Simple, Precise, and Predictable Root Canal Obturation

In a previous article (Dentistry Today, March 2002) titled “Another Look at Root Canal Obturation,” we acknowledged that the “right way” to obturate a canal remains elusive, and that even after 100 years we are still searching. As is often the case, the “right way” doesn’t have to be complicated. We have found that when it comes to obturation the principle of “keep it simple and safe” is a valid one.

The principles of three-dimensional obturation are quite simple, the most basic one being the simplest of all: obturation can only be as good as the preparation. No matter what technique is used, how perfectly shaped the canal, or how skilled the operator, if the canal is not well cleaned it cannot be well obturated. It’s the same as saying a beautiful crown placed on a poor preparation without retention can’t be a good crown.

In our article we also stated that obturation and instrumentation are so closely related that there would be a severe lack of continuity to discuss one without the other. For this reason, we begin with a brief discussion on how instrumentation relates to obturation.

INSTRUMENTATION AND OBTURATION: ONE NEEDS THE OTHER

A three-dimensional obturation first starts with cleaning in three dimensions. To achieve a three-dimensional obturation, due importance must be given to canal diameter and not just canal length. By itself, a perfect length will not give us a three-dimensional cleaning, thereby making a three-dimensional obturation unobtainable. How are we so sure? Because we would reject any suggestion that instrumenting a canal to a size 10 or 15 master apical file would be acceptable. But, if a size 10 or 15 is too small, what is the correct size? This is a critical question that must be addressed.

In this age of advanced technology and a mandate for science in endodontics, we need more information about apical canal sizes and how they can be determined clinically. Apical canal cleaning and shaping is the most important aspect of instrumentation. Canal diameter cannot remain the “forgotten dimension” in endodontics. (We gave our views and the science to support them in an article published in Dentistry Today, May 2001.)

The answer to the correct apical preparation size is deceptively simple. The correct apical preparation size is dictated by the size of the canal being instrumented. There is no such thing as standard canal sizes, and besides that, canal sizes change throughout life. Three-dimensional cleaning removes debris in the canal and on the canal walls. Removing debris from the apical walls of curved canals requires instrument sizes large enough to touch all walls at the same time (at any given location). Rotary instruments that are too small can’t accomplish this, and circumferentially filing to clean all walls in the critical apical region is an endodontic myth that should have been discarded long ago.

Does three-dimensional cleaning mean we must instrument all lateral canals, isthmuses, cul-de-sacs, and apical deltas? Of course, that would be nice, but it’s really physically impossible because of the complexity of root canal anatomy. We cannot mechanically clean lateral canals. We cannot mechanically clean the narrow isthmuses between main canals, and we cannot mechanically clean the very narrow branches of apical deltas.

Neither should we expect an irrigating solution such as sodium hydrochloride to clean these areas by dissolving out the debris. Even with generous coronal and mid-root flaring and copious irrigation, research shows that these areas cannot be predictably cleaned with current irrigation techniques. Remember, we are dealing with very small spaces. There are three reasons why we should not expect irrigation to completely solve the problem: (1) there is a very small volume of solution present in these areas; (2) there is a very small area of contact between the irrigant and tissue/debris to be cleaned; and (3) there is a limited exchange of solution because of the confined space and because the bubbles formed by the action of sodium hydrochloride act as a barrier against the entry of fresh irrigant.

Although we are unable to achieve a “perfect” cleaning every time with instruments and irrigants, we have to do our best. So, what can we do? We can strive to clean the main canal by instrumenting to both the correct length and diameter. This will remove almost all of the noxious elements—the “critical mass,” so to speak. After cleaning as best we can, we then obturate in three dimensions to protect the canal and periradicular tissues from future microbial invasion from the mouth.

The importance of a three-dimensional obturation becomes clear when we consider what it will do. It will (1) isolate the areas that cannot be cleaned (isthmuses, fins, and cul-de-sacs) and (2) block the main canal side of lateral canals and apical deltas, thereby preventing any reinforcements from entering these areas. The noxious elements within the lateral canals and apical deltas are open to the highly vascular periradicular tissues. Just as it occurs elsewhere, the defenses of the body’s immune system invade the areas where the noxious elements are trapped, destroying the microorganisms and resorbing the necrotic tissue.

INSTRUMENTATION AND TECHNIQUE

To properly clean and prepare the root canal system for obturation, we use LightSpeed instruments and the SimpliFill obturation system. The SimpliFill obturation system was designed to be compatible with the LightSpeed Instrumentation System used for cleaning and shaping the canal, therefore we do not recommend using SimpliFill with any other instrumentation system. Rather than taking a “one size fits all” approach, we believe each and every root canal is different, and its cleaning and shaping should be customized according to its unique anatomy. This isn’t difficult. Although the size and shape of each canal is customized, the technique is the same for all teeth regardless of canal size, length, and shape. It just so happens that by taking this approach, canals are typically prepared to larger sizes, as appropriate, resulting in cleaner canals that are easier to obturate.

