Endodontic Predictability: “Are You Making the Right Decisions?”

Dentistry Today


The key to endodontic predictability is knowing what to do when and then how to do it. In any nonsurgical endodontic treatment, the dentist has ten essential and distinct decision making moments. The purpose of this article is to distinguish these decision points for the dentist, suggest how each decision builds on and influences the next decision, and to be clear about the importance of each choice point in influencing endodontic predictability. Each of the ten decisions are discussed first as a question (Q) and answer (A), and then summarized with a corresponding guideline.

Decision No. 1: Do Your Clinical Skills Match the Rules of Endodontic Predictability (Figures 1a and 1b)?
Q: Is endodontic predictability about what is good enough or about what is possible?
A: The purpose of endodontics is to cure or heal lesions of endodontic origin. Success or failure depends on the quality of the Endodontic Seal.1 Without the Endodontic Seal, endodontic predictability is left to other factors: quality of root canal system cleaning, resistance of the host to endodontic disease, biologic variability, presence or absence of bacteria, presence or absence of previous lesion of endodontic origin, or presence or absence of radicular symptoms.
In order to create the Endodontic Seal, it is important for the endodontic clinician to remember exactly what he or she is intending to seal in the first place. First, each dentist should know how many canals are typically make up the tooth being treated, and a quick and simple reference will often help missing an obvious canal.1 Second, the dentist should consult with toothatlas.com and examine the wide root canal system varieties that exist for the particular tooth that is going to be treated. The ToothAtlas reminds us that, in fact, teeth are really not made of canals. Root canal system anatomy is comprised of systems, labyrinths, and unpredictable complexities. Root canal systems are analogous to “banners in the breeze,” according to the late professor Herbert Schilder.2 Canals are a name and distinction given to the root canal system anatomy by dentists and, at best, are only an illusion of their true uniqueness and curvatures.
All endodontic anatomy is potentially significant. The first and perhaps most important endodontic decision is to slow down, respect nature’s fragile anatomy by using great restraint with the endodontic files, and continuously celebrate and embrace all of the root canal systems’ nuances. Develop the attitude that focusing on “what’s possible” in endodontic mechanics is energizing, increases endodontic predictability, and is personally satisfying.
Guideline No. 1: Mother Nature has been teaching us how to do endodontics for years. Be delicate; root canal systems are always curved, complex, and one of a kind. Listen to Mother Nature’s Rules of how to play the game.

Figures 1a to 1f. Endodontic Decision No. 1: Rules; and No. 2: Seeing. (a) Extracted tooth demonstrating nature’s dental curves. (b) Extracted endodontic failure cleared after centrifuge in Pelikan Ink. Silver cones sealed the portals of exit that they were cemented in but undiscovered portal of exit between silver cones allowed leakage from internal labyrinth of root canal system anatomy (red). Nature does not make straight lines or duplicates. Root canal systems are no exception. (c, d, e) Endodontists at the Center for Endodontics (Tacoma, Wash) benefit from Global Surgical observer scopes, enabling the dental assistant’s second set of eyes, intimacy with the delicate skills, superior anticipation, and collegial energy. (f) New Kodak 9000 3D CBCT recently installed at the Center for Endodontics. The cone beam instrument has the capacity to revolutionize endodontics in the same way as the operating microscope.

