The previous 25 years have seen great strides in improving endodontic instrumentation1 and obturation methods,2 yet advances in our ability to clean root canal systems have been disappointing, to say the least. We have seen little improvement in the irrigating solutions we use and, until recently, no significant improvement in the application of these irrigants to root canal system (RCS) complexities.
In general, irrigation efficacy has suffered in proportion to the time saved by rotary instrumentation. When it took 10 to 20 minutes to shape canals with hand files—flushing with sodium hypochlorite between instruments—irrigants were in the molar RCS a total of 30 to 80 minutes of irrigation time, and they were remarkably clean by the time conefit and filling were initiated. When shaping times dropped to 1 to 2 minutes with rotary files, endodontists—myself included—began seeing an increase in short-term failures, and many reverted to multi-visit root canal treatment (RCT), having solved the unrecognized irrigation inadequacy with the application of calcium hydroxide between appointments.4
Unfortunately, these irrigation failures are obscure and difficult to diagnose. Typically, patients return after RCT completion, complaining that they are experiencing the same pain as before treatment. According to Nixdorf et al’s5 findings, 11% of endodontists’ cases reported in the National Dental Network were not pain-free within 6 months after completion of treatment—half of those attributed to misdiagnosing myofascial pain syndrome for irreversible pulpitis—as needless RCTs were done without addressing the original etiologies. In my experience, the other half were due to incomplete removal of inflamed pulp remnants (Figure 1).
Persistent post-RCT pain due to pulp remnants is typified by pain referral within the endodontic zone (between the malar eminence and the lower border of the mandible); no relief despite administration of Augmentin or Clindamycin; no periradicular lucencies seen in CBCT imaging; and, at most, slight to moderate percussion and/or biting sensitivity. The clincher is a presenting history of moderate to severe pulpitis. These inflamed pulp remnants can be too injured to recover and yet persist in vitality when located close to the rich periradicular blood supply.
Early on, I had several of these mysterious failures of my own, but having practiced endodontics for a decade before rotary files were introduced, I came to the realization that sodium hypochlorite (NaOCl) irrigation must be continued after the abbreviated instrumentation time that rotary files made possible. With that understanding, I have continued to complete nearly all cases in a single visit.
It’s All About Time
McComb and Smith3 got it right 43 years ago—solutions of NaOCl and ethylene diamine tetra-acetic acid (EDTA) are all we need to clean root canals, and they cost only pennies per milliliter—so it isn’t surprising that virtually all attempts to improve our endodontic cleaning capabilities have revolved around more effectively applying and activating those solutions. One of the most critical things to understand about NaOCl is that although it can kill any pathogen on a countertop or dissolve an entire broached pulp in a dappen dish in just 10 minutes, it requires much longer to achieve the same effect in a root canal—more like 40 minutes of passive NaOCl irrigation to achieve a 100% kill of resident bacteria and adequate removal of pulp remnants.6,7
Why so long? It’s a matter of canal geometry and fluid dynamics, coupled with the chemical dynamics of connective tissue hydrolyzation. Root canal systems harbor pulp tissue in longitudinal spaces that we can only rinse from coronal directions, so the pulp interface available for digestion by NaOCl may have a circumference of just 0.1 or 0.2 mm. Compare that tiny irrigation front to a broached pulp dropped in a pool of bleach. The pulp, shelled from its root covering, is actively dissolved on every lateral surface and is gone in dramatically less time.
The chemical dynamics that limit our ability to digest pulp in the lateral recesses of root canal systems are simply this: As soon as NaOCl hydrolyzes a bit of connective tissue (losing an oxygen ion in the process), it becomes inactive.8 While a pool of NaOCl can continually bring fresh, active chemistry to bear, the volume of solution available in canals at the dissolution front is severely limited. Irrigation efficacy in RCS spaces is further limited by the accumulation of gasses liberated by this process.
