Rules of Engagement: Mastering the Endodontic Game, Part 2

Endodontics can be considered a game, and as noted in Part 1 of this article (Dentistry Today, June 2006), the degree and consistency of endodontic success depends on the vigilance and resolve with which the endodontic game is played. The first article discussed 3 essential rules or guidelines for achieving successful endodontic treatment: The Game, Access, and Glide Path. This article discusses 3 more essential rules: Cleaning, Shaping, and Obturation. As noted previously, while these are not the only rules, they are the guidelines for creating masterful, efficient, energizing, and enjoyable endodontics.

CLEANING

The classic endodontic triad for success consists of cleaning, disinfection, and obturation. The cleaning and/or irrigation phase of endodontics is without a doubt currently the most neglected aspect of the endodontic triad. It is, however, one of the most promising. It is the “new frontier” in endodontics and is commanding considerable attention, research, and innovation.
With the wide acceptance, increased knowledge, and advanced skill level of rotary endodontic shaping, irrigation of any kind within the root canal system yields a much shorter duration of time than it did previously. Most dentists typically learned to “instrument one canal per hour.” This same canal received copious irrigation during that hour. It is possible that once the glide path has been established, canals can be shaped within a few minutes. Therefore, the clinician may have a multicanal tooth that has been shaped, cone-fit, and is ready for obturation. However, detached tissue, necrotic debris, and bacteria may still reside in the root canal system anatomy.
For example, the mesial canals of a mandibular molar may often house an isthmus that contains pulp “remnants” and can be easily observed under the microscope. These troughs and pockets of potential irritant can cause endodontic failure. The undesirable matter can be cleaned away with ultrasonics when it can be seen, but such material can remain deeper within the cross-bridging of root canal systems and in fins and branches that the irrigants may never thoroughly digest, or even touch. In addition, potentially significant lateral portals of exit may not be patent due to lack of sufficient irrigation and/or irrigation time.
As in all of endodontics, fundamentals are key. While new digestants and instruments are developed, the time-tested method of effective irrigation is the difference that makes the difference.1 Full-strength sodium hypochlorite is by far the best digestant of detached pulp tissue, and it is capable of killing bacteria within seconds, including the AIDS virus. It is inexpensive, simple, and can be purchased in the form of an odorless bleach. Any benchtop experiment will demonstrate the value of sodium hypochlorite. A “doubting Thomas” dentist can test this by slicing an extirpated pulp into 4 sections and place them into 4 different solutions, such as 100% sodium hypochlorite, 50% sodium hypochlorite, 100% sodium hypochlorite heated, and 50% sodium hypochlorite heated. The full-strength heated sodium hypochlorite will digest the pulp in less than half the time of the next combination. While sodium hypochlorite irrigated into the chamber at an elevated temperature quickly becomes the temperature of the body, the endodontic clinician should seek every advantage.
When the complexities of the root canal system are reviewed, such as in Brown & Herbranson’s Tooth Atlas (toothatlas.com), the observer is humbled to realize the infinite uniqueness of every canal system, and should be motivated to irrigate more and more, and also deep within the root canal system. Every advantage to maximize success needs to be taken because all anatomy is potentially significant in the life of a patient’s tooth. In the context that we humans are experiencing longevity into our 100s, and that we are going to have our teeth, it is realized that not only does endodontics have to be done at its very best, but it has to last a long time.

Figure 1a. Shaping. Original ProTaper 6-pack.	Figure 1b. New super-efficient ProTaper Universal, which includes F4 and F5 (DENTSPLY Tulsa Dental).

A successful sequence of irrigants is to first begin cleaning and shaping with 100% strength (ideally heated) sodium hypochlorite. The sodium hypochlorite is then alternated with hydrogen peroxide to elevate dentin mud in mandibular teeth; if the patient is reclined, this technique can also be effective in maxillary teeth. Once the glide path has been thoroughly established, introduction of EDTA, because it is an indiscriminate chelator, will soften glide path walls. This can only make the rotary shaping even safer. Clinicians have reported that dentin suddenly “cuts like butter.” With the super-efficient ProTaper rotary files (DENTSPLY Tulsa Dental), obvious shavings can be observed within the chamber itself (Figures 1a and 1b).
EDTA, therefore, is immediately introduced when the clinician shifts from manual  glide path to rotary shaping. Sodium hypochlorite can then be periodically alternated with the EDTA, and the root canal system is finished using 100% alcohol to ensure dryness and/or BioPure MTAD (DENTSPLY Tulsa Dental). MTAD is a mixture of tetracycline, an acid, and a special detergent. The purpose of MTAD is to remove the smear layer from all the walls of the root canal system and kill any remaining bacteria using a 5-minute rinse after cleaning and shaping, and prior to obturation.2

Figure 2. Irrigation. Stropko Irrigators fit easily onto triplex syringe (2 on far right).