Figure 1. The LightSpeed root canal instrument. Its short blade and flexible shaft provide flexibility and accurate tactile feedback.

LightSpeed instruments have a very short blade and a small diameter noncutting shaft (Figure 1). Shortening the blade and eliminating the taper gives the instrument flexibility and accurate tactile feedback. The dentist can feel when optimal mechanical cleaning is realized. When effective irrigation is added and three-dimensional chemo-mechanical cleaning has been achieved, you can now turn your attention to three-dimensional obturation.

THE SIMPLIFILL OBTURATION SYSTEM

The SimpliFill system was designed to meet the following goals: (1) must not leave a metal or plastic carrier in the canal that makes post space or re-treatment difficult; (2) must be a simple technique; (3) must not require special equipment and may be used with a low initial cost; (4) must not require heat; no possibility of gutta-percha shrinkage upon cooling; (5) must not require over-enlarging the canal coronally, thus weakening the tooth needlessly;  (6) must reduce the time and number of instruments used to clean and shape the canal; and (7) must seal canals as well as, or preferably better than, other common obturation techniques.

The results of two published studies1,2 using the SimpliFill system are shown in Tables 1 and 2.

Materials

Figure 2. The SimpliFill Carrier with 5-mm Apical GP Plug attached. Choose a Plug whose size matches the final apical instrument used during instrumentation.

Figure 2 shows the SimpliFill Carrier and Apical GP Plug. The Plug is a precisely sized solid piece of gutta-percha 5 mm in length with a 0.02 mm taper. The Plug obturates the apical 5 mm of the canal and, if a post is needed, the technique provides space for a post while also ensuring an apical seal. The Carrier for the Apical GP Plug is made from stainless steel. It is flexible enough to negotiate curves and rigid enough to push the tight-fitting Plug to the working length. A 1-mm threaded tip holds the GP Plug on the Carrier, and immediately behind the Plug the Carrier has a plugger-like surface to push the Plug to working length.

The SimpliFill Apical GP Plug fits the apical preparation tightly—like a cork in a bottle. To achieve this excellent fit the apical part of the canal must be clean, precisely sized, and shaped correctly.

THE SIMPLIFILL TECHNIQUE

The following steps demonstrate canal obturation using the SimpliFill technique. Actual clinical cases depicted in Figures 3 through 6 were performed by Dr. Wildey.

Step 1. Check the Fit of the Apical GP Plug

Figure 7. Trial fitting the SimpliFill Apical GP Plug. After a few cases this step is typically skipped.

Trial fitting is simple and easy. If the Plug (same size as apical preparation) starts to feel snug within 1 to 3 mm of working length, this indicates a correct fit (Figure 7). We don’t trial fit any more, and most dentists also skip this step after a few cases because they know that the fit is predictable. AH Plus, an epoxy resin from DENTSPLY, is recommended for SimpliFill and was used in all the cases.

Step 2. Place the Apical GP Plug to the Working Length

Figure 8. The Apical GP Plug is condensed to WL. The tight “press fit” requires a pushing force, “like putting a cork in a bottle.”

Place sealer in the apical part of the canal with a paper point (use whatever you prefer) and also coat the Plug. After inserting the Plug into the canal, slowly advance it apically without rotating the handle (Figure 8). As the Plug enters the apical zone  you will feel a resistance and, because of the tight fit, will have to exert some force to move the Plug to working length (WL). This is good; you want to feel that nice tight fit.

Step 3. Release the GP Plug From the Carrier

Figure 9. The Apical GP Plug is released from the Carrier by turning handle counterclockwise.

With the Plug at WL, leave it there by turning the Carrier handle counterclockwise and removing the Carrier from the canal (Figure 9). This completes the procedure if a post is to follow.

As a quality assurance measure, if the Plug is too large for the preparation, it will bind well short of WL, and if it is too small it will just spin when the Carrier handle is turned (it will not release from the Carrier). There is no guessing. If the clinician leaves the Plug too short of WL it’s a non-issue; remove it with a Hedstrom file or drill it out with LightSpeed instruments.

Step 4. Fill the Remainder of the Canal With Sealer

Figure 10. The canal is filled from the GP Plug to the canal orifice with sealer using the SimpliFill syringe and needle. Simple and easy.

Because none of the cases shown required a post, the remainder of the canal had to be filled. Obturating the empty middle and coronal thirds of the canal can be done in many different ways. For those just starting to use SimpliFill, we recommend the simplicity and predictability of syringing sealer into the canal (Figure 10) and placing gutta-percha Backfill Cones into the sealer (see Step 5).

Figure 11. The SimpliFill Backfill Syringe and Needle. The small diameter needle allows the tip to contact or almost contact the top of the Apical GP Plug. Filling the canal from the “bottom up” helps avoid incorporating air bubbles in the sealer.

Fill the remaining space with an epoxy resin sealer—easily done with a SimpliFill syringe and a narrow diameter needle (Figure 11). The needle is moved apically until you feel it contact the GP Plug (ideal) or feel it bind on the canal walls short of the Plug. Then, sealer is slowly expressed until it appears at the canal orifice. Continue injecting the sealer while withdrawing the needle from the canal. Placing the sealer as close as possible to the Plug usually avoids trapping air in the canal.

