Overwhelming evidence supported by countless studies indicate that the best way to ensure success in a root canal procedure is to eliminate microorganisms from the canal system. They are, after all, the primary cause of apical periodontitis, a disease that typically sends patients to the endodontist’s office. The conundrum is that experts have claimed that thorough disinfection is nigh impossible. Thankfully, despite this challenge, modern materials and techniques allow clinicians to achieve predicatable results when performing root canal therapy (RCT).
In this third installment of our root canal series, we explore the crucial step of disinfecting canals — and how sales pros can help clinicians ensure successful long-term outcomes through a better understanding of available resources.
Of course, before canals can be sterilized, they must be shaped and cleaned (see “Tunnel Vision,” October 2012). Employing chemomechanical techniques via antibacterial irrigants, files and other instruments, clinicians remove infected tissue, shaping and cleaning the canal for subsequent obturation (or filling). Once this is completed, canals are soaked and/or flushed with solutions — often the same ones used in the cleaning process. In fact, many practitioners speak of cleaning and disinfecting as one process.
The targets of disinfection include numerous species of bacteria and fungi, which can be found in canals suffering from primary infections, as well as those needing retreatment. Among the usual suspects are Peptostreptococcus spp, Staphylococcus salivaris, Lactobacillus spp, Canidida albicans, Escherichial coli and Enterococcus faecalis.1 The last of these, due to its tenacity, appears to be particularly annoying in primary infections. But getting rid of such a nasty cocktail isn’t exactly a day at the beach.
TERMS TO LEARN
These microorganisms can be found in necrotic tissue and the smear layer, and they even get into dentinal tubules — which can be particularly difficult to access. And because the root canal system is often a maze of lateral canals, fins and isthmuses — inaccessible to conventional cleaning methods — the impossibility of complete, three-dimensional disinfection is well documented. In addition, the very act of instrumentation may cause problems, as resulting debris starts compacting into tubules and smaller tributaries, blocking access to cleaning and disinfecting irrigants.
But despite such obstacles, there is general agreement that RCT is still a successful treatment option. One estimate puts the success rate as high as 98% for teeth without apical periodontitis, and up to 86% for teeth with this disease, with their chance to be functional over time estimated at 91% to 97%.2 So how is this accomplished if thorough disinfection can’t be guaranteed?.
The creation of a clean and well-shaped canal goes a long way toward facilitating disinfection, especially when it comes to tangling with, well, tangled root systems. Not only does this process allow for more thorough final rinses with antibacterial irrigants, but it also paves the way for a tight seal upon obturation. And while adequate sealing prevents reinfection, it serves another purpose, as well.
According to Lisa Germain, DDS, MScD, who operates an endodontic practice in New Orleans, “The reason for the seal is to ‘entomb’ the primary pathogens that are left behind in both the main canal and in accessory canals. Of course, this is not effective unless the canal is disinfected to the best of our ability. That is why root canal success is dependent on cleaning, shaping and sealing the root canal system.”
By entombing bacteria, clinicians hope to kill microorganisms through deprivation of oxygen and nutrients — or at least render them harmless.
Once the shaping and cleaning processes are completed, the focus turns to irrigants to disinfect the canal in a final rinse. Endodontic irrigants are expected to play several roles throughout RCT. Ideally, they must lubricate the canal to expedite instrumentation; dissolve necrotic tissue and other pulpal debris; flush debris out of the canal; kill intracanal bacteria and other microorganisms; and disintegrate the smear layer. Unfortunately, none can really complete all of these tasks; as a result, current thinking favors using several formulations in concert with one another.
The odds-on favorite combo is sodium hypochlorite (NaOCI) and ethylenediaminetetraacetic acid (EDTA). A chelating agent, EDTA cannot disinfect organic tissue because it lacks antibacterial characteristics — but it removes smear layer like a hot knife through butter. A widely held opinion is that the obliteration of smear layer not only enhances sealing ability, but also enhances the disinfection process overall when EDTA is partnered with NaOCI (which is basically household bleach).