A useful instrument to use at the end of rotary shaping to flush the canal with water is the Stropko Irrigator (Sybron Endo; Figure 2). This is a safe and ergonomically accessible irrigation system, and the Stropko tip can easily fit on any triplex syringe. After the cone-fit, the canal can be flooded with the desired finishing irrigant.
In order to increase irrigation effectiveness, the following 8 guidelines are useful:

•  increase volume
•  increase concentration
•  increase temperature
•  agitate
•  use combinations
•  change solution frequently
•  increase time of contact
•  irrigate deep within the root canal system with safe-ended irrigation tips (DENTSPLY Tulsa Dental).

SHAPING

The first step toward successful obturation begins with cleaning and ends with shaping. The late Dr. Herbert Schilder discovered that the secret to cleaning and shaping mechanics was “serial reaming, filing,3 and recapitulation.” Schilder referred to “progressive shaping.” He understood that each pass of a file should be a thoughtful pass with an intentional outcome. He understood that to attempt to create shape with one instrument was dangerous because instruments could break, and that endodontics deals with delicate human tissue, not blocks of wood. His method was so advanced it was simple. Current 21st century endodontic shaping recognizes that “less is more when evaluating armamentarium and directions for use. What is more important is to understand the principles of cleaning and shaping, and have the ability to adapt them to a different set of circumstances with each canal that presents itself.
The mechancial concept is  to “connect the dots” of the roughed out glide path from orifice to apical constriction, making a smooth, continuously tapering funnel from orifice to the terminal portal of exit. The radiographic result marks the achievement of Schilderís 5 mechanical objectives. This preparation generates the hydraulics of obturation, which enable the clinician to seal the entire root canal network without knowing its intricacies until obturated. Schilder used to say that we “discover the anatomy when we pack.” This fact is observed in almost every endodontic obturation. Most commercially available brands of rotary files have the outline form of a fixed taper. The risk of a fixed taper is that “taper lock” can occur, where the full length of the blades can “screw” into dentin. Consequently, the instrument can engage over many square millimeters of dentin and fracture without warning.
This author prefers a file system that incorporates “progressive shaping” (Pro-Taper, which refers to “progressive taper;”Figures 1a and 1b). Shaping files carve specific parts of the root canal system, and the finishers smoothly connect the dots of the radicular preparation. The mistake that many dentists make is to forget that shaping in endodontics really involves “a few thoughtful interventions.” Cleaning and shaping become efficient, effortless, and effective when this type of thinking and understanding occurs.
Determining the shape of rotary instrumentation is easy. If the flutes of the blades are filled with dentin shavings, then the dentist knows that exact shape has been created within the “block of dentin” that makes up the inner part of the root. If the apical flutes are not loaded with dentin shavings, then the dentist must advance to a wider-diameter apical instrument, or “false tugback” would potentially exist. Another error of rotary instrumentation is for dentists to think they are “drilling out” a shape. The technique of “brushing” is a useful method to remove restricted dentin away from furcal danger and make room for the easy introduction of finishing files.

Figure 3a. Obturation. Approximat-ing gutta-percha cone diameter to last finisher file.	Figure 3b. Gutta-percha cone fit.

