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Endodontic irrigation: optimizing pulp dissolution from complex root canal systems

CE Publish Date: June 23, 2021
CE Expiration Date: June 10, 2024
CEU (Continuing Education Unit):2 Credit(s)
AGD Code: 070

Educational aims and objectives

This self-instructional course for dentists aims to show information regarding endodontic irrigation as well as details regarding a new technique.

Expected outcomes

Endodontic Practice US subscribers can answer the CE questions by taking the quiz to earn 2 hours of CE from reading this article. Correctly answering the questions will demonstrate the reader can:

  • Realize the factors that can cause irrigation failures during RCT.
  • Recognize some of the more recent systems in the marketplace for endodontic irrigation.
  • Realize some ramifications of inflamed pulp remnants.
  • Observe a novel in vitro irrigation model.
  • Realize the effect of different variables like concentration, temperature, and aeration on the dissolution efficacy of sodium hypochlorite.

Dr. L. Stephen Buchanan introduces a new concept in endodontic irrigation. Read all about it, and then take the quiz to receive 2 CE credits!

Dr. L. Stephen Buchanan discusses a new concept in endodontic irrigation

Endodontic irrigation is the most important part of root canal therapy (RCT), but I confess it has never been the most interesting part of the process for me because there is so little to see going on during irrigation.

All the other aspects of RCT have an easily visualized representation of procedural events — whether that is by direct magnified sight or indirectly, by mental visualization. When I am cutting tooth structure with a diamond bur spun at 200,000 RPM, I see most everything happening at the bur/tooth interface. When I’m directing a rotary file to cut through a canal, even when the file is mostly buried in the root, mentally visualizing the hidden part of the file is very straightforward as I know the file’s geometry, and I know the depth in the canal to which that file’s geometry has progressed. Having cut a 30/.06 rotary file within a millimeter of the canal terminus, I only need to view the instrument’s flute spaces to see where the file cut dentin in the canal, and I can clearly see the hidden surfaces of the just-shaped canal in my mind. Irrigation not so much.

Endodontic irrigation is now the most interesting procedural topic in the field, primarily because of two of the most recent entries into the market — GentleWave® (Sonendo) and BioLase irrigation activation procedures. GentleWave irrigation system forged new ground in endodontics, and both these are able to result in radically smaller instrumentation procedures. We are now seeing a remarkable number of lateral canal irregularities in vital cases — cleaned and filled through preparations as small as 13-.03. More often than not these treatment results look more like one of Walter Hess’ anatomic castings1 than the overcut RCT results we used to associate with excellence in endodontics (Figure 1).

Figure 1: Lower molar case with 15-.03* canal preparations, GentleWave cleaning, and Continuous Wave Obturation with bioceramic sealer. Note the uninstrumented but cleaned and filled cervical and apical bifurcations in the distal root (*Shapes by MiniKUT Files by PlanB Dental)

Fear inflamed pulp remnants

Irrigating canals aside, diagnosing irrigation failures can be very mysterious, and patients unlucky enough to have an incompletely treated tooth containing inflamed pulp remnants are also at great risk of receiving unnecessary RCT and extractions if a diagnostic failure follows. A well-done study2 showed 11% of patients in pain who saw an endodontist were not relieved of their pain within 6 months. Half of these didn’t need an RCT — they had myofascial pain; the other half needed a root canal (better); but half of these had RCT done on the wrong tooth, leaving the last quarter of these pain management failures to irrigation failures such as the cases in Figure 2.

Figures 2A-2D: 2A. This maxillary premolar was treated twice in 9 months without relief of the severe and persistent pain referred to the “endodontic zone” of her face (images shown left to right). 2B. By simply extending treatment to the terminus of the primary canal, all of her symptoms were resolved. 2C. This lower molar was treated short in the ML canal and overfilled beyond the MB and D canal termini. The patient had persistent pain referred to his left side endodontic zone for 18 months after RCT. 2D. The ML canal was retreated, completely resolving the patient’s pain and revealing the etiology — an untreated mid-mesial canal harboring a pulp remnant with its own periradicular blood supply. The overfilled roots were never revised

Several factors obfuscate diagnoses of irrigation failures. Start with the fact that pain referred from inflamed pupal remnants may refer to any teeth on the same side of the patient’s face, while percussing the offending tooth may elicit a different awareness at most. The first big tip-off — if you did thorough thermal pulp testing before entry — is the knowledge that treating the tooth alleviated the patient’s thermally induced pain, leaving the patient with spontaneous pain that can be severe. The surprising aspect is how long pulp remnants can stay alive, a function of their close proximity to the rich periradicular blood supply. There will seldom be PR lucencies visible in CBCT volumes, and they won’t get even slightly better on the most effective antibiotics like Augmentin or clindamycin. The diagnosis is made by reviewing the patient’s history and finding notation of severe pulpitis before the emergency access. Give the patient 400 mg of naproxen (Aleve®), wait 40 minutes, and if the pain has been relieved, schedule  the patient for the retreat. And do a better job of irrigating the second time.