While lacking the ability to remove smear layer, NaOCI offers powerful antimicrobial properties, and it can help dissolve necrotic tissue. Paired with EDTA, it would seem to be a match made in heaven, right? Well, most of the time. But, besides its strong smell, less-than-delightful taste, and the fact that it can discolor clothing, NaOCI can lead to serious complications — including nerve damage and worse — if it is accidentally extruded into the periapical area or adjacent areas. Known as an NaOCI “incident,” this is a rare occurrence, fortunately. But because of this and its other faults, there has been a continual quest to find alternatives to NaOCI.3 To date, however, nothing has matched its efficacy.
POINT of SALE
For endodontic success, the bacterial load in root canals must be reduced as much as possible, if not completely. Today’s technology can help reduce endodontic failures stemming from bacteria left in inadequately sealed canals.
MIX IT UP
Aside from replacing NaOCI, there appears to be a trend to add other solutions to the mix. “These two mainstays of endodontic irrigation can be supplemented with other disinfectants, such as chlorhexidine, to enhance the bactericidal actions needed to truly disinfect canals,” asserts Robert Roda, DDS, MS, who practices in Scottsdale, Ariz., and serves as vice president of the American Association of Endodontists.
In vitro studies have shown that chlorhexidine (CHX), which enjoys popularity as a biocide in a range of antiseptics, provides antibacterial effects against E. faecalis that are superior to NaOCI. It lacks the ability to dissolve tissue, however, and further in vivo studies are warranted3 because it has been shown that CHX’s antibacterial effects diminish in the presence of dentin.4?
Other irrigants used for disinfection include hydrogen peroxide (H2O2), iodine, saline and distilled water and citric acid. Even traditional Chinese herbs, such as berberine, have been found to have excellent disinfection qualities.5 All these substances demonstrate varying degrees of efficacy, but none quite manage the overall effectiveness of NaOCI as a disinfectant in the root canal milieu.
There’s also a relative newcomer to the endo irrigant field. Known as MTAD, it is a mix of a tetracycline isomer, citric acid and a detergent called Tween 80. This solution is said to be capable of both removing the smear layer and disinfection, and some researchers claim it may be a viable alternative to the NaOCI/EDTA approach. Others hold that it is best used in conjunction with NaOCI (as an alternative to EDTA), as it is less corrosive to dentin. In fact, one group of researchers advocate using it as a final rinse after applying NaOCI.6
Other entries to the market include those with combined properties. Some feature the addition of detergents to EDTA and NaOCI to enhance smear-layer removal and tissue penetration. Nonetheless, when NaOCI has been compared to combination agents, including MTAD, it is still usually found to be more effective in eradicating bacteria such as E. faecalis.7
TRIED AND TRUE
Stephen Cohen, MA, DDS, FICD, who operates an endodontic practice in San Francisco, reports, “NaOCl is still generally recommended because it is the only liquid that can dissolve organic debris, including bacteria and fungi.” Cohen, who is also an adjunct clinical professor of endodontics at the University of Califonia San Francisco School of Dentistry, adds that solution agitation with sonic and ultrasonic devices is somewhat helpful, though less effective in the apical third of the root canal.
But Germain notes that RCT success hinges on the ability to saturate the apical third with NaOCI. “It is important,” she says, “to make sure that the canal system is not just debrided, but ‘soaked’ with the solution for a period of time. Using a crown-down technique will expedite this process.”
Roda adds, however, “Many systems are now available to agitate irrigants, forcing them into all of the canal’s anatomic complexities to ensure optimal cleaning and disinfection — and in less time than passive soaking requires.”
The conventional method of irrigant delivery has long been accomplished via the application of positive pressure through a syringe with a side-vented needle, coupled with manual agitation via brushes, files or gutta-percha points. New techniques have also been developed to enhance irrigation efficacy. These include rotary instrumentation, the use of brushes and constant irrigation — but it goes much further.
“Irrigating solutions can be agitated using sonic and ultrasonic energy applied to instruments that are inserted in the canal,” Roda reports. “The instruments, which are made of metal or plastic, vibrate at very high rates of speed to move the irrigant around in the canal.”
