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Dental Tribune Middle East & Africa Edition | September-October 2015 11mcme < Page 10 Techniques),9 and the EndoAc- tivator (DENTSPLY Tulsa Den- tal Specialties).9 Two important factors that should be considered during the process of irrigation are whether the irrigation system can deliver the irrigant to the whole extent of the root-canal system, particularly to the api- cal third, and whether the ir- rigant is capable of debriding areas that could not be reached with mechanical instrumenta- tion, such as lateral canals and isthmuses. When evaluating ir- rigation of the apical third, the phenomenon of apical vapor lock should be considered.50–52 Apical vapor lock Because roots are surrounded by the periodontium, and un- less the root-canal foramen is open, the root canal behaves like a closed-ended channel. This produces an apical vapor lock that resists displacement during instrumentation and final irrigation, thus prevent- ing the flow of irrigant into the apical region and adequate de- bridement of the root-canal sys- tem.53,54 Apical vapor lock also results in gas entrapment at the apical third.9 During irrigation, NaOCl reacts with organic tissue in the root-canal system, and the resulting hydrolysis liberates abundant quantities of ammo- nia and carbon dioxide.55 This gaseous mixture is trapped in the apical region and quickly forms a column of gas into which further fluid penetration is impossible. Extension of in- struments into this vapor lock does not reduce or remove the gas bubble,56 just as it does not enable adequate flow of irri- gant. The phenomenon of apical va- por lock has been confirmed in studies in which roots were em- bedded in a polyvinylsiloxane impression material to restrict fluid flow through the apical foramen, simulating a closed- ended channel. The result in these studies was incomplete debridement of the apical part of the canal walls with the use of a positive-pressure syringe delivery technique.57–60 Micro-CT scanning and histo- logical tests conducted by Tay et al. have also confirmed the presence of apical vapor lock.60 In fact, studies conducted with- out ensuring a closed-ended channel cannot be regarded as conclusive on the efficacy of irrigants and the irrigant system.61–63 The apical vapor lock may also explain why in a number of studies investigators were unable to demonstrate a clean apical third in sealed root canals.59, 64–66 In a paper published in 1983 based on research, Chow deter- mined that traditional positive- pressure irrigation had virtually no effect apical to the orifice of the irrigation needle in a closed root-canal system.67 Fluid ex- change and debris displace- ment were minimal. Equally important to his primary find- ings, Chow set forth an infal- lible paradigm for endodontic irrigation: “For the solution to be mechanically effective in re- moving all the particles, it has to: (a) reach the apex; (b) create a current (force); and (c) carry the particles away.”67 The api- cal vapor lock and considera- tion for the patient’s safety have always prevented the thorough cleaning of the apical 3 mm. It is critically important to deter- mine which irrigation system will effectively irrigate the api- cal third, as well as isthmuses and lateral canals,16 and in a safe manner that prevents the extrusion of irrigant. Manual agitation techniques By far the most common and conventional set of irrigation techniques, manual irriga- tion involves dispensing of an irrigant into a canal through needles/cannulae of variable gauges, either passively or with agitation by moving the needle up and down the canal space without binding it on the canal walls. This allows good control of needle depth and the vol- ume of irrigant that is flushed through the canal.9,63 However, the closer the needle tip is po- sitioned to the apical tissue, the greater the chance of apical ex- trusion of the irrigant.67, 68 This must be avoided; were NaOCl to extrude past the apex, a cata- strophic accident could occur.69 Manual-dynamic irrigation Manual-dynamic irrigation involves gently moving a well- fitting gutta-percha master cone up and down in short 2- to 3-mm strokes within an instru- mented canal, thereby produc- ing a hydrodynamic effect and significant irrigant exchange.70 Recent studies have shown that this irrigation technique is sig- nificantly more effective than automated-dynamic irrigation and static irrigation.9,71,72 Machine-assisted agitation systems Sonic irrigation Sonicactivationhasbeenshown to be an effective method for disinfecting root canals, operat- ing at frequencies of 1–6kHz.73, 74 There are several sonic irriga- tion devices on the market. The Vibringe allows delivery and sonic activation of the irrigat- ing solution in one step. It em- ploys a two-piece syringe with a rechargeable battery. The ir- rigant is sonically activated, as is the needle that attaches to the syringe. The EndoActivator is a more recently introduced sonically driven canal irrigation system.9,75 It consists of a port- able handpiece and three types of disposable polymer tips of different sizes. The EndoActiva- tor has been reported to effec- tively clean debris from lateral canals, remove the smear layer and dislodge clumps of biofilm within the curved canals of mo- lar teeth.9 Ultrasonics Ultrasonic energy produces higher frequencies than sonic energy but low amplitudes, os- cillating at frequencies of 25–30 kHz.9,76 Two types of ultrasonic irrigation are available. The first type is simultaneous ultra- sonic instrumentation and ir- rigation, and the second type is referred to as passive ultrasonic irrigation operating without si- multaneous irrigation (PUI). The literature indicates that it is more advantageous to apply ultrasonics after completion of canal preparation rather than as an alternative to conven- tional instrumentation.9,20,77 PUI irrigation allows energy to be transmitted from an oscillating file or smooth wire to the irri- gant in the root canal by means of ultrasonic waves.9 There is