Much has been made of a supposed “Vapor Lock” (an accumulation of gas liberated by this chemical process) that requires negative pressure irrigation (NPI) to eliminate.9 However, my research shows that the gases displacing active NaOCl are simply and immediately removed by our age-old positive pressure irrigation (PPI) methods, preferably by using a side-vented needle (Figure 2). PPI, as taught by Dr. Herbert Schilder since the ’60s, uniquely revealed RCS complexity as his serial step-back instrumentation technique—with irrigation between the many hand files used—made for very effective irrigation due to the files repeatedly replacing inactive NaOCl with fresh, active NaOCl in the apical thirds of root canals.10 Schilder’s peers misunderstood his joy (and ours) around filling lateral canals with his methods, commenting inanely that they were filled with sealer instead of gutta-percha—totally missing the significance of filled lateral canals as proxy for irrigation efficacy.
Regardless, I am a fan of the EndoVac device (Kerr Endodontics) because it is impossible to cause a hypochlorite accident when the irrigation needle is a vacuum source. Very talented endodontists have shown exceptional clinical results with NPI.11,12 However, aside from the safety issue, I am convinced that PPI, when used as continuously as NPI is used in the EndoVac technique, delivers the same efficacy. The only limitation of PPI is that clinicians (myself included) are loath to irrigate for extended periods of time as it is not a cure for boredom. EndoVac’s contribution to better irrigation, in my opinion, comes from NPI’s inherent safety because it allows us to direct dental assistants to sit in and execute the extended irrigation routines that accomplish definitive cleaning.
Files Do Not Clean Canals
From the 1960s to the present day, dentists have believed that instrumenting canals cleans them, ergo Schilder’s coinage of the phrase “Cleaning and Shaping.” It turns out that files don’t clean canals; they actually make them dirtier. I was first relieved of this misconception when I read the classic irrigation research done by Baumgartner and Mader.13 In this study, they scraped only one side of single-root root canals in the presence of different irrigation solutions, then split the teeth to evaluate the results with scanning electron microscopy (SEM). When the canals were irrigated with distilled water, both sides were dirty. When they irrigated with just NaOCl and EDTA (as per McComb and Smith), both sides were clean. The surprise came when they irrigated with just NaOCl: The uninstrumented side was totally clean, and the instrumented side was dirty, confirming the fact that not only do files not clean root canals, but also that without EDTA irrigation following their use, files leave a layer of debris—a smear layer—on the dentin walls (Figure 3).
This realization completely changed my understanding of what we do and don’t accomplish with RC instruments in canals, as it irrevocably changed my shaping objectives during RCT. With this paradigm shift in my understanding, in 1994 I designed GT Files—the first variably-tapered instruments in endodontics—to have maximum flute diameters (MFD’s) of 1 mm so they would only cut a limited amount of coronal dentin in canals.14 Sadly, it was many years before the widely-held belief that cutting big coronal canal shapes improved irrigation was dispelled by Dr. David Clark–a restorative dentist—when he essentially said the emperor has no clothes.15
Activation: It’s All Been Missing an Important Point
Regardless, the greatest limitation of all these activation strategies is the fact that they only work in a single canal at a time and that they are uni-canalar in function. This little-recognized issue negates marketing claims stating that instead of a passive 40-minute soak time with NaOCl, negative pressure irrigation or sonic or ultrasonic activation might do the same job in just 5 to 10 minutes. When these irrigation enhancement methods are used in multi-canular teeth, clinicians must hang on to the activation instrument for 20 to 40 minutes in a 4-canal molar instead of letting a longer passive soak time do the job without much hands-on time required. Photon-Induced Photo-acoustic streaming (PIPS) was never shown to achieve its promised cleaning efficacy,16 but my primary attraction to it was its multi-canular approach to RCT cleaning. My good friend Dr. Daniel Czerny says the most effective way to activate NaOCl is to combine its use with espresso. Chill, have a cafe latte while your assistant freshens the solutions until cleaning is complete, and then head back in and finish the root canal treatment.