When ultrasonics are used only for irrigation and not instrumentation, it is called “passive ultrasonic irrigation.” This involves placing an ultrasonically activated noncutting wire or file into a canal already filled with liquid, and allowing it to freely oscillate. The activated tip generates powerful acoustic streaming, which basically means that the irrigant gets circulated into areas it would not otherwise reach, thus helping to remove debris. This technique also results in cavitation, or the formation of thousands of tiny bubbles that produce shock waves when they implode.8
Lasers are also being used in the quest for bacteria-free canals. Photoninitiated photoacoustic streaming using an erbium yttrium aluminum garnet (Er:YAG) laser has demonstrated the ability to remove smear layer using a shockwave effect. It is essentially a cone-shaped fiber tip that’s attached to a handpiece. Using low-energy settings, it’s able to agitate irrigant to remove debris all the way down to the apex, without worry of thermal effects in the canal
Photoactivated disinfection is another laser-based method that’s said to be effective against all sorts of microorganisms. This utilizes a photosensitizer solution that selectively targets bacteria, while not effecting healthy tissue. When the solution is hit with a low-power diode laser, oxygen-releasing dyes are activated that are lethal to bacteria. Says Cohen, “Photoactivated disinfection holds much promise, but further evidence is needed.”
For others, another laser technology is more enticing. Photodynamic therapy involves the use of lowpower lasers that emit a wavelength designed to kill microorganisms that have been subjected to a photosensitizer drug. When irradiated with a specific wavelength of light, the drug is excited. This results in the production of free radicals, which react with oxygen to produce a highly reactive oxygen, ultimately leading to the destruction of microorganisms.
KNOW YOUR ACRONYMS
|We love our acronyms, and the field of endodontics has no shortage of them. Here, at a glance, are some you should know when dealing with this market:
NO PRESSURE, DOCTOR
A negative-pressure device that’s currently on the market is receiving favorable reviews for its ability to safely deliver effective debridement compared to traditional needle irrigation.9 The vacuum-like device pulls irrigant downward rather than injecting it. According to Roda, “Using negative pressure (or vacuum) systems can be effective in not only agitating the irrigating solution, but also in preventing it from being extruded out the end of the tooth into the tissues surrounding the root.”
Though there seems to be a never-ending supply of new techniques and irrigation delivery methods directed at root canal disinfection, the jury is still out on their success. Those with whom we spoke agree that for many of these devices, more studies — both in vitro and in vivo — are needed. “These all still fall short of the ultimate goal, which is complete disinfection of the root canal space,” states Germain. “As long as this is still a problem, new methods to accomplish this goal will continue to be developed.”
Many of the automated methods used in irrigation — and, indeed, the irrigants themselves — are still being researched, and opinions proliferate. Recommendations for their use seem to lean toward applying them in conjunction with other, more conventional methods. But sales pros can rest assured that the innovations will not stop coming as the quest for disinfection through liquid assets continues.
BONUS WEB CONTENT : THE VALUE OF SHAPING IN DISINFECTION
|The shaping process is a vital piece of the puzzle when it comes to canal disinfection, as a well-shaped canal facilitates antibacterial irrigant flow. This is a task accomplished either manually or via rotary instruments. “Hand instrumentation and passive soaking with sodium hypochlorite can be very effective in the hands of an experienced practitioner, but this is a slow process and hard to master,” notes Robert Roda, DDS, MS, an endodontist practicing in Scottsdale, Ariz.
Roda, who also serves as vice president of the American Association of Endodontists, notes that the process has been greatly simplified and enhanced with the advent of newer, engine-driven instrumentation techniques and irrigation technologies. These developments allow better cleaning and disinfection of canals in less time — and with fewer procedural complications — than earlier methods. “Today,” he explains, “canals are instrumented mostly by rotary or reciprocation-type instruments to achieve a well-shaped canal that is ready to be disinfected.”
