Written by G. John Schoeffel, DDS, MMS Sunday, 30 September 2007 19:00
A recent study by Clegg, et al1 comparing the efficacy of sodium hypochlorite, chlorhexidine, and Bio-Pure (DENTSPLY Tulsa) demonstrated that 6% sodium hypochlorite was the only root canal irrigant that could completely remove biofilm from the root canal system and prevent microbial growth. Despite this finding, fear of a sodium hypochlorite accident (Figures 1 to 3)2 still compels researchers to seek endodontic irrigants comparable to sodium hypochlorite in efficacy but without the risk of tissue destruction beyond the apical foramen.3
Figure 1. Sodium hypochlorite accident following positive pressure irrigation of a maxillary posterior tooth. Note the panfacial vasculature effect. This is not typical of an inadvertent injection of sodium hypochlorite into the maxillary sinus when the patient only reports the taste of “bleach” at the back of the throat.(Mehra P, Clancy C, Wu J. Formation of a facial hematoma during endodontic therapy. J Am Dent Assoc. Jan 2000;131:67-71. Copyright 2000 American Dental Association. All rights reserved. Reprinted by permission.)
Figure 2. Sodium hypochlorite accident in the mandibular region. Note the widespread diffusion of sodium hypochlorite sublingually.
Figure 3. Widespread diffusion of sodium hypochlorite into the soft palate.
|(Figures 2 and 3 were originally featured in the article Review: the use of sodium hypochlorite in endodontics—potential complications and their management [Br Dent J. 2007;202: 555-559], with reprint permission by Stephen Hancocks, OBE, Editor-in-Chief of the British Dental Journal.)|
Although many other irrigants compare favorably with sodium hypochlorite’s antimicrobial characteristics,4 “It is still an open question which of these irrigants is preferable with respect to clinically important properties such as antibacterial activity and tissue dissolution.”5 Ironically, the key to the dilemma was identified, yet not pursued, by Walton and Torabinejad almost 20 years ago. They stated that, “Perhaps the most important factor is the delivery system and not the irrigating solution per se.”6 After reading this reference, this author began developing an irrigation system capable of delivering abundant quantities of sodium hypochlorite to full working length (WL) in conservatively prepared canals and without the danger of extrusion into the periradicular vasculature.
Figure 4. Positive pressure irrigation. Little or no irrigant reaches the apical 2 mm in a closed system. (Illustration courtesy of Discus Dental.)
Figure 5. SEM 2.6 mm from WL. The tubules are consistent for tubular distribution and frequency. By definition these tubules are in the apical third, but they are not in the apical 2 mm.
Figure 6. Less than 1 mm from WL. The area is almost devoid of tubules. The only tubules present in the magnification are irregular and almost nonexistent. This arrangement of tubules is never shown in SEM studies that seemingly prove cleanliness of the most critical portion of the apical third.
Figure 7. Shown above is 0.5 mm from the apical termination. The area has no dentinal tubules because this is cementum—where it belongs—0.5 mm from the apical termination. This area was examined using energy dispersive spectroscopy—virtually no carbon was detected, indicating a surface devoid of organic material.
A literature review revealed a basically ignored paper by Chow7 from 1989, in which he determined that traditional positive pressure irrigation had virtually no effect apical to the orifice of the irrigation needle in a closed root canal system (Figure 4). Fluid exchange and debris displacement were minimal. Equally important to his primary findings, Chow7 set forth an infallible paradigm for endodontic irrigation: “For the solution to be mechanically effective in removing all the particles, it has to: (a) reach the apex; (b) create a current (force); and (c) carry the particles away.”
More recent in vitro studies, using traditional positive pressure irrigation techniques8-10 and scanning electron microscope (SEM) validation, seem to contradict Chow7 by demonstrating excellent irrigation results in the apical third of the root canal. However, SEM validation gives rise to confusion and misinterpretation because dentinal tubular anatomy and distribution differ greatly between the coronal and apical areas of the apical third. Mjor, et al11 demonstrated that (a) “the tubules tended to fade away toward the cementum,” (b) “in the most apical part of the teeth, the tubules were irregularly arranged,” and (c) “no tubules could be discerned in the dentine bordering the cementum in demineralized histological sections.”