When is shaping complete? The answer is, when the cone fits (Figures 3a and 3b). In the case of vertical compaction of warm gutta-percha techniques, several systems have matching gutta-percha cones and rotary files. If a carrier-based obturation is chosen, then plastic canal “verifiers” are used to confirm a specific shape in order to choose the corresponding and proper obturator.
What is the basic strategy for cleaning and shaping a multirooted tooth? Many dentists make the mistake of negotiating and placing instruments in multiple canals at the same time. This is usually a mistake, because it is more effective to divide and conquer. Also, it is impossible to concentrate fully on multiple canals at a time, and it is even more impossible to maneuver files in canals at the same time.
A more efficient strategy first involves discovery. Take the smallest file in your armamentarium, such as a 0.06, precurve the file, and simply begin to slide into all the orifi one at a time. If the instrument easily falls several millimeters into the canal, then that fact is noted. Obviously, a larger file can be used in the same manner in a larger canal. What typically will happen is that a mesiobuccal No. 2 canal is small, and when it calcifies, it calcifies from the crown toward the apex, so the entrance to the canal is often very small and restrictive. It will be noted that a 0.06 file may only slide into the canal 1 mm or so, if that. This being noted, then the clinician can focus on that canal or penetrate deeper with a dental bur or an ultrasonic instrument until the canal becomes wider, so that the small file easily begins to follow into the canal.
Once at the deeper depth, the sodium hypochlorite is already effectively cleaning that canal, since the chamber will be brimfull of the sodium hypochlorite. In order to benefit from the irrigation while the easier canals are cleaned and shaped, having some volume or space in the small canals gives a tremendous advantage. When the clinician does begin to focus on the more restrictive canals, they have become patent by virtue of the sodium hypochlorite being flushed through the chamber multiple times during the cleaning and shaping of the easier canals.
Once the discovery phase has been completed, then the clinician is interested in following the file to the radiographic terminus of one of the canals. This may be the easiest canal. Total concentration is required because the canals are not straight. They always have a curve, if not in the body, then at the apical terminus. These last few millimeters of any canal can be easily blocked or transported by using instruments that are too large or used without extreme caution and delicacy. The glide path, cleaning, and subsequent shaping require supple finesse and intention, while at the same time the clinician must always restrain from pushing or forcing.
Once the cone fit has been made to the radiographic terminus, the canal should be cut back 0.5 to 1.0 mm, depending on the curvature, length, and diameter of the canal. The longer, more curved, and thinner the root canal system, the closer the cone should fit to the radiographic terminus. If the canal is short, wide, and straight, the gutta-percha cone can be fit farther from the apical constriction, but no farther than 1 mm. The clinician can then shepherd the gutta-percha into this “open apex” condition.

OBTURATION

The essence of obturation is to fill a funnel that has the characteristic of “restrictive flow.” Restrictive flow is an engineering term that refers to the fact that if a fluid such as gutta-percha were to flow into a continuously tapering cone, pressure would develop on the walls of that cone. If there were openings in the cone, such as lateral canals, the apically flowing material will automatically flow into these patent spaces simply by virtue of the hydraulics (Figures 4a to 4h, 5a to 5d, and 6a to 6b). The concept in warm gutta-percha techniques is to “capture the maximum cushion” of warm gutta-percha and mold the medium apically and laterally. The metrics of endodontic success lie in observing 2-dimensional radiographs. The clinician cannot, after all, remove teeth and section them horizontally to evaluate the quality of the obturation.

Dentists must rely on a radiograph, and the expression of consistent and demonstrative lateral canals radiographically obturated suggests that the proper hydraulics have been achieved. The goal is to minimize the interface between gutta-percha and dentin. The interface can be reduced to the size of a red blood cell (which is approximately 10 µm) and filled with sealer. This fact was observed as early as the 1970s by Dr. Gary Grey in his Boston University thesis, The Capabilities of Sodium Hypochlorite to Digest Organic Debris From Root Canals with Emphasis on Accessory Canals. His work was before the time of the microscope and it was before rotary, and yet the principles of endodontic hydraulics still existed, though they were more difficult to achieve clinically. Today, however, all clinicians have the capacity to produce consistent exceptional endo-dontic results if they have the knowledge, the skill, and the willingness to accomplish them.

It is the last ingredient, willingness, that seems to separate clinicians more than any other quality. Most dentists have excellent skills, and most dentists are very intelligent. Sometimes the willingness to “do it right” depends on time. However, it is true that elegant endodontics can take time. Surprisingly, however, the relatively difficult canals have suddenly become extraordinarily easier with the proper knowledge and sequence of rotary shaping. Once a glide path has been generated in a more difficult canal, the shaping also can be achieved effortlessly. However, following the directions for use for any rotary system is absolutely essential because each rotary system is different. There is no study to prove it, but it is clear that every dentist is capable of breaking any rotary instrument from any company in the world. What makes the instruments safe is knowing how and when to use them. This cannot be overemphasized.
A new obturation system, Resilon (Resilon Research), is a potential dream-come-true.⁴ To date, however, the literature has conflicting reports on its efficacy, and there are no long-term reports on its success rate, since the material and techniques are only a few years old. Dentistry will have to wait a number of years, like with gutta-percha, to determine if these cases begin to reverse and ultimately fail. In order to perform due diligence, most clinicians should use this material as they would with any new technique, which is to take an arbitrary number of consecutive patients and obturate using the Resilon material. I have personally finished more than 100 “Resilon patients” and am presently recalling them, and will do so until I have 100 of them recalled with more than  a 2-year follow-up. I will then report this to the literature. Others, however, should consider measuring results in the same way.
It is important to note that in the vertical compaction techniques, the Resilon does not behave exactly like gutta-percha, and clinicians who are using the warm gutta-percha techniques should familiarize themselves with the nuances of the difference in Resilon heat wave length and duration, as compared to gutta-percha. Lastly, the Resilon attempts to solve a problem that many clinicians may not have, which is exposure of gutta-percha to coronal leakage. The literature has clear evidence that gutta-percha obturation requires a coronal seal for maximum success.^5-9 If the gutta-percha obturation is terminated short of the chamber, and the chamber is effectively protected with a variety of techniques and materials, then the argument that “gutta-percha leaks” may not be quite as strong, since it is not “exposed” to coronal leakage. Millions of gutta-percha obturations have been successful through patients lifetimes, and even though the material is more than 100 years old, this fact may actually be to its advantage because it will not be for another 95 years that we will have that kind of a history for Resilon or any other new obturation material that may be introduced. However, if Resilon does what the manufacturer says it does, then this would be an advantage, and in endodontics we need every possible advantage because of the wide variability of root canal system anatomy, patient healing capacity, coronal leakage, required life of the tooth, etc.
The late Dr. Sam Seltzer has been quoted as saying that endodontics is “a big issue about a little tissue.” He was right! Endodontics has made it that way because our leaders, teachers, and researchers crossed every t and dotted every i. We have success rates that rival any procedure that is done in all of dentistry. We are rightfully proud of our results and will continue to challenge what is possible.