Deliquesce the pulp

How long does it take to deliquesce (dissolve) an inflamed pulp out of a complex root canal system? Researchers have done many in vitro and ex vivo studies of canalar biofilms3, and while some understand the mission better than others, they have a pretty good idea of what it takes and how long it takes to kill most or all the bugs in a root canal. Regarding pulp tissue in lateral recesses, however, it is generally agreed that it is more difficult and takes longer to digest pulp in lateral recesses than it does to kill biofilm in a pool of slime.

The best pulpal irrigation studies have been done in teeth slated for extraction, splitting their roots open after delivery and using a SEM to view the exposed surfaces (Figure 3) or embedding, slicing, and viewing sections through a light microscope to view the canalar contents. I was inspired to design a novel in vitro irrigation model (Figure 4) by a surprising irrigation failure I had using the multisonic ultracleaning technology5 in a lower C-shaped molar. The most likely etiology I could figure for the tooth to remain sensitive after completion was inflamed pulp fragments remaining in the broad buccal isthmus between the MB and D canals. The first time an isthmus dissolution study was done in this new model that, theory was confirmed (Figure 5); at the end of the 5-minute NaOCl cycle, pulp analog remained.

Figure 3: SEM photos of root surfaces after closed-system negative pressure irrigation4 was run through the canal of this upper cuspid tooth. EDTA was used during instrumentation with a 30-.08 file to finish, then 30 minutes of NPI with 6% NaOCl, with a 15 second final rinse with EDTA. Contrary to other researcher’s findings, irrigating with NaOCl after EDTA showed no excessive etching or apparent weakening of dentin. The smooth dentin surfaces show no evidence of overetching by NaOCl because a final rinse with EDTA was used, leaving clean, smooth, and structurally intact dentin walls
Figure 4: Clear research simulation block (designed by the author) printed in two halves, placing thin-sliced porcine tissue (pulp analog) in the isthmus space between adjacent simulated canals before block halves are assembled with light-cure adhesive. After assembly, a platform for the multisonic technology was built on top of the pulp chamber, and cleaning was done as video footage was shot through a microscope. This qualitative research model offers insights about relative speeds of pulp dissolution in isthmus spaces between canals when different irrigation methods are used
Figure 5: The multisonic technology procedure digests the pulp analog in the isthmus space in 7.5 minutes of NaOCl irrigation time. The image (fourth from the left) shows pulp analog remaining after the 5-minute NaOCl GW cycle. As this unit’s 2-minute EDTA cycle and its 45-second distilled water cycles followed, none of the pulp analog was digested or affected in any way. When another molar procedure Instrument was brought in, the 1.5-minute vacuum check with distilled water (with full multisonic energy applied) did not further the removal either. It wasn’t until the NaOCl cycle came on for another 2.5 minutes that the remainder of the pulp analog was removed

Watching playbacks of the video recording through the clear isthmus block, as the prosciutto captured between the block halves was irrigated and digested by NaOCl, fascinated me, especially when I realized I could watch how different variables like concentration, temperature, and the surprise variable aeration effected the dissolution efficacy of sodium hypochlorite (Figures 5-7).

Figure 6 (left): Isthmus research blocks showing the difference in pulp analog dissolution times btn 6% (left) and 12% (right) NaOCl. Doubling the concentration increased the speed of dissolution by 33%; Figure 7 (right): Isthmus research blocks showing the difference in pulp analog dissolution times btn NaOCl at 70º F (left) and NaOCl heated to 106º F (right). Increasing the temperature by 33% increased the speed of dissolution by 33%

From a 40-minute time to dissolve the pulp analog with 6% NaOCl EndoVac irrigation (much of that time spent unclogging the EV needles), dissolution times were progressively shortened: 40 minutes to 30 minutes simply by reversing the direction of fluid flow, simultaneously eliminating the clogging problem inherent to using irrigation needles as vacuum pipes; 30 minutes reduced to 20 minutes by increasing the concentration of the NaOCl solution from 6% to 12% or by heating the solution to 109º F, and the dog-bites-man story of how simply aerating the solution halved the time to dissolution as air bubble cavitation exploding out the ends of the catheters imparting significant shear forces throughout the length of the canal.6

Applying all variables to shorten the time

Finally, I did a block test combining all four of those factors — concentration, the direction and volume of fluid flow, temperature, and aeration (Figure 9) — bringing the time to digest all the way through the isthmus pulp analog down to 10 minutes. This led to joining forces with Vista Dental to develop what we call the multi-canalar PulpSucker (PS) Closed-System Vacuum-Drawn Irrigation System (Figure 10).