Decision No. 2: Is Your Endodontics Illuminating (Figures 1c to 1f)?
Q: Do you see and then believe, or do you believe and then you see?
A: The truth is that the answer is both: in endodontics when we see, we have to believe. The converse, when we believe, we see is also true. When we believe that anatomy is novel and mysterious, we are not surprised or foiled during endodontic mechanics. Nature gives us the microscopic roadmap to perform masterful endodontics.
So what is the best, most efficient, and superbly ergonomic way to see? It is what we see with the endodontic microscope. While the first significant endodontic decision is to know your endodontic anatomy, the second is to see your endodontic anatomy in an optimal way. In order to perform the endodontics of possibility, your second decision is simple: test drive the microscope, get trained, and purchase the microscope for your endodontic treatment…start to finish. The proof of the pudding is 99.9% of trained microscope users never return the microscope (Global Surgical Microscope Accounting Statistics).
Training in established microscope training centers comes as a significant added value when you purchase the microscope from the Global Surgical (globalsurgical.com/dental). The learning curve is not steep when procedures are first accomplished using previous illumination/magnification techniques; and then use the microscope to inspect first at lowest magnification. Almost always, the dentist observes areas of refinement or frank correction that are needed in any procedural step. Then it is only a matter of time before the dentist is seeing and doing at the same time versus doing blindly, then seeing, and then attempting to correct while in the blind again. The microscope makes delicate endodontic movements intentional, efficient, and safe.
`The biggest buzzword in endodontics, however, is not the microscope, although most master endodontists believe the microscope is still the profession’s best-kept secret. The next transformation in endodontics is the cone beam computed tomography (CBCT) imaging (Figure 1f). For the first time, the dentist can see a tooth and its surrounding conditions in 3-dimensions (3-D). In addition, the CBCT is the first step toward seeing the root canal system itself with the same kind of accuracy as the ToothAtlas is able to scan an actual tooth.
Guideline No. 2: Get trained in the mastery of the microscope and you will experience newfound control and confidence in unraveling the roadmap of endodontic anatomy.

Figures 2a to 2g. Decision No 3: Access. (a) Line diagram of anterior root canal system (lateral view). (b) Access with restricted access. (c) Incisal or essentially enamel triangle No. 1 removed. (d) Lingual or essentially dentin triangle No. 2 removed. (e) Both triangle Nos. 1 and 2 removed. (f) Line diagram of posterior tooth where distal canal has unrestricted dentin access but mesial canal requires removal of internal dentin triangle. (g) Line diagram illustrates how chamber calcification creates chamber triangles that are easily seen and can be removed with the illumination, magnification, and precision of the microscope.

Decision No. 3: Are You Designing Proper Access Cavities (Figures 2a to 2g)?
Q: Is it possible to prepare straight-line access and preserve appropriate ferrule?
A: Straight-line access is conceptually simple.3 Endodontic files should not be impeded by enamel and/or dentin that can by easily removed. In anterior teeth, there are often essentially 2 triangles. The first triangle is referred to as Triangle No. 1, which is essentially made of enamel (Figure 2c). The second triangle is referred to as Triangle No. 2, which is essentially made of dentin (Figure 2d). The dentist performing anterior endodontics must decide to remove these 2 triangles before ever attempting to begin the rotary GlidePath. Failure to remove one or both of these obstructive triangles is the most common anterior access error that endodontists observe in endodontics as performed by restorative dentists. It is the leading cause for beginning the cascade of technical errors leading to failure in predictably producing the Endodontic Seal.
Straight-line dentinal triangular impediments exist in posterior teeth as well but are more subtle and often overlooked. Anatomically, they develop due to chamber calcification during natural aging and/or pulpal trauma. Evidence of posterior dentinal triangular removal is when the endodontic file’s reference point is the same cusp as the root canal that is being cleaned and shaped. For example, if you are cleaning and shaping the palatal canal of a maxillary premolar, the reference cusp should be the palatal cusp. In other words, the angle of access should be the same as the angle of incidence. The file should “stand straight and tall” coming out of the access versus an angle.
Guideline No. 3: Design all access cavities to achieve straight-line access without compromising ferrule integrity.

Decision No. 4: Are You Willing to Learn How to Simultaneously Use Intention and Restraint in Order to Follow the Canal to its Terminus?
Q: How is the decision to learn how to “follow” canals is the third, and in many ways, the most important decision for optimizing endodontic predictability?
A: While eventually reaching the radiographic terminus of the root canal system is ultimately prerequisite to the Endodontic Seal, how and when to reach the end to the canal is the distinction that makes the difference in GlidePath management4 (Figures 3a and 3b). When a file does not easily follow down the entire length of a canal, it is due to 4 possibilities or a combination of these possibilities (Figure 3c). First, there may be pulp or necrotic tissue blocking the advancement of the file. Second, the angle of the access of the file may be different than the angle of incidence of the file. In other words, the curvature of the file does not sufficiently mimic that of the canal for the file to easily follow. For example, the dentist has placed a 5-mm length apical canal curvature on the file and yet the actual canal is an abrupt 1 mm turn, or perhaps an actual hook, as often is the case in maxillary lateral incisors, the DB root of maxillary molars, and the distal canal of mandibular molars. Third, the D1, or tip diameter, of the file is wider than the canal it is attempting to follow. Forth, the shaft diameter of the file is wider than the coronal portion of the canal. Restrictive dentin requires restrictive dentin removal before the file can follow deeper toward the radiographic terminus.5 Some endodontic teachers refer to this skill as “early coronal enlargement” or “crown down.”
Guideline No. 4: After removing coronal radicular restrictive dentin, follow your smallest file to the radiographic terminus. Never force or push. Irrigate copiously and after every instrument’s withdrawal. Be patient. The endodontic game is won or lost at decision No. 4.