Step 5. Place the Backfill Cones

Figure 12a. The first Backfill Cone, advanced through the sealer, is the same size as the Plug and must contact the Plug. Additional nonstandardized cones should be placed to fill any remaining space.	Figure 12b. Remove excess gutta-percha.

The first Backfill Cone is inserted into the canal and advanced through the sealer until you feel it contact the Apical Plug (Figure 12a). The purpose of the Backfill Cone is to make future posting or re-treatment safe and easy. The Backfill Cone, imbedded in the sealer and contacting the Plug, provides a continuous path of gutta-percha from the canal orifice to the WL. We could have problems making a post preparation or re-treating if only the hardened sealer filled the canal from the orifice to the Plug.

The very first Backfill Cone is a standardized cone, and its size is the same as the Apical Plug. Space permitting, additional nonstandardized cones should be added as space fillers. Sealer is easier to deliver and more fluid than warm gutta-percha. It flows freely to fill empty spaces. Because sealer flows freely and three dimensionally, lateral or vertical forces are not necessary for three-dimensional obturation.

Figure 13. The Hot Tip Gutta Cut is used to remove excess gutta-percha. It enters the mouth cold and is heat activated momentarily with a button. It cools rapidly and is removed from the mouth cold.

Note that all canal obturations (Figures 3 through 6) have a homogeneous appearance in the radiographs—without voids or signs of discontinuity between the Apical Plugs and Backfill Cones. The obturation time for each molar was 4 to 6 minutes. We remove excess gutta-percha with a new product called Hot Tip Gutta Cut (Figures 12b and 13). Placed in the mouth cold and removed cold, it eliminates any possibility of burning the patient, assistant, or doctor. The Hot Tip is easily activated with the touch of a button.

DISCUSSION

Because the SimpliFill technique does not require heat, it is important that the apical  canal size and shape are suitable for the Apical GP Plug. We want a tight fit, commonly called a “press fit.” To get a “press fit” the Plug is made slightly smaller at its tip and slightly larger at its back end—relative to the canal preparation. We like the feeling we get when condensing the Plug to WL. It gives reassurance that a nice tight seal is occurring. It’s like the seal achieved by a cork that is squeezed into the smaller space in the neck of a bottle.

This combination of a larger tapered Plug being forced into a smaller apical preparation requires a push to seat the Plug to the WL. This “push” helps the sealer move into  empty spaces that may exist in the apical 5 mm of the canal.

Whereas other techniques try to move gutta-percha into all the empty spaces, we prefer instead to have sealer do it. After all, it’s the sealer and not the gutta-percha that actually creates the seal. And, if there is extrusion of the sealer into the periradicular tissues, unlike gutta-percha it will be resorbed quickly. The role of gutta-percha is to take up space, not to seal a canal. It is well known that, by itself, gutta-percha is a poor sealing material—it doesn’t form a good seal against canal walls. This is why all accepted obturation techniques use sealer with gutta-percha.

We prefer not to use spreaders, pluggers, and heat because they require experience and expensive equipment to properly manipulate the gutta-percha correctly in the apical depths of the canal. There is the possibility of losing apical control by the misapplication of heat and compaction forces. Cracked roots also may result. We believe these techniques are better left for backfilling. Also of concern is the cooling shrinkage of gutta-percha.

Because the SimpliFill technique is different from other techniques, it is important to reiterate that the only purpose for heating and then vertically or laterally condensing gutta-percha is to move it in three dimensions. A sealer, having low viscosity, moves in three dimensions without the need for additional condensing.

CONCLUSION

SimpliFill is an easy system to learn and use. Together with LightSpeed, the matching Apical GP Plugs ensure a good apical seal.

Acknowledgment

The authors wish to thank Mr. Steven Senia, BSE, MBA, for his contributions to this manuscript.

References

1. Santos MD, Walker WA III, Carnes DL. Evaluation of apical seal in straight canals after obturation using the LightSpeed sectional method. J Endodont. 1999;25:609-612.

2. Namazikhah S, Shirani R, Mohseni A, et al. Dye leakage study: comparing conventional and new techniques. CDA J. 2000;28:435-442.

Dr. Wildey served 4 years as a general dentist in the US Air Force and is presently in an endodontic practice in the Dallas/Ft. Worth area in Texas. He is the primary author of two articles published in a major national dental journal.

Disclosure: Dr. Wildey is the co-inventor of the Lightspeed root canal instrument and SimpliFill obturation systems and a member of the LightSpeed Endodontics Board of Directors.

Dr. Senia is a diplomate of the American Board of Endodontics, a former Journal of Endodontics Editorial Board member, and a consultant for NASA’s space program. He has lectured throughout the world and published extensively. He can be contacted at DrSteveSenia@aol.com.

Disclosure: Dr. Senia is co-inventor of the LightSpeed Intrumentation System and a member of the LightSpeed Endodontics Board of Directors.