Ahead of the Curve: Future Directions in Endodontics

The demise of endodontic treatment as a credible procedure in dentistry has been greatly exaggerated, to paraphrase Mark Twain. This is ironic in light of the fact that nearly every endodontic instrument and technique has been radically im­proved over the last 15 years. The concurrent rise of implant dentistry has occurred for many similar reasons, not the least being the greatly enhanced aesthetic and functional success rates seen over the same time period. However, to categorically say that placing an implant is better than saving a tooth with endodontic therapy is either naïve or self-serving by those who only do implant surgery or sell implant fixtures. As an endodontist who also does implant surgery, the question be­comes very simple: What is in the patient’s best interest?
To answer this question requires an understanding of the current advances and limitations of endodontic therapy. So, this article will present a viewpoint informed by what is technologically possible and biologically adequate in order to help our patients make the best decisions as to whether a tooth should be saved or replaced. In the end, I always ask myself what I would want done for me, or a loved one, and then the answer becomes pretty straightforward. The greatest difficulties in that regard come in treatment planning for teeth that have failing endodontic treatment begging the question, “Why did this fail?” Without an answer to that question, there is no way to conscientiously decide whether to save or sacrifice a tooth.

DIAGNOSIS AND CBCT IMAGING

Perhaps the greatest improvement in the specialty, relative to treatment planning endodontic failures, is the advent of cone beam computed tomography (CBCT) imaging. The traditional projection radiograph is a 2-dimensional (2-D) shadow of a Z Plane object. Three-dimensional (3-D) imaging overcomes this major limitation by allowing us to visualize the third dimension, while at the same time eliminating superimpositions. CBCT, also called digital volume tomography, is a new technique that produces 3-D digital imaging at reduced cost with less radiation for the patient in comparison to traditional CT scans.1 It also delivers faster and easier image acquisition. The first endodontist in the world (that I know of) to have his own CBCT machine is Dr. Yoshi Terauchi in Tokyo, Japan. Four years ago, he installed a CBCT machine in his office and has since preoperatively scanned every patient he consulted and/or treated. Dr. Terauchi is an exceptionally gifted endodontist (he can get any broken file out of any root) and while I understood the advantages of volumetric im­aging for certain cases, I thought that he was a bit excessive in scanning every case. That was before installing an Accuitomo CBCT (J. Morita USA) machine in my own office.

Figure 2a. CBCT preoperative view of buccal root structure of upper second molar showing the MB and DB canals merging and bifurcating in the apical third.	Figure 2b. Postoperative radiograph showing that anatomy shaped and filled. Having the volumetric imaging beforehand inform­ed the requirements for successful treatment.
Figure 3a. Periapical radio­graph of maxillary central incisor showing no definitive PA lesion (compared to gener­al­ized, mottled lucencies).	Figure 3b. CBCT saggital image showing a very distinct and large PA lesion.

My best analogy here is when endodontists got their first microscope thinking that it was only really needed for doing endodontic surgery. Shortly into the experience, most of us realized that to do any case without the perfect light and multiple levels of magnification provided by an operating microscope was foolish and needlessly difficult. I am finding more and more cases every week that are better diagnosed, treatment planned, and treated with 3-D imaging on board.
Being able to see bone lesions in all dimensions is a huge advantage (Figures 1a to 1d)! Spiral fractures—often difficult to probe—become obvious with CBCT. Seeing the position of roots and adjacent structures like sinus spaces and nerve bundles in 3-D is a beautiful setup for surgical retreatment. However, with the very tight resolution provided by J. Morita’s CBCT machine, complex root canal anatomy is easily seen, so fourth canals in upper molars are immediately ruled in or out; and if present, they are far more easily located. Lateral canals, amazingly enough, can often be seen preoperatively in vital cases, giving the clinician greater motivation to effectively irrigate the root canal system after shaping (Figures 2a and 2b). Beyond these uses, I was really blown away by how many periradicular lesions are unseen on standard 2-D images—ones that are dramatically obvious in CBCT images (Figures 3a and 3b).2
The small field-of-view acquired by the Accuitomo (compared to other CBCT machines) exponentially re­duces absorbed radiation to the patient down to 8 to 12 µS (micro Severs)—less than an analog panoramic image. As a result, I can literally scan “at will.”3 When I installed the unit I expected it to be most useful for my implant cases, but found that it was more important for my endodontic cases.
Does having a CBCT machine de­fine an endodontist as an excellent clinician? No, of course not. However, just as it was with operating microscopes in the 1990s, those endodontic specialists who have them will be able to do things that those without cannot.