Figures 3a to 3g. Decision No 4: Follow, No. 5: GlidePath, and No. 6: Rotary Shaping. (a) Small hand file follows to the radiographic terminus. (b) Obturated maxillary first molar. Note the rotary shaping and subsequent packing of the mesiobuccal canal follows the flow of the small hand file and preserves the position of the original portal of exit. Absolutely no apical transportation has occurred. (First molar endodontic treatment by Dr. Loubna Pla.) (c) Four dilemmas and 4 solutions during GlidePath preparation. (d) Small hand file following to radiographic terminus in wide apical curve. (e) ProTaper rotary (DENTSPLY Tulsa) wants to and can easily follow smooth GlidePath regardless of the extent of curvature. (f) Abrupt distal apical curve followed by small hand file. (g) ProTaper file is capable of abrupt turn shaping.

Decision No. 5: Are You Willing to Master the GlidePath so You Can Make Rotary Endodontics Safe, Predictable, and Efficient?
Q: Should you decide to make a glide preparation crown down or step back?
A: Without any doubt, the most significant decision for safe rotary endodontics is to first to create a successful GlidePath. GlidePath may be defined as a smooth-walled tunnel from orifice to physiologic terminus (Figures 3d to 3g). For most rotary systems, a loose No. 15 file that can be followed and then withdrawn using small then larger amplitude strokes defines the GlidePath.6,7 The watchword here is loose. It is not enough that a No. 15 can be “worked” to length; it must easily be able to follow to length. Extreme care should be used when advancing from a No. 10 file to a No. 15 file because the most apical diameter of a No. 15 file is 50% wider than a No. 10 file. Because of this significant jump in size, there is an increased chance for inadvertently creating a shelf, dent, or gouge in the GlidePath wall. This results in rotary danger. This error, along with a little added force, is a sure setup for rotary file breakage. Make a decision to always have a smooth, reproducible GlidePath and enjoy the knowingness that as long as you are careful, you never force, you inspect and clean flutes at every rotary file withdrawal, and you practice the single use of rotary files, that you will truly control your endodontic rotary shaping and it will be safe.
Guideline No. 5: A smooth GlidePath is the secret to safe and successful rotary shaping.

Decision No. 6: What Rotary Shaping System is the Right One for You (Figures 4a to 4e)?
Q: So many rotary systems and so little time: What really matters in rotary?
A: First, remember that the biggest difference in rotary systems is not the rotary system. It is the dentist using the system. Are you careful, do you follow the rotary companies’ specific directions for use for the rotary files that they produce, do you always use new files for every treatment, are you sufficiently irrigating, are you constantly cleaning and inspecting the file’s flutes to detect unwinding?8
Second, be aware of a company that changes its file design about as soon as you have learned the system. Any reputable system’s geometries should be able to stand the test of time. Choose a file line that has been around a few years and can demonstrate sustainability and consistency. Rotary endodontics is too challenging and too dangerous for you to be part of the market test. Let someone else do it with someone else’s patients. Not yours.
Third, the essential qualities you should look for in rotary endodontics are safety, simplicity, efficiency, and consistency. In total, the rotary file system should give you a sense of control. You tell the rotary file what to do; not the reverse, as in many file systems where the file is nothing more than a fixed taper drill. The only difference is that you are not drilling into wood; you are carving delicate human tissue. The file design you choose should reflect this understanding in every file in its sequence. Each file should have a specific purpose and you should be able to easily measure that purpose has been served.
Fourth, the best way to compare rotary systems is through your own education. Take the rotary systems that you are considering learning. Then collect 3 mandibular molars for each rotary system you want to test. Prepare access cavities and make a GlidePath in all mesial canals. Then compare the systems head to head with your dental assistant, who may also be a good and less biased observer. Shape the ML canal with one file system and the MB with another, and discover which is right for you. The best education in the world is your own!
Be sure to follow the directions for use. It will not take long to discover the rotary system that’s for you. It’s really that easy. It will be the system that puts you in control and actually does what it says it will do.
Guideline No. 6: Choose the rotary system that is best for you by testing them yourself. You will discover the truth about which rotary concept and technique is the safest, simplest, and most efficient.