SUMMARY

The rules of engagement are an overview of the essential elements needed to reconstruct endodontically involved teeth back to successful, healthy members of the dental arch that function and are biologically healthy, structurally strong, aesthetic, and valuable. Endodontics just keeps getting better and better, and the future of endodontic success is bright. Now more than ever patients value and appreciate dental aesthetics. Everyone wants to look good, smell good, and appear successful. Teeth will always play a major role in these human desires. The endodontic tooth can either be the “weakest link” or it can be as strong a link as any other healthy tooth. The choice is ours…if we play by the rules.

References

1. Baumgartner JC, Cuenin PR. Efficacy of several concentrations of sodium hypochlorite for root canal irrigation. J Endod. 1992;18:605-612.

2. Torabinejad M, Shabahang S, Bahjri K. Effect of MTAD on postoperative discomfort: a randomized clinical trial. J Endod. 2005;31:171-176.

3. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am. 1974;18:269-296.

4. Johnson WT, Gutmann JL. Obturation of the cleaned and shaped root canal system. In: Cohen S, Hargreaves KM. Pathways of the Pulp. 9th ed. St Louis, Mo: Mosby; 2006:372-375.

5. Torabinejad M, Ung B, Kettering JD. In vitro bacterial penetration of coronally unsealed endodontically treated teeth. J Endod. 1990;16:566-569.

6. Welch JD, Anderson RW, Pashley DH, et al. An assessment of the ability of various materials to seal furcation canals in molar teeth. J Endod. 1996;22:608-611.

7. Roghanizad N, Jones JJ. Evaluation of coronal leakage after endodontic treatment. J Endod. 1996;22:471-473.

8. Ray HA, Trope M. Periapical status of endodontically treated teeth in relation to the technical quality of the root filling and the coronal restoration. Int Endod J. 1995;28:12-18.

9. Pisano DM, DiFiore PM, McClanahan SB, et al. Intraorifice sealing of gutta-percha obturated root canals to prevent coronal microleakage. J Endod. 1998;24:659-662.

The founder and director of the Center for Endodontics, Dr. West received his DDS from the University of Washington in 1971 and his MSD in endodontics at Boston University Henry M. Goldman School of Dental Medicine in 1975. He has presented more than 400 days of continuing education while maintaining a private practice in Tacoma, Wash. He co-authored “Obturation of the Radicular Space” with Dr. John Ingle in Ingleís 1994 and 2002 editions of Endodontics and was senior author of “Cleaning and Shaping the Root Canal System” in Cohen and Burns 1994 and 1998 Pathways of the Pulp. Dr. Westís memberships include The American Academy of Esthetic Dentistry, The Northwest Network for Dental Excellence, and The International College of Dentistry. He is the scientific endodontic editor for Boston Universityís CommuniquÈ and serves on the editorial advisory boards of The Journal of Advanced Esthetics and Interdisciplinary Dentistry, The Journal of Esthetic and Restorative Dentistry, Practical Procedures and Aesthetic Dentistry, and The Journal of Microscope Enhanced Dentistry. He can be reached at (866) 900-7668 or johnwest@centerforendodontics.com.

Disclosure: Dr. West maintains a royalty position with ProTaper Rotary Files, DENTSPLY/Tulsa.