Figure 4. CT reconstruction of me­sial root of a mandibular molar show­ing a large isthmus and 4 apical portals of exit.	Figure 5. Mandibular molar with very simple me­sial canal anatomy that required a single 20-.06 GTX File to shape; and a very complex distal canal showing several abruptly curving canal impediments that required prebent negotiating and shaping files to prepare.

CONCEPTS FOR PREDICTABILITY

The most important concept re­quired for predictable endodontic therapy results (after correct diagnosis and treatment planning) is understanding that the more thoroughly we can treat this complex avascular system, the more often root canal therapy works. This has been understood by some clinicians (most exceptionally and brilliantly taught, in our time, by Dr. Herbert Schilder) since the late 1900s4, but remarkably is not yet understood by all clinicians today.
That’s just crazy (Figure 4). It’s the most fundamental concept in the whole field of endodontics. It’s the “elephant in the living room,” and it defies all logical consideration. However, as more progressive educators slowly take over our teaching programs, advancements in this regard are encouraging. Unfortunately, there are still itinerant lecturers who corruptly give permission to general dentists to treat just parts of root canal systems.
This is very upsetting. In my opinion, the next time someone in a lecture tells you that a cold gutta-percha single cone filling technique (typically rationalized because there is a sealer spinner used) is sufficient, you should consider walking out of the auditorium. You can three-dimensionally condense warm gutta-percha or a synthetic thermoplastic resin into every fin, web, isthmus, and lateral or accessory canal, in seconds (through remarkably conservative coronal shapes) if they have been properly cleaned and disinfected during the irrigation phase of treatment.
Conceptually, many general dentists and some specialists, are still laboring under mistaken directives given to them in dental school; most critically the fear of treating root canals to and through their terminal points.5 Why would dentists fear taking a small file through the end of a root canal, when implant surgeons cut through patients’ jaws with massive drills? This one concept cannot be overstated: without carrying treatment to and through the ends of primary canals we have no chance of even approaching predictable results.6,7 However, if you practice in an area of the country where this is verboten, you just might think implants are more predictable than endodontic therapy. For those of us who treat the whole root canal system, en­dodontic therapy works at least as often as implant placement, takes less time to completion of the restorative effort, and costs the patient half as much.
The fact is that virtually every root canal can be negotiated and treated to length; if dentists use a lubricant during this initial procedure (not hypo­chlorite or aqueous EDTA) and use a small enough file in the first pass to length (a No. 08 in small canals and a No. 10 in larger canals).8 The only other barriers to patency are impediments such as apical irregularities, or abrupt bends in the canal requiring the very tip of files to be bent accordingly (Figure 5). While these concepts of treatment are not new to dentistry, they are yet to be universally taught.
Conceptually, it is also important to remember that root canal systems, especially in molars, are complex enough that all surfaces of these spaces can never be cleaned with files without destroying the structural integrity of the tooth. Consequently, irrigating them effectively and three-dimensionally obturating them to the best of our abilities is critical for predictable clinical success. Ironically, the astounding reduction of time (from 30 minutes down to one minute) provided by the advent of rotary instrumentation has resulted in an increase in irrigation failures. Without a commitment to these concepts, the latest new endodontic technology is irrelevant.

Figure 6. CT reconstruction of canals shaped with landed (right) and nonlanded (left) rotary shaping files. Note the dramatic apical ripping with the very efficient yet unsafe files vs. the fidelity of the final preparation shape to the original canal path created by the landed instrument (30-.06 GTX File).	Figure 7. Premolar and molar with significantly curved canals, straightened(ripped) during shaping with nonlanded fast-cutting rotary shaping files. Both treatments failed within 6 months and apical surgery was required since no conventional re­treat­ment could resolve the severe apical damage.
Figure 8. Mandibular molar shaped with variable-land GTX rotary files. The mesial canals were cut to a 30-.06 shape and the distal to a 40-.08 shape. Note the remarkable fidelity of the final shapes to the original canal path de­spite multiple curves in the mesial root.	Figure 9. A maxillary molar with a vertical root fracture in the MB root due to coronal over en­largement.

