Written by G. John Schoeffel, DDS, MMS Thursday, 31 July 2008 19:00
Regardless of the state of a root canal’s decomposition, a successful outcome requires that all organic contents, including the pulp tissue (vital/infected/necrotic), microbiota and their byproducts, and dentinal instrumentation debris, must be physically or chemically removed from the root canal system.1-3 Furthermore, failure to achieve complete debridement and disinfection of the root canal space precludes the possibility of obtaining complete obturation of the canal system at the wall-sealer interface, and regardless of the type of obturation method utilized, this can compromise future success. Total elimination of all the organic components within the root canal space depends on the hydrolysis of amino acids and the saponification of fatty acids by NaOCl (sodium hypochlorite). Accordingly, these reactions must favor chemical equilibrium in the direction of the NaOCl, thereby increasing the velocity of the reaction.4 This can only be achieved by the rapid movement of abundant 5.25% or 6.0% NaOCl through the entire apical region right to the periapical tissue interface—and for the patient’s safety, no further.
As the inventor of the EndoVac system, I have found it difficult to explain the system’s clinical technique because the traditional paradigm of positive pressure root canal irrigation has been deeply ingrained into our thinking since our experiences in Endodontics 101. We were all taught to cautiously inject NaOCl into the root canal space while not binding the injection needle, but we were never taught to deliver NaOCl to the full working length via apical vacuum, as this technique did not exist until 2005. Since the EndoVac endodontic irrigation system operates on physical principles that are different from our customary endodontic paradigm, specifically apical vacuum pressure, understanding this system can be quite confusing.
Figure 1. An in-line sintered glass filter (A), was used to trap all dentinal debris removed from a 4-canaled lower molar during instrumentation and macro irrigation. (Note: 1. Between Phases I, II, and III the filter was removed and cleaned. 2. The organic debris was hydrolyzed via NaOCl, thus not retrievable.) The filter is shown next to a dime for size comparison. The dentinal debris (B) was recovered during orifice opening. Its texture is coarse, and the amount trapped is equivalent in quantity to the debris removed during the balance of instrumentation (C). Finally, very fine dentinal debris is recovered (D) during micro evacuation immediately following all instrumentation. If the debris shown above is not successfully evacuated prior to the commencement of micro evacuation, any of the shown debris could easily clog the holes of the micro cannula shown in Figure 5.
Further adding to this confusion are the physical challenges that must be overcome in order to produce a successful endodontic aspiration system that does not become clogged while working within the limitations of a conservative preparation that is filled with instrumentation debris (Figure 1), as well as the requirement of using the vacuum pressure of an ordinary dental HiVac system. Clogging is not a problem once the clinician understands the EndoVac system components and their interrelationships, hence the purpose of this article. The next article, and last installment in this endodontic series, will describe the clinical use of these components.
UNDERSTANDING THE ENDOVAC SYSTEM’S COMPONENTS
Figure 2. The master delivery tip (A) is attached to a 20-cc syringe. It delivers irrigant from the syringe through the metal cannula into the orifice of the pulp chamber (B). The plastic hood surrounding the delivery tip is attached to the office HiVac and is used to immediately evacuate any excess irrigant (see arrows in B). As shown, the tip is placed just inside the access opening, and irrigant delivery is directed toward an axial wall, not toward or into a root canal. When used concurrently with orifice expansion (Phase I Evacuation), this addition/evacuation action instantaneously evacuates large quantities of dentinal debris (C). After the orifice is opened, the MDT is used at each instrument change (Phase II Evacuation); see Figure 6. It is also used during macro (Figure 3) and micro (Figure 4) evacuation (Phases III and IV) to control and maintain a brim full pulp chamber.