consensus that PUI is more ef- fective than syringe needle ir- rigation at removing pulpal tissue remnants and dentine debris.78–80 This may be due to the much higher velocity and volume of irrigant flow that are created in the canal dur- ing ultrasonic irrigation.9,81 PUI has been shown to remove the smear layer; there is a large body of evidence with different concentrations of NaOCl.9,80–84 In addition, numerous inves- tigations have demonstrated that the use of PUI after hand or rotary instrumentation re- sults in a significant reduction in the number of bacteria,9,85–87 or achieves significantly better results than syringe needle ir- rigation.9,84,88,89 Studies have demonstrated that effective delivery of irrigants to the apical third can be en- hanced by using ultrasonic and sonic devices that demonstrate acoustic micro-streaming and cavitation.79,81,90,91 Acoustic mi- cro-streaming is defined as the movement of fluids along cell membranes, which occurs as a result of the ultrasound en- ergy creating mechanical pres- sure changes within the tissue. Cavitation is defined as the for- mation and collapse of gas and vapor-filled bubbles or cavities in a fluid. The Apical Vapor Lock theory, proven in vitro by Tay, has been clinically demonstrated92 to also include the middle third by Vera: “The mixture of gases is originally trapped in the api- cal third, but then it might grow quickly by the nucleation of the smaller bubbles, forming a gas column that might not only im- pede penetration of the irrigant into the apical third but also push it coronally after it has been delivered into the canal.” However, more recently Mu- noz93 demonstrated that both passive ultrasonic irrigation (PUI) and EndoVac are more effective than the conventional endodontic needle in delivering irrigant to WL of root canals.” This raises the efficacy ques- tion. Two recently published studies examined this issue with both systems by testing their ability to eliminate micro- organisms during clinical treat- ment from infected root canal systems.94,95 Paiva fund that af- ter a supplementary irrigation procedure using PUI with NaO- Cl that 23 percent of the sam- ples produced positive cultures. Cohenca’s study examining the clinical efficacy of the EndoVac fund no microbial growth ei- ther after post instrumentation irrigation or at the one92 week obturation appointment. When questioning these di- verse results, one must remem- ber that microbial hydrolysis via NaOCl is an equilibrium re- action. Hand demonstrated that a 50 percent reduction of NaOCl concentration resulted in a 300 percent reduction in dissolution activity. Accordingly, one must consider both the delivery of the irrigant to full working length, via PUI or apical negative pressure and the total volume of NaOCl exchanged. The volume of an instrumented root canal 19 mm long shaped to a #35 with a 6 percent instrument equals 0.014 cc. Paiva described place- ment of NaOCl via a NaviTip (Ultradent) at WL — 4 mm during instrumentation and discussed using PUI with #15 K file at WL — 1 mm. Prior to PUI, 2 ml of NaOCl was injected into the canal; however, this could not have filled the apical 4 mm95 due to the apical vapor lock. According to Munoz, the canal was most likely immedi- ately filled with ultrasonically activated NaOCl for one min- ute,92 but as just described — only about 0.014 cc would have been effectively available for this exchange and activation. In contrast, the Apical Negative Pressure protocol described by Cohenca et al. approximately 2 ml of NaOCl actively passes through the complete WL for one92 minute.96 The difference in volumetric exchange equals 2/0.014 = 14, 200 percent and likely explains the disinfection differential. The plastic rotary F File Although sonic or ultrasonic in- strumentation is more effective at removing residual canal de- bris than rotary endodontic files are,104 and irrigation solutions are often unable to remove this during endodontic treatment, many clinicians still do not in- corporate it into their endodon- tic instrument armamentarium. The common reasons given for not using sonic or ultrasonic filing are that it can be time- consuming to set up, an unwill- ingness to incur the cost of the equipment, and lack of aware- ness of the benefits of this final instrumentation step in endo- dontic treatment. It is for these reasons that an en- dodontic polymer-based rotary finishing file was developed. This new, single-use, plastic rotary file has a unique file de- sign with a diamond abrasive embedded into a non-toxic polymer. The F File will remove dentinal wall debris and agitate the NaOCl without enlarging the canal further. Pressure-alternation devices Rinsendo irrigates the canal by using pressure-suction tech- nology. Its components are a handpiece, a cannula with a 7 mm exit aperture, and a syringe carrying irrigant. The hand- piece is powered by a dental air compressor and has an irriga- tion speed of 6.2 ml per minute. Research has shown that it has promising results in cleaning the root-canal system, but more research is required to provide scientific evidence of its effi- cacy. Periapical extrusion of ir- rigant has been reported with this device.101, 102 The EndoVac apical negative- pressure system The EndoVac apical negative- pressure irrigation system has three components: the Master Delivery Tip, MacroCannula and MicroCannula. The Master Delivery Tip simultaneously de- livers and evacuates the irrigant (Fig. 2). The MacroCannula is used to suction irrigant from the chamber to the coronal and middle segments of the canal. The MacroCannula or Micro- Cannula is connected via tub- ing to the high-speed suction of a dental unit. The Master Deliv- ery Tip is connected to a syringe of irrigant and the evacuation hood is connected via tubing to the high-speed suction of a dental unit.56 The plastic Mac- roCannula has an open end of ISO size 0.55 mm in diameter > Page 12 Figs. 1a,b: Root-canal complex. (Images/Dr Ronald Ordinala Zapata, Brazil, www.facebook.com/TheInternalAnatomy OfTheHumanTeeth)