There is general agreement that flexible hand and rotary NiTi files have been a boon to the shaping process. “With the newer rotary or reciprocal instruments made of NiTi, it is much easier to create the desired continuously tapering funnel shape, even around curvatures in the canal,” reports Roda. “This allows the practitioner to achieve more predictability in canal shaping with a much lower incidence of shaping complications. Coupled with irrigation, it also yields a much better chance of achieving our goals of complete cleaning and disinfection.”
BONUS WEB CONTENT : ENDO DREAMS
|We asked Roda what his dream system would be. “Most of the irrigation agitation systems on the market,” he says, “will clean the canals efficiently, but there is a small risk of extruding the irrigating solution into the tissues surrounding the root end.” While this is infrequent, when it happens, one of two things may occur. “If it is a small amount of irrigant, then there may be a higher incidence of post-operative pain,” he explains. “If a large amount of irrigating solution gets extruded beyond the root end, then the patient can suffer a serious complication that can cause larger problems than treatment failure.”
Because of this, Roda says that clinicians are extremely careful to avoid irrigating to the full length of the canal. Unfortunately, this results in some areas not being thoroughly cleaned.
“The negative pressure (vacuum) methodology prevents problems with extrusion, but it does not agitate the solution well enough to clean in the side branches and other anatomic irregularities in the canal system,” Roda says. “In my opinion, a system that combines the safety of vacuum systems with the agitation of ultrasonics or sonics could give us the best of both worlds.”
Aside from delivery devices, in Roda’s opinion, future emphasis should be placed on altering the irrigating solutions. “Novel delivery systems for our canal disinfectants will continue to arrive,” he predicts, “but we need to change the irrigating solutions themselves. As it stands now, we achieve a high level of disinfection using solutions that kill bacteria well, but are generally toxic to some degree. It is a testament to the training and skill that clinicians have that we can achieve these goals with very few complications.
“In the future, newer irrigating solutions that are nontoxic and less irritating than the ones we have now will be introduced. They will kill microbes, eliminate biofilms and dissolve dead tissue, and yet will not cause complication if overextended beyond the root end. With less toxicity comes the promise of creating an environment in the canal that will allow us to fill it with the best filling material of all: living pulp tissue generated from the stem cells surrounding the root end. When this happens, it will be a large step toward achieving endodontists’ ultimate goal of regenerating the living tooth by achieving complete disinfection with absolute safety.”
- Gajan EB, Aghazadeh M, Abashov R, Salem Milani A, Moosavi Z. Microbial Flora of Root Canals of Pulpally infected Teeth: Enterococcus faecalis a Prevalent Species. J Dent Res Dent Clin Dent Prospects. 2009;3:24–27.
- Friedman S, Mor C. The success of endodontic therapy — healing and functionality. J Calif Dent Assoc. 2004;32:493–503.
- Haapasalo M, Endal U, Zandi H, Coil JM. Eradication of endodontic infection by instrumentation and irrigation solutions. Endod Topics. 2005;10:77–102.
- Haapasalo HK, Siren EK, Waltimo TM, Ørstavik D, Haapasalo MP. Inactivation of local root canal medicaments by dentine: an in vitro study. Int Endod J. 2000;33:126–131.
- Su RY. The effect of berberine in sterilizing infective root canal of deciduous teeth. Zhonghua Kou Qiang Yi Xue Za Zhi. 1992;27:302–305,319.
- Torabinejad M, Cho Y, Khademi AA, Bakland LK, Shabahang S. The effect of various concentrations of sodium hypochlorite on the ability of MTAD to remove the smear layer. J Endod. 2003;29:233–239.
- Dunavant TR, Regan JD, Glickman GN, Solomon ES, Honeyman AL. Comparative evaluation of endodontic irrigants against Enterococcus faecalis biofilms. J Endod. 2006;32:527–531.
- Glassman G, Kratchman S. Ultrasonics in endodontics: luxury or necessity? Dent Today. 2011;114:116–119.
- Nielsen BA, Craig Baumgartner J. Comparison of the EndoVac system to needle irrigation of root canals. J Endod. 2007;33:611–615.