Figures 4a to 4f. Decision No. 7: Cleaning, No. 8: Conefit, and No. 9 Oburation. (a) Conefit. (b) Image from ToothAtlas.com. (c) Pretreatment image of mandibular molar. (d) Perpendicular image of obturation. (e) Oblique image of obturation. (Endodontic treatment by Dr. Jason West.) (f) Tooth­Atlas image of typical atypical molar.

Decision No. 7: What Cleaning Techniques Should I Choose (Figure 4f)?
Q: What does 3-D endodontic cleaning mean and how do you do it?
A: The purpose of cleaning the root canal system is to remove bacteria, biofilm, smear layer, and any remaining viable and nonviable irritants that are capable of sustaining or creating lesions of endodontic origin where the root canal system’s portals of exit are not permanently sealed. Full strength sodium hypochlorite should be used in the development of the GlidePath and then switch to EDTA during rotary. Finish with the following irrigation sequence: EDTA to remove remaining smear layer, sodium hypochlorite to remove any remaining detached necrotic tissue, and alcohol to dry the root canal system prior to obturation. The EndoActivator (DENTSPLY Tulsa Dental) has been shown to significantly increase the effectiveness of all endodontic irrigants.9
Guideline No. 7: Irrigate and agitate irrigants constantly during cleaning and shaping. Remember, what the dentist takes out of the root canal system is as important as what he/she puts into the root canal system.

Decision No. 8: Should I Make a Conefit Prior to Obturation (Figure 4a)?
Q: “Is it necessary to validate your radicular shape before you pack?”
A: Is it necessary to make an accurate impression before you cast an onlay? Of course it is. In endodontics there is an old saying that goes like this: “You don’t get what you want; you get what you measure.” Regardless of your obturation technique: vertical compaction of warm gutta-percha, continuous wave, carrier-based, or lateral condensation, you need to know if you are ready. The conefit tells you that you are ready. In warm gutta-percha techniques, the conefit additionally allows you to modify the cone itself before compaction which gives you additional refinement in endodontic finishing.10
Guideline No. 8: Develop the skill of making an accurate conefit prior to obturation.

Decision No. 9: What Obturation Method Is For Me (Figures 4c to 4e)?
Q: How do you create the maximum cushion of warmed gutta-percha and mold it 3-dimensionally?
A: The easiest obturation method to learn is lateral condensation. The next is carrier-based. The next is continuous wave. And the next is vertical compaction of warm gutta-percha.
The easiest to control is, in the opinion of the author, in this order: vertical compaction of warm gutta-percha, lateral condensation, continuous wave, then carrier-based.
The method that gives you the most choices are in this order: vertical compaction of warm gutta-percha, continuous wave, lateral condensation, then carrier-based.
The best 3-D endodontic seal is achieved in the following order: possibly carrier-based first, then vertical compaction of warm gutta-percha, continuous wave closely behind, and then lateral condensation.
The most technique sensitive order is: vertical compaction of warm gutta-percha, carrier-based, lateral condensation, and then continuous wave.

Guideline No. 9: Choose an obturation technique where you don’t have to think too much. Obturation is a time to relax. It should not be a sporting event!

Figures 5a to 5d. Decision No. 10: Coronal Seal. (a) Heat wave of gutta-percha is twice the length (approximately 5 mm) as resin bonded materials (arrows). (b, left) Resin bonded obturation of mandibular molar demonstrating obturation of many fins and portals of exit. (b, right) One year post-treatment reveals radiographic vanishing of resin bond in mesial anatomy particularly but root canal system branch between the 2 distal canals is receding as well. (c, left) Pretreatment and post-treatment of vertical compaction of warm gutta-percha obturation. (c, right) Note: Kerr Pulp Canal sealer (Kerr) has been hydraulically packed into previously undiscovered 10 mm branch off of the distal canal. (d) Eight-year post-treatment image demonstrates complete healing of the lesion of endodontic origin and continued and complete presence of the seal.