Figure 10. A maxillary premolar prepared with a single 20-.06 GTX File resulting in a very conservative coronal shape, yet showing a 3-D treat­ment result (lateral canal cleaned and filled).

INSTRUMENTS AND DEVICES 

Before discussing the advancements in this next section, I would like to point out that one of the greatest changes in endodontic devices (although not new) has been the development of apex locators. Despite their misnomer (apices have no direct relationship to the terminal points of canals), apex locators have changed endodontic therapy forever and for the better. Any dentist reading this who does not use an apex locator in the determination of every canal length they treat is spending more clinical time for a lesser result. With today’s technology, it takes more time to acquire a well-angulated length determination film than it does to find the length with an apex locator, and to shape and conefit the canal. My preference is to accomplish these treatment objectives (without a test length film), and then to confirm length with a conefit film after canal preparation has been completed. If you do not have one, consider getting an apex locator now, learn how to use it, lose the length determination film, and own the canal! I personally use the Root ZX (J. Morita USA) unit invented by Dr. Imao Sunada,9 a dentist from Japan. This apex locator is stable and easily read.
The most notable improvement in endodontic instruments has been the nickel titanium (Ni-Ti) rotary shap­ing file revolution. We have seen many changes in instrument design as the number of competitors has increased. One of the biggest, which is still going on, was the push toward file designs that cut fast but didn’t predictably pre­vent transportation or breakage. Unfortunately, the consequences resulting from ripping apical curvatures open are only seen in overfills, a coincidence usually mistaken for the true etiology of the ensuing failure—dangerous shap­ing files that ripped the apical architecture of the canal. While the funct­ional characteristics of file geo­metry are very complex, where every design advantage presents a disadvantage as well, we know that radial lands on file blades prevent (or greatly reduce) straightening of curved canals when compared to nonlanded (so-called “cutting blades”) flutes (Figures 6 to 8).10
Less understood, but more important than the fact that we can shape canals with a handpiece-driven file, is the capability (made possible by the strength and flexibility of Ni-Ti) to impart very specific shapes to our preparations with variably-tapered instruments.11 The improvement in speed and accuracy of variably-tapered shaping files over the serial step-back method is incalculable. A dental student of average skill now has the po­ten­tial to create a perfect shape in a root canal during the first attempt, when it previously took a naturally skilled student 250 to 400 cases to achieve predictable results. Also mis­understood is the advantage of limiting the extent of coronal enlargement, a function that most rotary file sets cannot provide (Figures 9 and 10).
The biggest and most recent change in the rotary instrument realm is the introduction of the new R-phase (rhombohedral) Ni-Ti metallurgy for file fabrication. This innovation, created by 2 heat treatment processes interspersed with cold working the wire, provides improved flexibility and much greater resistance to cyclic fatigue which is the most common cause of file separation. While this very significant evolution has improved that aspect of file function, maintaining fi­delity to the original canal path requires well-designed geometry to a­chieve its full potential. Geometry matters!
The next wave of innovation in the Ni-Ti rotary revolution is cresting towards rotary negotiating instruments. This could be very cool, however, there are several serious challenges blocking this objective. One is the necessarily small diameters of these instruments, which makes them prone to torsional failure. The other challenge is how to prevent ledging when handpiece-driven files meet an impediment requiring a safe tip (always) and a means to traverse that impediment. The initial entries to this new product category, with their small increases in tip diameters, will not solve these problems. However, solutions to these problems will hopefully be developed causing handfile negotiation to be a thing of the past.
After shaping is completed, the dentist’s attention must be directed to­wards cleaning canal spaces. Many den­tists doing root canal therapy do not understand the difficulty and importance of effective irrigation procedures. If you shape a root canal in less than a minute with 2 files (this happens all the time with current technology), and fill it immediately; you will see cases that never heal. This case experience is usually connected to a vital inflamed case that is shaped and filled without sufficient irrigation time.
The treatment result looks perfect with no periradicular lesions and no improvement on effective antibiotics, but the tooth loses its sensitivity to percussion only after a nonste­roidal anti-inflammatory drug has been taken. Virtually all of these cases had originally presented with very inflamed vital pulps. Ergo, the etiology is vital inflamed pulp tissue left in lateral or accessory canals. Tissues in these peripheral canal regions are close enough to the rich perir­a­dicular blood supply to stay alive, yet they are pathologic enough to never heal. Retreatment with more adequate irrigation time will usually allow subsequent success.
Despite many attempts, the dental manufacturer’s efforts to improve on the efficacy of sodium hypochlorite (NaOCl) and EDTA as cleaning solutions in root canal systems has been for naught. Unfortunately, efficacy with these solutions currently requires direct contact with all the walls in a shaped canal for a significant time period (20 to 40 minutes) in order to disinfect and dissolve organic tissue.
Many methods have been proposed to improve that efficacy, including heating of the solutions, sonic activation, and ultrasonic activation. The primary concern about ultrasonic ac­tivation has been that even at low-power levels, ultrasonic activation of a small file in a shaped canal (if not done carefully) will often result in an apically ledged canal becoming a serious impediment to ideal obturation. Sonic activation has been shown to be safer, and very helpful in cleaning molar isthmuses in coronal regions, yet it has been shown to be relatively ineffective in apical regions.12 Negative pressure irrigation (suctioning through the irrigating cannula) is a re­cently developed irrigation technique. This system, which differs significantly from traditional positive irrigation, has demonstrated promising results. Al­though more time consuming, it has been shown to produce a better cleaning and disinfection.13,14
Progress in resolving this clinical challenge has lagged the developments in shaping and obturation technologies because there is so much less awareness about the importance of clean­ing procedures. However, this is currently where the greatest re­search and development opportunities lie for dental maufacturers in the near future.
As to the current state-of the-art techniques in obturation, all available evidence (the number of clinicians using this method, the obturation results achieved, and the research done) indicates that centered condensation is it. Whether you fit a cone and drive through it with an electric heat plugger, or push a preheated obturator through a canal space, the stream­ing effect of the thermosoftened filling material will fill any anatomic complexity that has been cleaned during irrigation.
Single cone technique is from the early 1900s and lateral condensation is from the late 1900s. Centered con­densation is now the state-of-the-art technique in obturation.15-17 No other filling method can fill as well, in as little time, and through such small coronal diameters.
One last comment: there are several companies who trumpet laser-sized gutta-percha cones, and truth be told, they are more precisely sized. However, it is not the accuracy of the cone that determines apical accuracy of obturation. Rather, it is the accuracy of the canal preparation. With­out landed blades, files can only make a shape that is larger than the silhouette of the file. Apical accuracy of cone fitting requires a predefined shaping outcome.11