Several years ago, a new multi-sonic endodontic cleaning device, GentleWave (GW), was introduced by Sonendo, and the first thing that caught my attention was its multi-canalar approach. The GW procedure requires creating, with a light-cure polymer (Kool-Dam [Pulpdent]), a custom gasket (platform) on the tooth being treated so that the procedure instrument (PI) can be placed on it and operate in the RCS as a closed system. The PI creates a negative-pressure environment inside the RCS, allowing the machine to spray NaOCl at a very high backward pressure without risking a hypochlorite accident from solutions passing through the ends of canals and into periradicular tissues. At the end of the molar PI, a titanium tube projects into the pulp chamber just short of the pulp chamber floor, and this propagates multi-sonic energy that reverberates down canal spaces along the hard-tissue dentin surfaces, very effectively breaking intracanal debris loose.17
This is cleaning efficacy on a level not seen before, allowing canals with little or no instrumentation to be cleaned during the 8-minute procedure time consisting of a 1.5-minute cycle of distilled water cleaning, followed by a 5-minute cycle of 3.5% NaOCl cleaning, then finished with a 2-minute cycle of 8% EDTA cleaning. In Figure 4, a tooth with extensive internal resorption is shown before and after a GW cleaning procedure, exhibiting its dramatic irrigation efficacy.
Despite this, my research method (Figure 5) has shown that sonic, ultrasonic, and multi-sonic energies have little or no effect in the removal of pulp tissue. Figure 6 shows the results that proved to me that none of the pulp tissue analog in the isthmus blocks was affected in the least by the GW multi-sonic energy during H2O or EDTA cleaning cycles. Only during the GW NaOCl cleaning cycle was pulp tissue digested, teaching us that it’s all about NaOCl and time. It turns out that pulp tissue actually absorbs and dissipates sound energy so it is really only dissolved by NaOCl activity, not by the agitation of solutions.
With that in mind, consider the costs of this very cool, high-tech invention: (1) Direct costs of $80,000 for the GW console, $5,000 per year for maintenance, and $100 per case; (2) indirect costs, including clinicians’ hands-on time to build and trim a platform (3 to 5 minutes) and to hold the PI on the platform until the cycle is completed (8 minutes). That’s 11 to 13 minutes of hands-on time, costing $92 to $217 of a specialist’s time. Is it worth it? While it is worth it for endodontists who are currently doing 2-visit RCT (when it allows them to go back to single-visit RCT), it would be very nice if we could achieve the same outcome for less money.
PS Closed System Negative Pressure Irrigation
Is there an alternative? It turns out there is if we remember that NaOCl flow and time are the most important factors in pulp dissolution, all high- and low-tech activation considered. These thoughts inspired me to experiment with Closed-System Negative Pressure Irrigation (CSNPI) using the same research block seen in Figure 6 but without multi-sonic energy. Using EndoVac negative pressure cannulae occurred to me because of the well-documented dangers of pushing NaOCl out through the ends of irrigating needles18 and the absolute safety EndoVac delivers in preventing this iatrogenic outcome.
I found that placing EndoVac micro-cannulae near the ends of each canal, sealing them at the cavo surface of the tooth, and applying suction to them could draw NaOCl irrigating solutions—ported into the pulp chamber—continuously down the canals to be evacuated out of the tooth through the cannulae into the chairside vacuum system. The advantages of this approach were that this would be multi-canalar, that it would require little hands-on time for clinicians, and that it would be absolutely safe.
The attainment of these objectives was confirmed in the research block, but it was disappointing to find that it took 40 minutes to match the isthmus cleaning result seen with GW due to the negative pressure needle openings plugging up with analog pulp debris, severely limiting the flow of the irrigating solution. How to speed this up? The answer that occurred to me was to reverse the flow of irrigating solution.
The epiphany came when I realized that NaOCl exiting the ends of irrigating needles was only dangerous when it was pushed out by a syringe plunger. If it was passively pulled through the needles by vacuum pressure applied to the RCS (Figure 7), not only was a hypochlorite accident impossible, but it was also impossible for the needles to clog up. Once the flow of NaOCl was free of clogging impediments, this reversed CSNPI device digested all of the pulp analog in the simulated isthmus space (Figure 8) in just 13 minutes! Beyond that exciting result, the hands-on time required was just the 2 minutes needed to attach the staging ring (SR) to the tooth, insert the needles into each canal, and lute the vacuum insert into the SR.