|Figure 3. The macro cannula is made of transparent blue polypropylene and fits into a titanium handpiece for operator convenience (A). It is used in conjunction with the MDT to “pressure wash” the coronal two thirds of the canal system. The clinician places it into the canal as far as possible (B). Then, while the assistant delivers irrigant from the 20-cc syringe at the rate of approximately 15 cc per 20 seconds, the clinician moves the macro cannula quickly up and down from canal orifice to its apical extent. During this macro “pressure wash,” the clinician watches for bubble formation and evacuation thru the polypropylene. If the flow stops, indicating that debris has been caught in the macro cannula, it is removed from the canal, the debris is wiped from the tip, or air from the 3-way syringe is delivered at the back of the handpiece, and macro evacuation resumes. This process ensures virtually complete removal of dentinal debris (C) from the coronal two thirds that could clog the holes of the micro cannula.|
Three different components comprise the EndoVac system: the master delivery tip (MDT; Figure 2), the macro cannula (Figure 3), and the micro cannula (Figure 4). They are used separately (or together) in 4 discrete phases of root canal preparation and final irrigation: access opening, canal preparation, macro irrigation, and micro irrigation.
It is easiest to understand the clinical technique by first explaining the design and use of the cannula used for micro evacuation. The micro cannula (Figure 4A) has an array of 12 micro holes, each measuring 0.10 mm in diameter, and is attached to the office HiVac via a Luer connector. After complete canal instrumentation, it is placed at full-working length, and, as irrigant is added to the pulp chamber, the apical negative pressure draws irrigant apically and across the canal walls (Figure 4B). The flow rate of NaOCl down the root canal is typically 3 mL per minute. This causes rapid organic tissue dissolution and subsequent release of instrumentation debris that is carried to the source of the vacuum—the array of micro holes at the tip. Each micro hole is smaller than the internal diameter of the micro cannula and acts as a filter to prevent internal (nonreversible) clogging. If the clinician follows the correct protocol for all phases of the EndoVac irrigation, less than 10 of the micro holes will become clogged, thus allowing uninterrupted flow of the irrigation solution throughout the EndoVac procedure. However, if the root canal is not properly prepared to receive the micro cannula, all 12 holes will quickly fill with debris (Figure 5), and the clinician will have to remove the micro cannula from the canal and clear it via the 3-way syringe. The correct protocol begins when the first rotary instrument is used in the root canal space or at the orifice expansion.
|Figure 4. The micro cannula (A) measures 0.32 mm in diameter and is made of stainless steel. It has a spherical, welded end for guidance to working length in curved canals and to prevent blockage during either placement or evacuation. It has 12 radially arranged holes, each measuring 0.10 mm in diameter located between 0.2 and 0.7 mm from the spherical weld. These serve as filters to prevent the lumen from clogging during use and to direct the irrigant to full working length (B and C [closeup]). If 3 of the 12 micro holes remain clear, current flow will not be affected.|
PHASE I: ORIFICE OPENING
Referring to Figure 2A, the master delivery tip (MDT) is a specially designed irrigation delivery tip and evacuation hood used to deliver an irrigation solution (normally NaOCl) to the pulp chamber in abundant quantities while concurrently evacuating the excess. The MDT works in any tooth regardless of vertical orientation. The delivery tip extends 2.0 mm past the evacuation hood and is “hooked” on the wall of a posterior tooth or set just inside the access opening when working on an anterior tooth. Its short length is not only necessary to permit use in both anterior and posterior teeth, but also to prevent the clinician or assistant from placing it into the orifice of a root canal. This must never be permitted! The EndoVac process begins immediately after all canals are located and working lengths are confirmed. During the entire root canal preparation process, orifice expansion generates the largest amount of dentinal debris, regardless of type of rotary instrument used. Accordingly, during the orifice-opening phase, the MDT is used concurrently with orifice expansion instruments to apply and evacuate large quantities of NaOCl (Figure 2B). At this point, the assistant delivers the NaOCl directly into the pulp chamber. Figure 2C demonstrates the typical amount of dentinal instrumentation debris evacuated at this point.
(Clinical Note: Prior to initiating use of the MDT the integrity of the clinical crown must be ensured so as not to allow leakage of NaOCl under the rubber dam. This will be expanded upon in Part 4.)
