tooth structure) that all dentists can achieve when performing synchronized root canal therapy (Figure 13).

Figure 14. Maxillary premolar with a clean, precise post preparation in the palatal canal. Figure 15. The contrast in radiopacity between a eugenol-based sealer (No. 30) and ActiV GP (No. 31). (Image courtesy of Dr. Bradley Trattner.)
ActiV GP is not intended for use as a thermoplastic technique (the heat will quickly set the cement), but it certainly lends itself well to a burnout technique used for a post. The example shown in Figure 14 demonstrates how a Touch ‘n Heat (SybronEndo) was used effectively to place a post prep in the lingual canal. The glass ionomer cement burns out fast, clean, and in a predictable manner.
The following molar case, completed by an endodontist (Dr. Bradley Trattner), demonstrates the superb radiopacity of ActiV GP. The first molar was obturated using EndoSequence gutta-percha and Roth’s 801 cement. The second molar was filled by the ActiV GP method. The contrast in radiopacity is shown by the digital image (Figure 15).
In another case, Dr. Trattner has again performed an excellent service for his patient. The slender canals present in tooth No. 30 are a good indication for the ActiV GP technique, and it is obvious that straight line access was also a key to obtaining this result (Figure 16).
Figure 16. Slender canals in mandibular molars can be obturated successfully with a monocone technique utilizing glass ionomer technology (ActiV GP). (Image courtesy of Dr. Bradley Trattner.) Figure 17. Mandibular molar demonstrating the excellent flow characteristics of a modified glass ionomer sealer. (Image courtesy of Dr. Ali Nasseh.)

Everyone likes to see endodontic cases from Boston, and Dr. Ali Nasseh has contributed the following. The first case is beautifully shaped, and the “puff” on the distal canal is evidence of the flow characteristics of the ActiV GP Sealer (Figure 17). Additionally, a canal cap of glass ionomer has been placed on top of all the canals. This is a wise idea. In fact, some dental schools in North America are recommending that the dentist should cover the entire chamber floor with glass ionomer to prevent leakage. This is the clinician’s choice, but it is highly recommended to at least place a final canal cap on top of the obturated canal.8 If retreatment is ever necessary, the caps are easily removed with an ultrasonic device. Yet, if the patient loses the temporary filling, they have not lost the root canal.

Figures 18a and 18b. A good example of how a separated instrument (a) may be incorporated into the final fill. No-tice the multiple portals of exit that have been filled with the ActiV GP sealer (b). (Image courtesy of Dr. Ali Nasseh.)

The second case contributed by Dr. Nasseh melds the concepts of instrument design and materials science. The preoperative image shows a separated Sequence file in the mesial root of a lower molar. Because the Sequence file is actually a true reamer, Dr. Nasseh was able to readily bypass the segment. After instrumentation and shaping was completed, ActiV GP was used to entomb the segment and fill the entire root canal system. In addition to the entombed segment, evidence is shown of multiple portals of exit being filled by the glass ionomer sealer (Figures 18a and 18b).

In the past, some have questioned the ability to retreat glass ionomer when used in a root canal. This is because they were working with canals that had been entirely filled with glass ionomer. In actuality, they were using glass ionomer as a filler, not a sealer. The consistent accuracy of ActiV GP points (laser verified) results in an extremely close match between the preparation and the master cone. Therefore, only a minimal layer of sealer is required, with the net result being a canal that is principally filled with gutta-percha material. Consequently, retreatment is readily achieved with the ActiV GP system.

 

CONCLUSION

In this article, a true monocone obturation technique (ActiV GP) has been introduced that demonstrates the capacity to create a hermetic seal within the root canal system. This is achieved through a monobloc established between the canal wall, the sealer, and an enhanced cone. When combined with a constant taper preparation, the simplicity of ActiV GP enables the greatest majority of practitioners to produce exceptional obturation results.


References

1. McLean JW, Nicholson JW, Wilson AD. Proposed nomenclature for glass-ionomer dental cements and related materials. Quintessence Int. 1994;25:587-589.

2. De Bruyne MA, De Moor RJ. The use of glass ionomer cements in both conventional and surgical endodontics. Int Endod J. 2004;37:91-104.

3. Pitt Ford TR. The leakage of root fillings using glass ionomer cement and other materials. Br Dent J. 1979;146:273-278.

4. Friedman S, Lost C, Zarrabian M, et al. Evaluation of success and failure after endodontic therapy using a glass ionomer cement sealer. J Endod. 1995;21:384-390.

5. Koch K, Min PS, Stewart GG. Comparison of apical leakage between Ketac Endo sealer and Grossman sealer. Oral Surg Oral Med Oral Pathol. 1994;78:784-787.

6. Koch K, Brave D. Endodontic synchronicity. Compend Contin Educ Dent. 2005;26:218-224.

7. Koch K, Brave D. Introducing the ActiV GP precision obturation system. Dental Equipment & Materials. Jan 2006. Available at: http://de.pennnet.com/Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=249400&VERSION_NUM=3&p=55. Accessed March 21, 2006.

8. Mavec JC, McClanahan SB, Minah GE, et al. Effects of an intracanal glass ionomer barrier on coronal microleakage in teeth with post space. J Endod. 2006;32:120-122.


Dr. Koch is the founder and past director of the program in postdoctoral endodontics at the Harvard School of Dental Medicine. In addition to maintaining a private practice limited to endodontics, he has written numerous articles on endodontics and maintains a faculty position at Harvard. Dr. Koch is a co-founder of Real World Endo and can be reached by visiting realworldendo.com.

Dr. Brave is a diplomate of the American Board of Endodontics and is a member of the College of Dip-lomates. In endodontic practice for more than 25 years, he has lectured extensively throughout North America and holds several patents, including the VisiFrame. Formerly an associate clinical professor at the University of Pennsylvania, Dr. Brave currently holds a staff position at The Johns Hopkins Hospital. He is a co-founder of Real World Endo and can be reached by visiting realworldendo.com.

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