Unlike the homogeneous distribution of tubules found coronal to the terminal 2 mm, the apical-most area is almost devoid of tubules, and those present have an irregular distribution (Figures 5 to 7). The left-hand images in Figures 5 to 7 show a longitudinal section of the apical 3 mm of a lower incisor treated with the EndoVac method of ANP under in vivo conditions (sealed apex). The 4 round dots are reference points placed 1 mm apart, and in each figure the “x” on the image marks the area shown on the magnified right-hand SEM image. It can clearly be seen that the number of tubules and their pattern varies depending on the location within the apical third. Accordingly, SEM examinations should not be limited only to those areas rich with tubules coronal to the apical 2 mm; however, in studies they all are, as confirmed by the tubular patterns.
Another technical flaw occurs in in vitro irrigation studies when the examiner fails to seal the apical termination during testing.12 While such studies seem to demonstrate excellent apical debridement and disinfection using positive pressure, the lack of apical seal allows free flow of irrigant through the apical foramen (Figure 8). Most irrigation study designs contain this flaw, ignoring the findings of Chow discussed earlier in this article, and thus resulting in a false representation of the irrigant(s) true action at the apical termination. Under in vivo conditions this extrusion would result in a catastrophic sodium hypochlorite accident. Studies that did/do properly seal the apex during irrigation technique testing have failed to produce favorable results when using traditional positive pressure techniques.13-15
Figure 8. Extrusion of irrigant through the open apical foramen.
Figure 9. Relationship of the maxillary posterior teeth and the maxillary sinus. Due to direct communication between the posterior teeth and the maxillary sinus, little or no irrigation pressure is required to eject endodontic irrigants into the sinus. Endodontic residents have tested the safety of the EndoVac microcannula using this anatomical situation to create a “worst case” safety evaluation.
Figure 10. The EndoVac’s microcannula. The last 0.7 mm is populated with 12 radial holes. These direct the irrigant to full WL while serving as a filter to prevent clogging of the lumen during aspiration. Note: 6 of the holes are located on the underside of the microcannula in this view and therefore are not visible.
Figure 11. ANP using the EndoVac system. The EndoVac microcannula is shown at full WL. It is attached to the office HiVac and creates ANP (vacuum at the apex). As irrigants are added at the access opening they are rapidly “sucked” down and across the canal walls to full WL, then drawn away from the delicate apical tissues via aspiration. (Illustration courtesy of Discus Dental.)
THE SODIUM HYPOCHLORITE ACCIDENT
Fear of the sodium hypochlorite accident touches upon every aspect of endodontic treatment, from patient safety to dreaded years of litigation. What causes this phenomenon? All maxillary posterior teeth are capable of direct communication with the maxillary sinus, and sometimes even the Schneiderian membrane is absent (Figure 9). Direct communication between the maxillary sinus and the root canal systems of these teeth offers virtually no resistance to fluid escaping from the root canal space,16,17 and may be the most frequent cause of a sodium hypochlorite accident. However, these accidents also happen in the mandibular region, sometimes with even more devastating consequences18 (Figures 2 and 3).
Although the exact mechanism for the sodium hypochlorite accident has never been elucidated, the capillary blood pressure in the pulp is about 25-mm Hg or 0.48 psi,19 and the pulpal and periapical capillaries would seem to be a logical portal of entry to the immediate vasculature once endodontic irrigation pressure exceeds the normal regional blood pressure. In 2002, Bradford, et al20 explored several needle factors to determine which could produce the safest air pressure method to dry the root canal system. They explored open-ended versus side-venting needle designs, placement relative to binding point, and size. Although this study used positive air pressure in the root canal, the results apply equally to irrigation fluids, since “Fluid mechanics is the subdiscipline of continuum mechanics that studies fluids, that is, liquids and gases.”21 Bradford, et al20 concluded 2 disturbing facts: first, “No needle design proved safe to use in either round or ovoid canals, regardless of stage of instrumentation.” Second, “The clinical significance of these results is that there is no way to ensure complete safety when drying canals with pressurized air.” Given that the principles of fluid mechanics apply to both gases and liquids, there is also no way to ensure complete safety when delivering canal irrigants under positive pressure. Bradford, et al20 further concluded (again applicable to canal irrigation) that “Vacuum, rather than air under pressure, may be a superior means for canal drying.” The operative word is vacuum.
