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
|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
IN PURSUIT OF THE TRUE MONOBLOC
A NEW MONOBLOC MATERIAL AND TECHNIQUE
|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.
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.)|
|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 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.
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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.