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Endo Tribune United Kingdom Edition

22 Endo Tribune United Kingdom Edition | 9/2016 TRENDS & APPLICATIONS Irrigation dynamics in root canal therapy By Anil Kishen, Canada Irrigation dynamics deals with the pattern of irrigant flow, 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 interaction of irrigant with the canal 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 endodontic irrigants within the root canal is called irrigation. The overall objectives of root canal ir- rigation are to inactivate bacterial biofilms, inactivate endotoxins, and dissolve tissue remnants and the smear layer (chemical effects) inthe root canals,aswellas to allow theflowofirrigantentirelythrough the root canal system, in order to detach the biofilm structures and loosen and flush out the debris from the root canals (physical ef- fects).Whilethechemicaleffective- ness will be influenced by the con- centration of the antimicrobial and the duration of action, the physical effectiveness will depend upon the ability of irrigation to generate op- timum 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 It is important to realise that even the most powerful irrig- ant will be of no use if it cannot penetrate the apical portion of the root canal, interact with the root canalwallandexchangefrequently 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 be- tween a pressurised container (e.g. a syringe) and the root canal. In negative-pressure techniques, the irrigant is delivered passively near the canal orifice and a suc- tion tip (negative-pressure) placed deep inside the root canal creates a pressure difference. The irrigant then flows from the orifice to- wards the apex, where it is evac- uated. A detailed understanding of the irrigation dynamics associ- ated with syringe-based irrigation would aid in improving its effec- tiveness 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 are very similar to those of dis- tilled water.6, 7 The surface tension of endodontic irrigants and its de- crease by surfactants have also been studied extensively. The ra- tionale of this combination is that it may significantly affect (a) the irrigant penetration into dentinal tubules and accessory root ca- nals8, 9 and (b) the dissolution of pulp tissue.10 However, it is impor- tant to note that surface tension would only influence the interface between two immiscible fluids, and not between 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 ability of chelating agents to remove the smear layer.14, 15 The type of needle used has a significant effect on the flow pattern formed within the root canal, while parameters such as depth of needle insertion and size or taper of the prepared root canal have only a limited 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 insertion, reverse flow of irrigant occurs near the canal wall towards the canal orifice. In the case of closed-ended needles (side-vented), the stream of irrigant is formed near the api- cal side of the outlet and is di- rected apically. The irrigant tends Figs. 1a–d: Velocity magnitude of irrigation showing the extent of dead zone. With the open-ended needle tip (a), the velocity progressively decreased 1.5mm apical from the tip. With the side-vented needle tip (b), there was a much lower velocity than with the open-ended tip, and it extended only 0.5mm. 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 1a 1b 1c 1d 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 2c 2d

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