The EndoVac (endodontic vacuum) was designed to overcome the dangers of pushing irrigants into the capillary beds or the maxillary sinus by creating an apical negative pressure at full WL. The key component of the EndoVac system is a microcannula with an external diameter of 0.32 mm, a spherically sealed end used for guidance, and a population of 12 microholes radially arranged in the last 0.7 mm (Figure 10). The microholes serve 2 functions: to pull endodontic irrigants directly and abundantly to the last 0.2 mm of WL (Figure 11), and to serve as a micro filtration system to prevent clogging of the lumen (internal diameter) of the microcannula.
Other manufacturers also claim endodontic irrigation via “negative pressure,” but not “apical negative pressure.” Apical is the operative word. True ANP only occurs if the needle/cannula is used to aspirate irrigants from the apical termination of the root canal space (Figure 11). If the needle/cannula is used to discharge irrigants into the root canal system (Figure 4), it is a positive pressure device. Two simple metaphors best help describe the differences: the fire hose and the sewer pump. If irrigants are pushed out of the needle/cannula, which is how a fire hose discharges water, this is positive pressure. If the irrigants are sucked into the needle/cannula, which is how a sewer pump cleans a septic tank, this is apical negative pressure.
The apical suction effect of pulling (not pushing) endodontic irrigants down and along the walls of the root canal system creates a rapid turbulent cascading effect as the irrigants are forced to flow between the canal walls and the external surface of the microcannula. This turbulent action creates a current force, while the position of the microholes directs this fast-flowing stream of irrigant as close as 0.2 mm from full WL before reversing the irrigant’s direction up the microcannula. Throughout this procedure the vacuum pressure pulls micro particles out of the root canal system, thus achieving each of Chow’s irrigation objectives.
Finally, Fukumoto22 in Japan as well as Haas and Edson23 at the University of Southern California have studied the safety dynamics of ANP. Fukumoto’s22 protocol employed a root canal space sealed apically with a clear-colored agar. Using 6% sodium hypochlorite, one test group was irrigated using positive pressure and the other using ANP. Escaping sodium hypochlorite created an observable color change in the agar at the apex. She concluded the following: “Root canal irrigation using the intracanal aspiration technique was effective in removing the smear layer in the apical region of modified root canals, without extrusion of the irrigant.”
Haas and Edson23 based their protocol on previous studies that used an unsealed apex with a means to create a balanced apical pressure between the root canal system and the area immediately beyond the apical foramen.24-27 Their study was designed to examine the scenario most likely to produce a sodium hypochlorite accident, specifically a root canal space with no apical resistance to fluid flow, as encountered in the maxillary sinus region (Figure 9). Seven different teeth, each representing a root that could communicate with the maxillary sinus, were mounted in a screw-on cap used to seal a sampling bottle. Three USC endodontic graduate students irrigated each tooth with water under blind conditions, using both the Endo-Vac (ANP) and traditional positive pressure techniques. In the case of the EndoVac technique the micro cannula was placed at exact WL, while for the positive pressure technique the open-ended or side-vented positive pressure needle was placed 2 mm from WL. The sampling jars with the caps and mounted teeth were weighed before and after irrigation. Haas and Edson23 found: “The teeth irrigated with negative apical pressure had no apical leakage. While the teeth irrigated with positive pressure leaked an average of 2.41 mL out of 3 mL.”