Unlike the larger apical preparations required by EndoVac’s directions for use, the passive outflow of NaOCl from the 30-ga irrigating cannulae has an effect several millimeters beyond their ends, allowing canals with MIE shapes as small as 13-.06 (Traverse Files [Kerr Endodontics]) to be cleaned to their terminii.19
In summary, the benefits of PS System (DELabs/Vista) closed-system negative pressure irrigation are: (1) It is 100% safe; (2) it offers extensive lateral pulp removal in less than 20 minutes; (3) it works in MIE canal shapes; (4) it enables single-visit RCT; (5) it requires only a couple of minutes of hands-on time to operate; (6) it is a multi-canalar irrigation method; (7) it requires no capital or maintenance costs; (8) it is 100% disposable after the procedure is completed; (9) it requires no electrically-powered device other than a dental office chairside vacuum pump; and (10) it does not require that 20 to 40% of RCT fees be given to a high-tech development company.
- Buchanan LS. Single file shaping with GTX rotary files. Dent Today. 2001.
- Buchanan LS. 3D obturation in seconds with centered condensation techniques. Dent Today. 2005.
- McComb D, Smith DC. A preliminary scanning electron microscopic study of root canals after endodontic procedures. J Endod. 1975;1:238-242.
- Manfredi M, Figini L, Gagliani M, et al. Single versus multiple visits for endodontic treatment of permanent teeth. Cochrane Database Syst Rev. 2016;12:CD005296.
- Nixdorf DR, Law AS, John MT, et al. Differential diagnosis for persistent pain after root canal treatment: a study in the National Dental Practice-based Research Network. J Endod. 2015;41:457-463.
- Haapasalo HK, Sirén EK, Waltimo TM, et al. Inactivation of local root canal medicaments by dentine: an in vitro study. Int Endod J. 2000;33:126-131.
- Retamozo B, Shabahang S, Johnson N, et al. Minimum contact time and concentration of sodium hypochlorite required to eliminate Enterococcus faecalis. J Endod. 2010;36:520-523.
- Estrela C, Estrela CR, Barbin EL, et al. Mechanism of action of sodium hypochlorite. Braz Dent J. 2002;13:113-117.
- Schoeffel GJ. The EndoVac method of endodontic irrigation, part 2—efficacy. Dent Today. 2008;27:82-87.
- Schilder H. Cleaning and shaping the root canal. Dent Clin North Am. 1974;18:269-296.
- Heilborn C, Reynolds K, Johnson JD, et al. Cleaning efficacy of an apical negative-pressure irrigation system at different exposure times. Quintessence Int. 2010;41:759-767.
- Santarcangelo F. Endodontic irrigation via apical negative pressure: a five-year experience. Oral Health. 2012;102:10-39.
- Baumgartner JC, Mader CL. A scanning electron microscopic evaluation of four root canal irrigation regimens. J Endod. 1987;13:147-157.
- Buchanan LS, inventor. Endodontic treatment system. US patent 5,752,825. May 19, 1998.
- Clark D, Khademi JA. Case studies in modern molar endodontic access and directed dentin conservation. Dent Clin North Am. 2010;54:275-289.
- Olivi G, DiVito E. Photoacoustic endodontics using PIPS: experimental background and clinical protocol. Journal of the Laser and Health Academy. 2012;1:22-25.
- Haapasalo M, Wang Z, Shen Y, et al. Tissue dissolution by a novel multisonic ultracleaning system and sodium hypochlorite. J Endod. 2014;40:1178-1181.
- Becker GL, Cohen S, Borer R. The sequelae of accidentally injecting sodium hypochlorite beyond the root apex. Report of a case. Oral Surg Oral Med Oral Pathol. 1974;38:633-638.
- Buchanan LS. Rotary negotiation procedures. Dent Today. 2019;38:62-65.
Dr. Buchanan lives in Santa Barbara, Calif, where he maintains a practice limited to endodontics in the same courtyard as his hands-on training facility, Dental Education Laboratories. He has taught thousands of dentists how to perform state-of-the-art root canal therapy, most often with tools he has invented. He invented 3-D printed tooth and jaw replicas to accelerate hands-on procedural training, profoundly changing dental CE experiences. Dr. Buchanan can be reached at the website delendo.com.
Disclosure: Dr. Buchanan owns stock in Sonendo, Inc, and is the inventor of the PS (PulpSucker) Irrigation System.