The EndoVac Method of Endodontic Irrigation, Part 2-Efficacy

Part 1 | Part 2 | Part 3 | Part 4

Since sodium hypochlorite (NaOCl) has the capacity to cause catastrophic tissue damage when extruded into the periradicular vasculature^1-3, several new, exotic, and often very expensive endodontic irrigants have been marketed in order to replace this time proven endodontic irrigant. However, recent studies by Clegg⁴ and Dunavant⁵ have demonstrated that NaOCl alone is the only endodontic irrigant capable of significantly eliminating the biofilm associated with endodontic infections.  Dunavant studied NaOCl, SmearClear (SybronEndo), BioPure (DENTSPLY Tulsa Dental), chlorhexidine, and REDTA (Roth International), and reported: “Within the parameters of this study, both 1% NaOCl and 6% NaOCl were more efficient in eliminating E. faecalis biofilm than the other solutions tested.”
Why abandon NaOCl, now that it can safely be delivered to full working length via apical negative pressure that draws the irrigants down the canal and simultaneously away from the apical tissue?^6,7 The answer is simply because previous irrigation investigations have drawn the wrong conclusions from correct data. Will Rogers, Jr. said it best: “It ain’t what you know that gets you in trouble, it’s what you know that ain’t so.”

Figure 1. In 1971, Senia, et al8 demonstrated that sodium hypochlorite could not enter the critical apical area; however, Salzgeber9 demonstrated that Hypaque (x-ray above) could transcend the apical one third and enter the periapical tissues. The problem with the Salzgeber9 study is that Hypaque does not hydrolyze tissue, produce gases, and thus cannot create an apical vapor lock, see Figures 2 to 7. (Originally published as Figure 11 on page 397 in: Salzgeber RM, Brilliant JD. An in vivo evaluation of the penetration of an irrigating solution in root canals. J Endod. 1977;3:394-398. Copyright Elsevier [1977]. Reprinted by permission.)

Consider Senia, et al’s classic 1971 in vitro study⁸ in which he demonstrated that sodium hypochlorite did not extend any closer than 3 mm from working length even after the apex was opened to a No. 30 size instrument. Contrast this study with Salzgeber’s in vivo study⁹ in which he used Hypaque (a radiopaque solution with virtually the same viscosity, surface tension, and specific gravity as 5.25% NaOCl) to delineate canal and apical irrigant penetration. Salzgeber⁹ concluded that by increasing the apical preparation size past a No. 30 and tapering the walls, the irrigant would be carried completely down the canals and into the apical tissue (Figure 1). Both of these findings are accurate, and when viewed together it would seem as though the critical size necessary to insure complete penetration of the irrigant to the apical termination is a No. 35 with an increased taper. Salzgeber⁹ wrote: “The study by Senia, Marshall and Rosen showed that little or no sodium hypochlorite reached the apical 3 mm when the root canals were enlarged to a no. 30 instrument. The current study showed that the irrigant reaches the apex when the canals are opened larger than a no. 30 file.” This also agrees with current research by Zehnder¹⁰ who, using transparent plastic blocks, demonstrated that only after the apical size reaches a No. 35 can one colored irrigant successfully mix with another during instrumentation.

Figure 2. Prior to initiating endodontic therapy there is always some organic material (vital pulp, necrotic pulp, liquefied necrotic pulp) in the root canal system.	Figure 3. If sodium hypochlorite is used as an irrigant during instrumentation, it is put in the pulp chamber and then instruments are placed to the apex. When the instrument works its way apically, it forces an “empty space” or cavity within the organic material—the desired effect of instrumentation.
Figure 4. When the endodontic instrument is withdrawn from the cavity it just created, sodium hypochlorite (shown as blue) is immediately drawn from the pulp chamber into the now empty cavity created by the instrument. This principle of fluid displacement/ replacement was discovered by Archimedes in the 1st century BC when King Hiero II asked him to determine the gold content of his crown.	Figure 5. Once the sodium hypochlorite enters the cavity surrounded by organic material, the tissue hydrolysis reaction begins immediately forming small gas bubbles of ammonia and carbon dioxide.
Figure 6. When the next larger endodontic instrument is placed apically, it displaces the microbubbles coronally.	Figure 7. When the endodontic instrument is withdrawn coronally, the gasses, which are closer to the apical termination than the sodium hypochlorite, replace the endodontic instrument, thus forming the apical vapor lock. Nothing can physically displace this apical vapor lock or gas pocket—see Figure 8, nor can acoustic microstreaming or cavitation dissolve the gas pocket since its composition is gaseous, not liquid.