This article has presented an overview of the shortcomings encountered with positive pressure intercanal endodontic irrigation: lack of clean canal in the last few millimeters of the root canal system and the omnipresent danger of a sodium hypochlorite accident. Two current studies were cited demonstrating that ANP not only draws an endodontic irrigant to the source of the vacuum pressure, but also prevents any extrusion of the irrigant beyond the apical foramen in both the sealed and open apex situations. The next article will concentrate on recent studies validating the efficacy of the EndoVac system in terms of biological results and to-the-apex organic debris and smear layer removal from the most challenging irregularities of the root canal space.
- 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.
- Mehra P, Clancy C, Wu J. Formation of a facial hematoma during endodontic therapy. J Am Dent Assoc. 2000;131:67-71.
- Effects of irrigation medicaments and techniques. Presented at: American Association of Endodontists 2007 Annual Session; April 25-28; Philadelphia, PA.
- Ferraz CC, Gomes BP, Zaia AA, et al. In vitro assessment of the antimicrobial action and the mechanical ability of chlorhexidine gel as an endodontic irrigant. J Endod. 2001;27:452-455.
- Ercan E, Ozekinci T, Atakul F, et al. Antibacterial activity of 2% chlorhexidine gluconate and 5.25% sodium hypochlorite in infected root canal: in vivo study. J Endod. 2004;30:84-87.
- Walton RE, Torabinejad M. Principles and Practice of Endodontics. Philadelphia, PA: WB Saunders; 1989.
- Chow TW. Mechanical effectiveness of root canal irrigation. J Endod. 1983;9:475-479.
- Torabinejad M, Khademi AA, Babagoli J, et al. A new solution for the removal of the smear layer. J Endod. 2003;29:170-175.
- Khademi A, Yazdizadeh M, Feizianfard M. Determination of the minimum instrumentation size for penetration of irrigants to the apical third of root canal systems. J Endod. 2006;32:417-420.
- 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.
- 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.
- 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.
- Usman N, Baumgartner JC, Marshall JG. Influence of instrument size on root canal debridement. J Endod. 2004;30:110-112.
- 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.
- Albrecht LJ, Baumgartner JC, Marshall JG. Evaluation of apical debris removal using various sizes and tapers of ProFile GT files. J Endod. 2004;30:425-428.
- Hauman CH, Chandler NP, Tong DC. Endodontic implications of the maxillary sinus: a review. Int Endod J. 2002;35:127-141.
- Ehrich DG, Brian JD Jr, Walker WA. Sodium hypochlorite accident: inadvertent injection into the maxillary sinus. J Endod. 1993;19:180-182.
- 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.
- Chien S. Hemodynamics of the dental pulp. J Dent Res. 1985;64:602-606.
- Bradford CE, Eleazer PD, Downs KE, et al. Apical pressures developed by needles for canal irrigation. J Endod. 2002;28:333-335.
- Fluid mechanics. http://en.wikipedia.org/wiki/Fluid_mechanics. Accessed August 28, 2007.
- Fukumoto Y, Kikuchi I, Yoshioka T, et al. An ex vivo evaluation of a new root canal irrigation technique with intracanal aspiration. Int Endod J. 2006;39:93-99.
- 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.
- Lambrianidis T, Tosounidou E, Tzoanopoulou M. The effect of maintaining apical patency on periapical extrusion. J Endod. 2001;27:696-698.
- Tinaz AC, Alacam T, Uzun O, et al. The effect of disruption of apical constriction on periapical extrusion. J Endod. 2005;31:533-535.
- Brown DC, Moore BK, Brown CE Jr, et al. An in vitro study of apical extrusion of sodium hypochlorite during endodontic canal preparation. J Endod. 1995;21:587-591.
- Myers GL, Montgomery S. A comparison of weights of debris extruded apically by conventional filing and Canal Master techniques. J Endod. 1991;17:275-279.
Disclosure: The author holds 2 United States patents on the EndoVac and receives a royalty from Discus Dental based on sales.
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