Endo Tribune Asia Pacific Edition

ENDOTRIBUNE The World’s Endodontic Newspaper · Asia Pacific Edition Published in Hong Kong www.dental-tribune.asia Vol. 13, No. 12 By Prof.Anil Kishen,Canada Irrigation dynamics deals with the patternofirrigantflow,penetration, exchange and the forces produced within the root canal space.Current modes of endodontic irrigation in- clude the traditional syringe needle irrigation or physical methods,such as apical negative-pressure irriga- tion or sonic/ultrasonically assisted irrigation.Since the nature of irriga- tion influences the flow of irrigant up to the working length (WL) and interactionofirrigantwiththecanal wall, it is mandatory to understand the irrigation dynamics associated with various irrigation techniques. Endodontic irrigants are liquid antimicrobials used to disinfect microbial biofilms within the root canal. The process of delivery of en- dodontic irrigants within the root canaliscalledirrigation.Theoverall objectives of root canal irrigation are to inactivate bacterial biofilms, inactivateendotoxins,anddissolve tissue remnants and the smear layer (chemical effects) in the root canals,aswellastoallowtheflowof irrigant entirely through the root canalsystem,inordertodetachthe biofilm structures and loosen and flush out the debris from the root canals (physical effects). While the chemical effectiveness will be in- fluenced by the concentration of the antimicrobial and the duration ofaction,thephysicaleffectiveness will depend upon the ability of irrigation to generate optimum streaming forces within the entire root canal system. The final efficiency of endodon- tic disinfection will depend upon both chemical and physical effec- tiveness.1–3 Itisimportanttorealise that even the most powerful irrig- antwillbeofnouseifitcannotpen- etratetheapicalportionoftheroot canal, interact with the root canal wall and exchange frequently within the root canal system.1 Syringe irrigation Irrigation methods are cate- gorised as positive-pressure or negative-pressure, according to the mode of delivery employed.4 In positive-pressure techniques, the pressure difference necessary for irrigant flow is created between a pressurised container (e.g. a sy- ringe) and the root canal. In nega- tive-pressure techniques, the irrig- ant is delivered passively near the canal orifice and a suction tip (neg- ative-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 im- proving its effectiveness in clinical practice. Irrigant flow during syringe irrigation The flow of irrigants is influ- enced by its physical characteris- tics, such as density and viscosity.5 These properties for the com- monly used endodontic irrigants areverysimilartothoseofdistilled water.6, 7 The surface tension of en- dodontic irrigants and its decrease bysurfactantshavealsobeenstud- ied extensively. The rationale of this combination is that it may 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 important to note that surface tension would only in- fluence the interface between two immisciblefluids,andnotbetween the irrigant and dentinal fluid.5, 11 Experiments have confirmed that surfactants do not enhance the ability of sodium hypochlorite to dissolve pulp tissue12, 13 or the abil- ity of chelating agents to remove the smear layer.14, 15 The type of needle used has a sig- nificant effect on the flow pattern formed within the root canal, while parameterssuchasdepthofneedle insertion and size or taper of the preparedrootcanalhaveonlyalim- ited 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 extends apically along the root canal. Depending upon the root canal geometry and the depth of needle insertion, reverse flow of irrigant occurs near the canal wall towards the canal orifice. In the case of closed-ended nee- dles (side-vented), the stream of ir- rigantisformedneartheapicalside of the outlet and is directed api- cally. The irrigant tends to follow a curved route around the needle tip,towardsthecoronalorifice.The flow of irrigant apical to the exit of the needle is generally observed to be a passive fluid flowing zone (dead zone), while the flow of irrig- ant in the remaining aspect of the root canal is observed to be an ac- tivefluidflowingzone(activezone; Figs. 1a–d & 2a–d). A series of vor- tices of flowing irrigant are gener- ated apical to the tip. The velocity of irrigant inside each vortex de- creases towards the apex. Large needles when used within the root canal hardly penetrate be- yond the coronal half of the root canal. Currently, smaller-diameter needles(28-or30-gauge)havebeen recommendedforrootcanalirriga- tion.20, 21 This is mainly because of their ability to advance further up totheWL.Thisfacilitatesbetterirri- gantexchangeanddebridement.22–24 In addition, the use of a larger nee- dlewouldresultindecreasedspace being available for the reverse flow of irrigant between the needle and the canal wall. This scenario has been associated with (a) an increasedapicalpressureforopen- ended needles and (b) decreased irrigant refreshment apical to the tip for closed-ended needles.17, 19 The influence of tooth location (mandibular, maxillary) on irrig- ant flow has been observed to be minor.16, 25 Irrigant refreshment Irrigant exchange in the root canal system is a key prerequisite for achieving optimum chemical effect, because the chemical effi- cacy of the irrigants are known to be rapidly inactivated by dentine, tissue remnants or microbes.24, 26, 27 Investigations have explained the limitations in the irrigant refresh- ment apical to needles.21, 28–30 En- larging the root canal to place the needle to a few millimetres from the WL and ensuring adequate spacearoundtheneedleforreverse flow of the irrigant towards the canalorificealloweffectiveirrigant refreshment coronal to the needle tip.17,19 Furthermore,increasingthe Figs. 1a–d: Velocity magnitude of irrigation showing the extent of dead zone.With the open-ended needle tip (a), the velocity progressivelydecreased1.5mmapicalfrom the tip.With theside-ventedneedle tip(b),therewasamuchlowervelocity thanwith the open-ended tip,and it extended only 0.5 mm.With the apical negative-pressure irrigation (c),there was a constant velocity slightly higher than the side-vented needle irrigation that was constant as the irrigant moved coronally. The ultrasonically assisted irrigation (d) showed the highest magnitude of velocity,constant to at least 3 mm coronal to the tip placement.35 Irrigationdynamicsinrootcanaltherapy 1a 1b 1c 1d 2c 2d Figs.2a–d:Time-averaged distribution of shear stress on the root canal wall showing a more uniform distribution on the canal wall with the open-ended needle tip (a).The side-vented needle tip (b) showed a localised region with a high amount of shear stress, while there was not an observable level with the EndoVac irrigation (Kerr; c). The ultrasonically assisted irrigation (d) displayed the highest levels of shear stress over the greatest area of the canal wall.35 2a 2b

Endo Tribune Asia Pacific Edition

Pages Overview