Dental Tribune United Kingdom Edition

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The higher concentration may also favour superior microbi- al outcomes.41 NaOCl has a broad antimicrobial spectrum,20 includ- ing but not limited to E. faecalis. NaOCl is superior among irrigat- ing agents that dissolve organic matter. EDTA is a chelating agent that aids in smear layer removal and increases dentine permeabil- ity,42,43 which will allow further ir- rigation with NaOCl to penetrate deep into the dentinal tubules.44 General safety precautions Regardless of which irrigant and irrigation system is employed, and particularly if an irrigant with tissue toxicity is used, there are several general precautions that must be followed. A rubber dam must be used and a good seal ob- tained to ensure that no irrigant can spill from the pulp chamber into the oral cavity. If deep caries or a fracture is present adjacent to the rubber dam on the tooth being isolated, a temporary sealing ma- terial must be used prior to per- forming the procedure to ensure a good rubber dam seal. It is also important to protect the patient’s eyes with safety glasses and pro- tect clothing from irrigant splatter or spill. It is very important to note that while NaOCl has unique proper- ties that satisfy most require- ments for a root canal irrigant, it also exhibits tissue toxicity that can result in damage to the adja- cent tissue, including nerve dam- age should NaOCl incidents occur during canal irrigation. Further- more, Salzgeber reported in the 1970s that apical extrusion of an endodontic irrigant routinely oc- curred in vivo.45 This highlights the importance of using devices and techniques that mini- mise or prevent this. NaOCl incidents are discussed later in this article. Irrigant delivery systems Root canal irrigation systems can be divided into two catego- ries: manual agitation techniques and machine-assisted agitation techniques.9 Manual irrigation includes positive-pressure irri- gation, which is commonly per- formed with a syringe and a side- vented needle. Machine-assisted irrigation techniques include son- ics and ultrasonics, as well as newer systems such as the Endo- Vac (SybronEndo), which deliv- ers apical negative-pressure ir- rigation,46 the plastic rotary F File (Plastic Endo),47,48 the Vibringe (Vibringe),49 the Rinsendo (Air Techniques),9 and the EndoActi- vator (DENTSPLY Tulsa Dental 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, par- ticularly to the apical third, and whether the irrigant is capable of debriding areas that could not be reached with mechanical instru- mentation, such as lateral canals and isthmuses. When evaluating irrigation of the apical third, the phenomenon of apical vapour lock should be considered.50–52 Apical vapour lock Since roots are surrounded by the periodontium, and unless the root canal foramen is open, the root canal behaves like a close-ended channel. This produces an apical vapour lock that resists displace- ment during instrumentation and final irrigation, thus preventing the flow of irrigant into the apical region and adequate debridement of the root canal system.53,54 Apical vapour lock also results in gas en- trapment at the apical third.9 Dur- ing irrigation, NaOCl reacts with organic tissue in the root canal system, and the resulting hydroly- sis liberates abundant quantities of ammonia and carbon dioxide.55 This gaseous mixture is trapped in the apical region and quickly forms a column of gas into which further fluid penetra- tion is impossible. Extension of instruments into this vapour lock does not reduce or remove the gas bubble,56 just as it does not enable adequate flow of irrigant. The phenomenon of apical va- pour lock has been confirmed in studies in which roots were em- bedded in a polyvinylsiloxane im- pression material to restrict fluid flow through the apical foramen, simulating a close-ended chan- nel. 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 pres- ence of apical vapour lock.60 In fact, studies conducted without ensuring a close-ended channel cannot be regarded as conclusive on the efficacy of irrigants and the