The critical error in the Salzgeber⁹ study is that although Hypaque has many of the same physical characteristics of NaOCl, it does not chemically react with organic material and liberate abundant quantities of ammonia and carbon dioxide, as does NaOCl. Under in vivo conditions the gaseous mixture of ammonia and carbon dioxide is trapped in the apical region and quickly forms an apical vapor lock, similar to the same problem encountered in petroleum powered engines, into which further fluid penetration is impossible (Figures 2 to 7). Extending instruments into this vapor lock does not reduce or remove the gas bubble (Figures 8a and 8b). In 1971, Senia⁸ wrote: “The solution [NaOCl] in the canal was stirred and carried apically every 5 minutes by means of a No. 10 reamer.” The dichotomy is that even though he thought he was carrying the NaOCl to the apex, his own research proved him wrong!

Figures 8a to 8d. A plastic block with a simulated root canal instrumented to a No. 35/4% taper communicating with a cross drilled hole, sealed with tissue in sections a, b, and d, demonstrates several fluid dynamic issues. First, endodontic instruments cannot displace an apical vapor lock or circulate irrigants into the gas bubble: “a” shows an endodontic file attempting to carry irrigant into the apical vapor lock and “b” shows the same file withdrawn, clearly demonstrating that no irrigant has entered the apical vapor lock as per Senia.8 Second, “c” demonstrates that if the canal system is not sealed apically (no tissue present in block “c”), that irrigant is easily forced through the termination. This is a common defect in irrigation studies where the examiner fails to seal the apex during experimentation, thus skewing any results in favor of the irrigant. Finally, “d” illustrates a positive pressure sideport needle attempting to circulate irrigant into the apical vapor lock; although coronal flow is evident, no apical circulation occurs as per Chow.21

Figure 9. The EndoVac endodontic irrigation delivery system produces negative pressure directly at the apical termination via a micro cannula attached to the office HiVac. Twelve radially arranged micro holes (only 6 shown in this view) populate the last 0.7 mm of end of the micro cannula and serve to direct the irrigant flow and as a micro filter. As soon as the irrigant is drawn down the canals, it is sucked away from the apical tissue and into the HiVac system.	Figure 10. The Nielsen, et al study23 incorporated matched pairs of teeth imbedded in polyvinyl siloxane impression material. The traditional needle was placed at WL—2 mm, which placed its exit portal directly at WL—3 mm, the exact point of the coronal section. The EndoVac was placed at full working length, below both sectioning points. The red lines indicate the points of cross section.
Figure 11a. EndoVac Irrigation: This is the companion to the section shown in Figure 11b. It is the matched tooth from the same patient at the same level of cross section. It demonstrates a canal clean and free of either loose or adherent debris after using EndoVac irrigation.	Figure 11b. Traditional Irrigation: This cross section taken 1 mm from working length after using traditional techniques, demonstrates significant loose debris in the canal (arrows) as well as debris still adhering to the walls to the right of the loose debris.

Figure 12. E. faecalias study demonstrates no growth in EndoVac samples after Macro Irrigation, while traditional irrigation still produced positive growth. More interesting is the fact that zero growth was realized in the positive control after abundant saline circulated through the apical region. Note: This study only produced a planktonic E. faecalis growth, not a biofilm, thus the explanation for producing zero growth via saline alone.

Figure 13a. SEM with white dots at 1 mm increments was obtained by splitting a tooth following EndoVac irrigation of an apically sealed tooth. SEM (1,000x) is taken from a region 2.75 mm from the apical termination. Note the homogenous arrangement of clean noninstrumented calcospherites in this area. The tubular pattern at this level is consistent with normal tubular anatomy.	Figure 13b. SEM (3,000x) taken at 0.75 mm from the apical termination demonstrates completely clean walls at this level. Although the tubular pattern is irregular, yet normal as described by Mjor, et al25 the tubules are clear of organic debris or smear layer.