PHASE II: CANAL PREPARATION
|Figure 5. When the micro cannula is placed at full working length (A), and vacuum pressure is present, it draws irrigant from the pulp chamber into the micro holes and then away (B) from the apical termination (efficacy and safety). As previously discussed, if each phase of EndoVac irrigation is not strictly followed, dentinal debris (D) can and will clog the microholes (C). Note: It takes about 15 cases for both the dentist and assistant to become completely familiar with using the EndoVac.|
The quantity and types of irrigation solutions applied to the root canal system during rotary instrumentation varies widely. Some clinicians use only liquid EDTA as a lubricant during rotary instrumentation. Others use a paste form of EDTA combined with urea peroxide injected into the pulp chamber, or applied to the rotary instruments, to act as both a lubricant and effervescent agent in order to flush out instrumentation debris as the urea peroxide reacts with NaOCl.5 Still others use positive pressure needles to inject various concentrations of NaOCl between instruments to flush out instrumentation debris.6 Some clinicians even warm the NaOCl irrigation solution.7
All of the techniques described above are contraindicated during rotary instrumentation. First, 5.25% or 6.0% NaOCl is a lubricant it-self,8 thus requiring no other irrigation solutions during rotary instrumentation, provided that the clinician always works the rotary instruments in a pulp chamber brim-full with NaOCl. Second, when a clinician uses urea peroxide in the root canal, it reacts rapidly with NaOCl, thereby disfavoring the equilibrium reaction of NaOCl, which reduces the tissue solvent effects of the NaOCl. Every clinician has noted the rapid bubbling reaction when NaOCl encounters pulp tissue—nothing should be allowed to alter this effect. Third, due to safety issues, positive-pressure needles should never be used in a root canal to deliver an irrigation solution regardless of depth or stage of instrumentation.9
Figure 6. Immediately after each size of rotary instrument is removed from the root canal(s) and as the next size instrument is inserted into the handpiece, the MDT is used to deliver fresh NaOCl (A) into the pulp chamber. It only requires approximately 1 cc of irrigant to clear the instrumentation debris (B). Although significant debris is removed (C) during instrumentation and MDT evacuation, enough debris remains along the walls (D; right canal) to clog the micro cannula, thus the requirement of macro evacuation.
A frequent question asked about not using positive pressure irrigation needles is this: How does the clinician exchange the irrigation solution in the root canal system if a fresh solution is not injected between each instrument? The answer is the Ar-chimedean principle of fluid displacement. Root canals are never dry upon the initiation of endodontic therapy. They always contain either pulp tissue in the solid or liquid state, and if the pulp chamber is brim-full with NaOCl, as instruments are worked apically, they will displace the contents of the canal coronally. Then, when the instrument is removed coronally, the NaOCl from the pulp chamber will replace the instrument just as the bath water replaced Archimedes upon his exit. Further, the clinician must envision the rotary instrument not only as a dentinal shaving tool, but also as a soft-tissue grinding instrument. This grinding action allows the NaOCl to quickly contact, macerate, and dissolve ever-smaller and smaller pieces of the pulp tissue as rotary instrumentation continues apically.
During canal rotary instrumentation, debris is rapidly lifted coronally (Figure 6A). Between each change of instrument size, the pulp chamber is flushed with approximately 1.0 mL of fresh 5.25% or 6.0% NaOCl (Figure 6B). This constant exchange negates the need for injecting fresh NaOCl down the canal, since fresh NaOCl is dynamically exchanged throughout instrumentation, resulting in significant dissolution of organic debris and flushing of the dentinal de?bris (Figure 6C). Upon completion of rotary preparation, the root canal(s) will be quite clean, but not clean enough to prevent clogging of the micro cannula (Figure 6D).
PHASE III: MACRO IRRIGATION
After completion of all rotary preparations, a micro-hurricane of NaOCl must be created inside the root canal system by using the macro cannula (Figure 3), which creates a pressure-washing effect along the walls of the root canal system. This micro-hurricane lasts for 20 seconds while at least 15 to 20 mL of irrigation solution are added via the MDT. The macro cannula is made of flexible polypropylene, measures 0.55 mm at the tip, and has an internal diameter of 0.35 mm. This design allows for the necessary, rapid exchange of NaOCl above the apical one third and therefore rarely clogs up. However, occasional clogging is to be expected as pieces of tissue not removed from fins and culde-sacs during instrumentation are sucked into the 0.35-mm orifice. The clinician will quickly note this event while observing the current flow (through the transparent polypropylene) come to an immediate stop. When this occurs, the evacuation hood of the MDT (Figure 2A) immediately takes over the evacuation process, preventing an inadvertent spill of irrigation solution outside the pulp chamber. When macro cannula blockage is observed, the clinician simply removes the macro cannula from the root canal, wipes the tissue from the tip with a 2x2 gauze, and continues the macro evacuation process. The first time this event occurs, the clinician will become firmly convinced of the clinical importance of negative-pressure irrigation. (Note: sometimes tissue will become trapped inside the tip of the macro cannula and it cannot be wiped away. In this case, remove the handpiece from the Luer connector and blow the macro cannula clean with a burst of air from the 3-way syringe).