The Importance of Technique

Just a few notes about technique:

• Brilliant diagnosis and treatment planning is worth way more than good hands. Don’t retreat loser teeth!
• Technology is an empty bag in the hands of a poorly intended, poorly trained dentist.
• The wrong negotiation technique will block you out in one out of 3 vital cases.
• If you negotiate to the terminus of root canals in the presence of NaOCl (no lubricant), you are going to have to say you prefer to treat vital cases short—“I meant to do that”—because you will get no other consistent result.
• If someone taught you that a No. 10 K-file (without a lubricant) is the appropriate size to approach the terminus in a small canal, you need to help them understand that they don’t know their file from an orifice.
• If you have done root canal therapy in the last week without an apex lo­cator you have failed the IQ test.
• If you don’t know the balanced force technique of K-file manipulation, you could do better in tight canals.
• If you think it takes 5 to 8 rotary shaping files to ideally shape a root canal, you are listening to the wrong salesperson.
• If you have used any type of Gates Glidden bur in the last year, you are going to the wrong lectures.
• If you think any irrigation technique, no matter how much im­proved, is going to get the job done in 3 to 5 minutes, you have never looked at CT reconstructions of endodontic anatomy.
• If you have been told by an endodontist that carriers cannot be re­moved for retreatment, show them how to do it after you learn the 60-second method shown on my Web site, endobuchanan.com.

At the end of the day, technique is the art of endodontics. I would rather have a root canal treatment on my own tooth by a seasoned pro who is using the oldest, most mundane instruments but the best concepts and techniques, rather than a newly-minted dentist with the latest equipment, no real experience, no grasp of the conceptual basis for endodontic success, poor technique, or (worst of all) only armed with great confidence and self-esteem.
Regardless of where you practice, you will find no difference in the clinical outcomes if you ignore the anatomic realities of root canal systems. This is because root canals are all the same throughout the world (OK, they can be different in Asia). They are complex and can often be difficult to treat successfully. Hopefully, I have informed you about the very consistent success that can be expected when treating root canals to their full apical and lateral extents. The good news is that it has never been so straightforward or so efficient. In terms of the financial challenges occurring throughout the world today, elective procedures will be pursued less often and pain relief (endodontic therapy) will be seen to be more recession proof. Despite rumors to the contrary, this is literally the golden age of endodontics!