Another example of drawing the wrong conclusion from correct data occurs when an investigator fails to duplicate the complete clinical conditions in an in vitro study. In 1971, Senia⁸ duplicated the clinical endodontic condition by successfully sealing the apical termination with green stick compound, thus allowing the apical vapor lock to form. However, some current endodontic irrigation studies^11,12 fail to seal the apical termination, thus preventing formation of the apical vapor lock and allowing irrigants to flow freely through the apex.
This “open system” error in methods produces results that most certainly skew in favor of the irrigant being tested (Figure 8c). Interestingly, in one of these “open system” studies the examiners who demonstrated superior in vitro canal cleanliness using a revolutionary endodontic irrigant admitted that leaving open the apical termination during testing might have flawed the study.11 Many in vitro SEM, light microscopy, and microbiological studies^13-20 that did seal or “close” the apical termination before testing irrigation regimes have universally failed to demonstrate clean canal walls in the apical one third, or complete microbiological control. In 1983 Chow²¹ convincingly demonstrated the inability for endodontic irrigants to be carried much past the termination of the irrigation needle in a “closed canal” system (Figure 8d). In the discussion of his study, he defined the 3 criteria necessary for successful mechanical endodontic irrigation. The irrigants must: (1) reach the apex, (2) create a current flow, and (3) carry particles away.
Still another example of drawing the wrong conclusions is not applying correct scientific principles to a specific situation. Consider the erroneous idea that acoustic microstreaming or cavitation can clean any part of the apical portion filled with gas (apical vapor lock). Acoustic microstreaming is defined as the movement of fluids along cell membranes, which occurs as a result of the ultrasound energy creating mechanical pressure changes within the tissue. Cavitation is defined as the formation and collapse of gas and vapor filled bubbles or cavities in a fluid. This process (“cavitation”) results from the creation and collapse of microbubbles in the liquid.²² Acoustic microstreaming or cavitation is only possible in fluids/liquids, not gases. Once a sonic or ultrasonically activated tip leaves the irrigant and enters the apical vapor lock, acoustic microstreaming and/or cavitation becomes physically impossible. This would be like trying to fly a submarine above the water.
Since every clinical endodontic situation is a “closed system” (except those terminating directly in the maxillary sinus and not covered by the Schneiderian membrane), how does a clinician remove an apical vapor lock? How does a clinician achieve a safe current force of irrigant at full working length? How does the clinician remove debris from the apex? The answer to each of these questions is the same—place a small cannula, attached to the office HiVac, at the apex and aspirate out the gas and canal debris while by drawing fresh sodium hypochlorite to and simultaneously away from the apical vasculature (Figure 9). The efficacy of this method of endodontic irrigation will be demonstrated by reviewing histological and biological studies and a SEM examination of the apical 3 mm.

HISTOLOGICAL STUDY

This study examined matched pairs of single rooted teeth from the same person that were caries-free and did not have previous restorations. Each pair was randomly divided into 2 groups: one group was treated via traditional needle irrigation delivery, and the other was treated via apical negative pressure delivery (EndoVac, Discus Dental). The root canal system(s) were closed by imbedding the teeth in poly-vinyl siloxane impression material, and all teeth were shaped using Gates Glidden drills and Profile series 29 .04 taper rotary instruments (DENTSPLY Tulsa Dental) using a crown-down, continuous taper technique (Figure 10). Final irrigation for the traditional group was performed using a 30-gauge ProRinse side port needle (aka, Max-i-Probe, DENTSPLY) 2 mm from working length to express sodium hypochlorite or EDTA. Final irrigation for the EndoVac group employed the use of a 30-gauge micro cannula attached to the office HiVac and placed at full working length. In this group, irrigants were added coronally and pulled to full working length, and then simultaneously back out through the micro cannula and into the HiVac system. The teeth were prepared histologically, cross-sectioned at 1 mm and 3 mm (see red lines in Figure 10) from working length, and examined for remaining debris. The residual intracanal debris was quantified and statistically analyzed.
This study demonstrated that the EndoVac group (Figure 11a) produced statistically significant cleaner canals at 1 mm from working length than traditional irrigation (Figure 11b). However at the 3 mm level (the exact level where irrigant is expressed from the ProRinse needle), there was no significant difference. To the untrained researcher, it is easy to interpret the results as no difference at 3 mm above the WL, and then continue down the wrong logic path and propose that there would be also no difference if the ProRinse could reach WL.
Upon more careful analysis, the reason for the statistical result of no difference is due to the extremely large variability of the ProRinse, as indicated by the large standard deviations (Percent of Debris in Field: Mean = 2.285%, Std. Deviation = 6.26). In contrast, the EndoVac system produced highly consistent results and therefore tight standard deviations (Percent of Debris in Field: Mean = 0.421%, Std. Deviation = 0.86). So, the statistical analysis used in the Nielsen, et al²³ study paper is not able to discern the obvious difference. There is also the practical safety issue of expressing irrigants under positive pressure immediately adjacent to the periapical vasculature.