PHASE IV: MICRO IRRIGATION
|Figure 7. Root canal cross-sectioned 1 mm for working length after instrumentation. Note the debris along the walls (black arrows). This debris will react with NaOCl and form micro bubbles of ammonia and carbon dioxide. These micro bubbles will adhere to the debris and prevent rapid dissolution, thus requiring the “up-down” motion during the micro-irrigation cycle.|
After successful evacuation Phases I through III (referring back to Figure 1), the root canal is devoid of gross organic and dentinal debris from the root canal system above the apical one third. However, significant microscopic debris still remains in the apical one third that must be removed via the micro cannula.10 Most of this debris is organic in nature, and it is located in those parts of the root canal system untouched by rotary instruments (Figure 7). This residual organic debris creates the last problem that must be addressed during the micro phase of irrigation. With the micro cannula placed at full working length, and irrigant cascading down the walls, the last of the organic debris begins its hydrolysis, releasing ammonia and carbon dioxide gas. Unfortunately, these microgas bubbles adhere to the walls, micro cannula, and residual tissue. This serves to “insulate” the residual tissue from further contact with the NaOCl solution. In order to eliminate/evacuate these micro-bubbles, it is necessary for the clinician to lift the micro cannula coronally 2 mm every 6 seconds, then return it to the full working length for 6 more seconds. This is done for a total of 30 seconds during the final micro evacuation phase. This exact clinical protocol will be described in the next and last article to be published in Dentistry Today.
To conclude, here is a metaphor between the destruction of an old building and the EndoVac system:
Imagine the implosion of a large building into its basement space. The debris must be completely cleaned up before building a new structure. At first, large cranes move in to remove the huge chunks of concrete and steel debris (EndoVac: Phase I). Next, smaller Bobcats are used to remove an equal amount of the smaller debris (EndoVac: Phase II). Then, hand shovels are used to scoop-up even smaller debris (EndoVac: Phase III). Finally, a vacuum cleaner is used to evacuate the finest particles left behind (EndoVac: Phase IV). This metaphor accurately describes the principles of the EndoVac process.
- Schilder H. Cleaning and shaping the root canal. Dent Clin North Am. 1974;18:269-296.
- Kakehashi S, Stanley HR, Fitzgerald RJ. The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats. Oral Surg Oral Med Oral Pathol. 1965;20:340-349.
- Molander A, Warfvinge J, Reit C, et al. Clinical and radiographic evaluation of one- and two-visit endodontic treatment of asymptomatic necrotic teeth with apical periodontitis: a randomized clinical trial. J Endod. 2007;33:1145-1148.
- Estrela C, Estrela CR, Barbin EL, et al. Mechanism of action of sodium hypochlorite. Braz Dent J. 2002;13:113-117.
- Stewart GG. A scanning electron microscopic study of the cleansing effectiveness of three irrigating modalities on the tubular structure of dentin. J Endod. 1998;24:485-486.
- Zehnder M. Root canal irrigants. J Endod. 2006;32:389-398.
- 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.
- Yguel-Henry S, Vannesson H, von Stebut J. High precision, simulated cutting efficiency measurement of endo-dontic root canal instruments: influence of file configuration and lubrication. J Endod. 1990;16:418-422.
- Bradford CE, Eleazer PD, Downs KE, et al. Apical pressures developed by needles for canal irrigation. J Endod. 2002;28:333-335.
- Nielsen BA, Craig Baumgartner J. Comparison of the EndoVac system to needle irrigation of root canals. J Endod. 2007;33:611-615.
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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