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roots - international magazine of endodontology No. 1, 2016

irrigation review | 17roots1 2016 Syringe irrigation Irrigation methods are categorised as positive-­ pressureor­negative-pressure,accordingtothemode of delivery employed.4 In positive-pressure techni­ ques, the pressure difference necessary for irrigant flow is created between a pressurised container (e.g. a syringe) and the root canal. In negative-pressure techniques,theirrigantisdeliveredpassivelynearthe canal orifice and a suction tip (negative-pressure) placed deep inside the root canal creates a pressure difference. The irrigant then flows from the orifice towards the apex, where it is evacuated. A detailed ­understanding of the irrigation ­dynamics associated with syringe-based irrigation would aid in improving its effectiveness in clinical practice. Irrigant flow during syringe irrigation The flow of irrigants is influenced by its physical characteristics, such as density and viscosity.5 These properties for the commonly used endodontic irrig- ants are very similar to those of distilled water.6, 7 The surface tension of endodontic irrigants and its de- crease by surfactants have also been studied exten- sively.Therationaleofthiscombinationisthatitmay ­significantly affect (a) the irrigant penetration into dentinal tubules and accessory root canals8, 9 and (b) the dissolution of pulp tissue.10 However, it is impor­ tanttonotethatsurfacetensionwouldonlyinfluence the interface between two immiscible fluids, and not between the irrigant and dentinal fluid.5, 11 Experi- ments have confirmed that surfactants do not en- hance the ability of sodium hypochlorite to dissolve pulptissue12, 13 ortheabilityofchelatingagentstore- move the smear layer.14, 15 The type of needle used has a significant effect on the flow pattern formed within the root canal, while parameterssuchasdepthofneedleinsertionandsize ortaperofthepreparedrootcanalhaveonlyalimited influence.16–19 Generally, the available needles can be classified as closed-ended and open-ended needles. In the case of open-ended needles (flat, bevelled, notched), the irrigant stream is very intense and ex- tends apically along the root canal. Depending upon the root canal geometry and the depth of needle in- sertion, reverse flow of ­irrigant occurs near the canal wall towards the canal orifice. In the case of closed-ended needles (side-vented), thestreamofirrigantisformedneartheapicalsideof theoutletandisdirectedapically.Theirriganttendsto follow a curved route around the needle tip, towards thecoronalorifice.Theflowofirrigantapicaltotheexit oftheneedleisgenerallyobservedtobeapassivefluid flowing zone (dead zone), while the flow of irrigant in the remaining aspect of the root canal is observed to beanactivefluidflowingzone(activezone;Figs.1a–d & 2a–d). A series of vortices of flowing irrigant are generated apical to the tip. The velocity of irrigant inside each vortex decreases towards the apex. Large needles when used within the root canal hardlypenetratebeyondthecoronalhalfoftheroot canal. Currently, smaller-diameter needles (28- or 30-­­gauge) have been recommended for root canal ir- rigation.20, 21 Thisismainlybecauseoftheirabilitytoad- vancefurtheruptotheWL.Thisfacilitatesbetterirrig- antexchangeanddebridement.22–24 Inaddition,theuse of a larger needle would result in decreased space be- ing available for the reverse flow of irrigant between the needle and the canal wall. This scenario has been associated with (a) an ­increased apical pressure for open-endedneedlesand(b)decreased­irrigantrefresh- mentapicaltothetipforclosed-endedneedles.17, 19 The influence of tooth location (mandibular, maxillary) on irrigantflowhasbeenobservedtobeminor.16, 25 Irrigant refreshment Irrigant exchange in the root canal system is a key prerequisite for achieving optimum chemical effect, because the chemical efficacy of the irrigants are known to be rapidly inactivated by dentine, tissue remnantsormicrobes.24, 26, 27 Investigationshaveex- plained the limitations in the irrigant refreshment apical to needles.21, 28–30 Enlarging the root canal to placetheneedletoafewmillimetresfromtheWLand ensuring adequate space around the needle for re- verse flow of the irrigant towards the canal orifice allow effective irrigant refreshment coronal to the Fig.2a Fig.2b

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