Figure 8 (left): Isthmus research blocks showing the difference in pulp analog dissolution times between NaOCl with no air bubbles (left) and NaOCl with air bubbles (right). Aerating the NaOCl doubled the speed of dissolution — the most surprising results of these isthmus block studies; Figure 9 (right): Isthmus research blocks showing the difference in pulp analog dissolution times between room temperature NaOCl without aeration (left) and heated NaOCl with aeration (right). Heating and aerating the NaOCl tripled the speed of pulp analog dissolution when applied in a closed-system vacuum-drawn irrigation method of action
Figure 10: This extracted tooth was entered through five separate 1 mm access openings, one for each of four canals and a fifth opening directly into the pulp chamber as a setup for the obturation to follow and was mounted in a TrueJaw printed replica (DELabs) with impression material. A stage was luted to the tooth with a light-cure polymer, catheters were placed to ideal length in each of the four canals plus the fifth catheter into the pulp chamber through its separate side port, and the top plate was luted to the stage after X-ray confirmation of catheter position. The catheter manifold was hooked up to an IV bag of NaOCl, the line out of the Top Plate was hooked into the chairside vacuum system, and it was left to run for 15 minutes after which the canal system was obturated and the access openings restored. This is minimally invasive endodontics at its best
Figure 11 (top): The canals in this lower molar were minimally cut to 13-.03 MiniKUT File shapes, irrigated with the PS System for 18 minutes, and obturated, revealing a 6 mm mid-mesial canal exiting its own furcal POE. This canal was never entered with an instrument; Figure 12 (bottom): Close-up radiography shows a remarkable apical delta system at the end of the distal canal. Seeing 1-3 lateral canal aberrations filled is commonplace, seeing five lateral canals filled in the apical 2 mm of the roots is the ultimate proxy for irrigation efficacy


This new irrigation system and method has the following advantages:

  1. PS Irrigation supports MIE canal shapes and single visit RCT for all cases.
  2. It is multi-canalar and works in all 1-5 canals simultaneously.
  3. It takes 2-4 minutes of hands-on to stage.
  4. It takes 8-15 minutes of hands-off irrigation run time.
  5. Vacuum-drawn irrigation with 8% NaOCl is 100% safe.
  6. There are no capital costs; no maintenance costs.
  7. These are single-use, completely disposable devices.

Besides endodontic irrigation, Dr. L. Stephen Buchanan educates colleagues on a variety of other topics. Read more about him in this Educator Profile:

Author Info

L. Stephen Buchanan, DDS, FICD, FACD, Dipl. ABE, was valedictorian of his class at the University of the Pacific School of Dentistry and completed the Endodontic Graduate program at Temple University in Philadelphia, Pennsylvania, in 1980. Dr. Buchanan began pursuing 3D-anatomy research early in his career, and in 1986, he became the first person in dentistry to use micro CT technology to show the intricacies of root structure. In 1989, he established Dental Education Laboratories and subsequently built a state-of-the-art teaching laboratory devoted to hands-on endodontic instruction, where he continues to teach today. Through Dental Education Laboratories, he has lectured and conducted participation courses around the world, published numerous articles, and produced an award-winning video series, “The Art of Endodontics.” In addition to his activities as an educator and practicing clinician, Dr. Buchanan holds a number of patents for dental instruments and techniques.


Disclosure: Dr. Buchanan is a stockholder of Sonendo; he is the inventor and owner of the IP associated with the closed-system, negative pressure, positive outflow irrigation (PulpSucker) device described in this article, and he is PlanB Dental’s Clinical Director.


  1. Hess W, Zurcher E, Dolamore WH. The Anatomy of the Root Canals of the Teeth of the Permanent Dentition. London: J. Bale Sons and Danielsson; 1925.
  2. Nixdorf DR, Law AS, John MT, Sobieh RM, Kohli R, Nguyen RH; National Dental PBRN Collaborative Group. Differential diagnoses for persistent pain after root canal treatment: a study in the National Dental Practice-based Research Network. J Endod. 2015;41(4):457-63.
  3. Retamozo B, Shabahang S, Johnson N, Aprecio RM, Torabinejad M. Minimum contact time and concentration of sodium hypochlorite required to eliminate Enterococcus faecalis. J Endod. 2010;36(3):520-3.
  4. Schoeffel GJ. The EndoVac method of endodontic irrigation: Part 2—efficacy. Dent Today. 2008;27(1):82,84,86-87.
  5. Haapasalo M, Wang Z, Shen Y, Curtis A, Patel P, Khakpour M. Tissue dissolution by a novel multisonic ultracleaning system and sodium hypochlorite. J Endod. 2014;40(8):1178-81.
  6. Buchanan LS. Closed System Negative Pressure Endodontic Irrigation: A Serious Inflection Point in Root Canal Cleaning. Dent Today. April 2020.

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Continuing Education (CE)

The continuing education article below is available to subscribers of Endodontic Practice US. In order to earn continuing education credits, you must be a Free or Paid subscriber and complete a short quiz about the content of the article. Our Free CE is limited to only 2 free credit hours per year.

Purchase a subscription now.

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