Decision No. 10: What Should You Do About the All-Important Coronal Seal (Figures 5a to 5d)?
Q: Should you use the new resin bonding endodontic obturation methods or is this a complicated solution to a nonexistent problem?
A: The idea of bonding the endodontic obturation is truly desirous. However, the literature does not yet suggest the science sufficiently warrants a change in obturation material or technique. In addition, resin-bonding materials, regardless of manufacturers’ earlier claims, requires a change in gutta-percha obturation technique. Furthermore, there is concern that resin endodontic materials wash out over time. There has never been a magic bullet in endodontics, and resin obturation will not be the first. The astute endodontic clinician should, however, keep current with the endodontic literature because much effort is being given to improve the more than 100-year-old gutta-percha medium.
Lastly, if gutta-percha is sealed 1 to 2 mm short of the chamber, then the risk of coronal leakage is a moot point. If a superb coronal seal is made then there is no coronal leakage. So in the vertical compaction of warm gutta-percha and continuous wave techniques, stop backpacking 1 to 2 mm short of the chamber floor, clean away any visible endodontic sealer, etch, bond, and restore access in preparation of foundation and restoration. In carrier-based and lateral condensation techniques, gutta-percha will need to be removed 1 to 2 mm down into the canal after obturation.
Guideline No. 10: Be sure to finish your endodontic obturation by making a coronal seal. Coronal seal is essential to endodontic predictability.

This article has presented ten key decision moments that influence endodontic predictability: (1) the roles of understanding the game, (2) seeing, (3) access, (4) following, (5) GlidePath, (6) shaping, (7) cleaning, (8) conefit, (9) obturation, and (10) coronal seal have been reviewed. The intention of this article has been to emphasize the importance of clear thinking, decision-making, and properly sequencing skills when treating patients with endodontic disease. Study your choices carefully. Make the right decisions.


  1. West J. Endodontic predictability—“Restore or remove: how do I choose?” In: Cohen M, ed. Interdisciplinary Treatment Planning: Principles, Design, Implementation. Hanover Park, Ill: Quintessence Publishing; 2008:123-164.
  2. Schilder H. Lecture notes. 1975 Boston University Goldman School of Dental Medicine. Boston, Mass.
  3. Ruddle, CJ. Endodontic access preparation: an opening for success. Dent Today. February 2007;26:114-119.
  4. West J. Removing the mystery: treating multirooted teeth. Dent Today. December 2009;28:70.
  5. West J. Endodontic update 2006. J Esthet Restor Dent. 2006;18:280-300.
  6. West J. Rules of engagement: mastering the endodontic game, part 1. Dent Today. June 2006;25:94-101.
  7. West J. Rules of engagement: mastering the endodontic game, part 2. Dent Today. July 2006;25:108-112.
  8. West J. So many rotary systems, so little time: how do I choose? 10 questions to ask before making a decision. Endo Tribune. April, 2008;3:1-7.
  9. Ruddle CJ. Hydrodynamic disinfection: tsunami endodontics. Dent Today. May 2007;26:110-117.
  10. West J. Finishing: the essence of exceptional endodontics. Dent Today. March, 2001;20:36-41.


Dr. West is the founder and director of the Center for Endodontics. He received his DDS from the University of Washington in 1971. He then received his MSD in endodontics at Boston University Henry M. Goldman School of Dental Medicine in 1975. He is the immediate past president of the American Academy of Esthetic Dentistry and current president of the Academy of Microscope Enhanced Dentistry. He maintains a private practice in Tacoma, Wash. He co-authored “Obturation of the Radicular Space” with Dr. John Ingle in Ingle’s 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. He has recently authored “Endodontic Predictability” in Dr. Michael Cohen’s 2008 Quintessence text Interdisciplinary Treatment Planning: Principles, Design, Implementation. He is a thought leader for Kodak Digital Dental Systems and serves on the editorial advisory boards for 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 (800) 900-7668 or via e-mail at johnwest@centerforendodontics.com.

Disclosure: Dr. West is a co-inventor of ProTaper and Calamus Technologies (DENTSPLY Tulsa Dental).