BIOLOGICAL STUDY

Siquera demonstrated the difficulty in obtaining post-preparation zero growth cultures with sealed root canal systems infected with E. faecalis, and sometimes shaped to extremely large 12% tapers.²⁰ Before deciding to proceed with development of the EndoVac system, a pilot study was designed to examine the possibility of obtaining zero growth cultures using the above cited Siquera protocol to produce a closed root canal system and proper E. Faecalis inoculation; however, the test teeth were prepared only to conservative 4% tapered preparations. Since this was a pilot study, it lacked a negative control and the sample sizes were too small to derive definitive statistical data, yet the data is consistent, and when combined with SEM examination, the study demonstrated the merits of proceeding with full development of the EndoVac system of apical negative pressure.
Figure 12 shows that 2.5% and 5.25% concentrations of NaOCl were used for 2 minutes and delivered via either apical negative pressure or traditional positive pressure. It demonstrates that all specimens were successfully and consistently inoculated, and a consistent drop in CFU occurred during the instrumentation phase in both groups. The first apparent difference occurs at the termination of the traditional technique, which corresponds to macro evacuation with the EndoVac method of endodontic irrigation. At the macro phase the EndoVac system produced zero CFU using either dilution of NaOCl. A remarkable difference occurred at the termination of the micro cannula phase of irrigation, when no CFU were recovered from the saline positive control. Why? Since the E. faecalis was only grown for 24 hours, biofilm could not form, and because the microorganisms were simply planktonic, the abundant and rapid exchange of saline alone cleared the apical area, thus demonstrating each of Chow’s²¹ requirements for successful mechanical endodontic irrigation: reach the apex, create a current flow, and carry particles away.
This leaves open the question of removing biofilm, and these studies are currently in progress. However, biofilm does not differ chemically from other organic components found in the root canal. As a preview of upcoming results consider Figures 13a and 13b. This specimen was prepared according to the EndoVac instrumentation and irrigation protocol described by Nielsen, et al²³ but was split longitudinally for SEM examination. Figures 13a and 13b are consistent with normal dentinal tubular anatomy in the apical 3 mm²⁵, and in both areas there is no evidence of organic debris or smear layer along the walls, and the tubules themselves are free of debris.

CONCLUSION

Since the dawn of contemporary endodontics dentists have been squirting sodium hypochlorite into the root canal space and then proceeding to place endodontic instruments down the canal in the errant belief that they were carrying the irrigant to the apical termination. Biological, SEM, light microscopy, and other studies have proven this belief to be invalid. Sodium hypochlorite reacts with organic material in the root canal and quickly forms micro gas bubbles at the apical termination that coalesce into an apical vapor lock with subsequent instrumentation. Since the apical vapor lock cannot be displaced via mechanical means, it prevents further sodium hypochlorite flow into the apical area. Injecting irrigants is limited near to the tip of the injection needle, and the closer the needle tip is positioned to the apical tissue the greater are the chances of apical extrusion. Acoustic microstreaming and cavitation are limited to liquids and have no effect inside the vapor lock. The only method yet discovered to eliminate the apical vapor lock is to evacuate it via apical negative pressure. This method has also been proven to be safe because it always draws irrigants to the source of the vacuum—down the canal and simultaneously away from the apical tissue in abundant quantities. When properly used, the Endo-Vac is capable of producing the efficient and effective results described herein.