Acknowledgement

I would like to thank Dr. Nestor Cohenca, chair faculty practice and as­sistant clinical professor, University of Washington, for his assistance with the references.

References

1. Ziegler CM, Woertche R, Brief J, et al. Clinical indications for digital volume tomography in oral and maxillofacial surgery. Dentomaxillofac Radiol. 2002;31:126-130.
2. Estrela C, Bueno MR, Leles CR, et al. Accuracy of cone beam computed tomography and panoramic and periapical radiography for detection of apical periodontitis. J Endod. 2008; 34:273-279.
3. Cohenca N, Simon JH, Roges R, et al. Clinical indications for digital imaging in dento-alveolar trauma. Part 1: traumatic injuries. Dent Traumatol. 2007;23:95-104.
4. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am. 1974;18:269-296.
5. Cailleteau JG, Mullaney TP. Prevalence of teaching apical patency and various instrumentation and obturation techniques in United States dental schools. J Endod. 1997;23:394-396.
6. Holland R, Sant’Anna Júnior A, Souza V, et al. Influence of apical patency and filling material on healing process of dogs’ teeth with vital pulp after root canal therapy. Braz Dent J. 2005;16:9-16.
7. Izu KH, Thomas SJ, Zhang P, et al. Effectiveness of sodium hypochlorite in preventing inoculation of periapical tissues with contaminated patency files. J Endod. 2004;30:92-94.
8. Buchanan LS. Shaping and cleaning the root canal system. In: Cohen S, Burns RC, eds. Pathways of the Pulp. 5th ed. St Louis, MO: Mosby Yearbook; 1991:166-192.
9. Sunada I. New method for measuring the length of the root canal. J Dent Res. 1962;41:375-381.
10. Walsch H. The hybrid concept of nickel-titanium rotary instrumentation. Dent Clin North Am. 2004; 48:183-202.
11. Buchanan LS. The new GT Series X rotary shaping system: objectives and technique principles. Dent Today. 2008;27:70-74.
12. Sabins RA, Johnson JD, Hellstein JW. A comparison of the cleaning efficacy of short-term sonic and ultrasonic passive irrigation after hand instrumentation in molar root canals. J Endod. 2003;29:674-678.
13. Nielsen BA, Baumgartner JC. Comparison of the EndoVac system to needle irrigation of root canals. J Endod. 2007;33:611-615.
14. Hockett JL, Dommisch JK, Johnson JD, et al. Antimicrobial efficacy of two irrigation techniques in tapered and nontapered canal preparations: an in vitro study. J Endod. 2008; 34:1374-1377.
15. Peng L, Ye L, Tan H, et al. Outcome of root canal obturation by warm gutta-percha versus cold lateral condensation: a meta-analysis. J Endod. 2007;33:106-109.
16. Lea CS, Apicella MJ, Mines P, et al. Comparison of the obturation density of cold lateral compaction versus warm vertical compaction using the continuous wave of condensation technique. J Endod. 2005;31:37-39.
17. Lee M, Winkler J, Hartwell G, et al. Current trends in endodontic practice: emergency treatments and technological armamentarium. J Endod. 2009;35:35-39.

Dr. Buchanan is a Diplomate of the American Board of Endodontics and a Fellow of both the Inter­national College of Dentists and American College of Dentists. Dentists interested in his videotape series, “The Art of Endodontics,” and his hands-on laboratory workshops in Santa Barbara, Calif, can call (800) 528-1590. For more information related to this article, visit endobuchanan.com for GTX updates and answers to frequently asked questions indexed by topic. A free online CE course on the GTX System is available, as well as other topics. Questions concerning challenging cases can be directed to (800) 528-1590.

Disclosure: Dr. Buchanan consults for and holds patents to the GT and GTX System of instruments manufactured and sold by DENTSPLY. He also holds patents with the System B/Elements Obturation Device, Sybron Dental Specialties, and is the inventor of the Con­tinuous Wave of Condensation technique. He has no financial in­terest in any other products mentioned in this art