1. Bowden JR, Ethunandan M, Brennan PA. Life-threatening airway obstruction secondary to hypochlorite extrusion during root canal treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006;101:402-404.
2. Witton R, Brennan PA. Severe tissue damage and neurological deficit following extravasation of sodium hypochlorite solution during routine endodontic treatment. Br Dent J. 2005;198:749-750.
3. Joffe E. Complication during root canal therapy following accidental extrusion of sodium hypochlorite through the apical foramen. Gen Dent. 1991;39:460-461.
4. Clegg MS, Vertucci FJ, Walker C, et al. The effect of exposure to irrigant solutions on apical dentin biofilms in vitro. J Endod. 2006;32:434-437.
5. Dunavant TR, Regan JD, Glickman GN, et al. Comparative evaluation of endodontic irrigants against Entero-coccus faecalis biofilms. J Endod. 2006;32:527-531.
6. Haas S, Edson D. Negative apical pressure with the EndoVac system. Poster presented at: American Association of Endodontists 2007 Annual Session; April 25-28; Philadelphia, PA.
7. Schoeffel GJ. The EndoVac method of endodontic irrigation: safety first. Dent Today. Oct 2007;26:92-99.
8. Senia ES, Marshall FJ, Rosen S. The solvent action of sodium hypochlorite on pulp tissue of extracted teeth. Oral Surg Oral Med Oral Pathol. 1971;31:96-103.
9. Salzgeber RM, Brilliant JD. An in vivo evaluation of the penetration of an irrigating solution in root canals. J Endod. 1977;3:394-398.
10. Zehnder M. Root canal irrigants. J Endod. 2006;32:389-398.
11. Torabinejad M, Cho Y, Khademi AA, et al. The effect of various concentrations of sodium hypochlorite on the ability of MTAD to remove the smear layer [published correction appears in J Endod. Jun 2003;29:424]. J Endod. Apr 2003;29:233-239.
12. Grandini S, Balleri P, Ferrari M. Evaluation of Glyde File Prep in combination with sodium hypochlorite as a root canal irrigant. J Endod. 2002;28:300-303.
13. Albrecht LJ, Baumgartner JC, Mar-shall JG. Evaluation of apical debris removal using various sizes and tapers of ProFile GT files. J Endod. 2004;30:425-428.
14. Usman N, Baumgartner JC, Marshall JG. Influence of instrument size on root canal debridement. J Endod. 2004;30:110-112.
15. O’Connell MS, Morgan LA, Beeler WJ, et al. A comparative study of smear layer removal using different salts of EDTA. J Endod. 2000;26:739-743.
16. Baumgartner JC, Brown CM, Mader CL, et al. A scanning electron microscopic evaluation of root canal debridement using saline, sodium hypochlorite, and citric acid. J Endod. 1984;10:525-531.
17. Mader CL, Baumgartner JC, Peters DD. Scanning electron microscopic investigation of the smeared layer on root canal walls. J Endod. 1984;10:477-483.
18. Berutti E, Marini R. A scanning electron microscopic evaluation of the debridement capability of sodium hypochlorite at different temperatures. J Endod. 1996;22:467-470.
19. Siqueira JF Jr, Rocas IN, Favieri A, et al. Chemomechanical reduction of the bacterial population in the root canal after instrumentation and irrigation with 1%, 2.5%, and 5.25% sodium hypochlorite. J Endod. 2000;26:331-334.
20. Siqueira JF Jr, Rocas IN, Santos SR, et al. Efficacy of instrumentation techniques and irrigation regimens in reducing the bacterial population within root canals. J Endod. 2002;28:181-184.
21. Chow TW. Mechanical effectiveness of root canal irrigation. J Endod. 1983;9:475-479.
22. Scientific overview: ultrasound terms. Celleration Inc Web site. http://www.celleration.com/therapeutic_ultrasound.html. Accessed November 26, 2007.
23. Nielsen BA, Craig Baumgartner J. Comparison of the EndoVac system to needle irrigation of root canals. J Endod. 2007;33:611-615.
24. Schoeffel J, Sbeih W, Wallace J. Efficacy of a new endodontic irrigation method using negative pressure. Abstract 1593. Presented at the IADR 83rd General Session; March 9-12, 2005; Baltimore, MD.
25. Mjor IA, Smith MR, Ferrari M, et al. The structure of dentine in the apical region of human teeth. Int Endod J. 2001;34:346-353.

Since completing his endodontic residency and receiving his masters degree at Harvard in 1980, Dr. Schoeffel has been proactive in many endodontic areas. He has maintained a private practice limited to endodontics in Southern California and has lectured globally and frequently on clinical endodontic techniques. As an author of clinically relevant endodontic techniques and methods, his work has been published in both peer-reviewed and other publications. In addition to serving as an endodontic consultant to several companies, he has been awarded 3 United States patents for technologies and methods in the field of endodontics. He can be reached at gjsdds@aol.com.

Disclosure: The author holds 2 United States patents on the EndoVac and receives a royalty from Discus Dental based on sales.