The objective of this article is to review the various parameters which make it possible to optimize the action and the efficiency of irrigation in endodontics, and to recall the general recommendations.In the treatment of infection of endodontic origin, the principle for obtaining favorable results is based on the identification of the problem and the elimination of the etiological factors.Bacteria have long been identified as the main etiological factors in the development of pulpal and peri-apical lesions.Thus, the success of endodontic treatment depends on a complete chemo-mechanical debridement of the root canal system allowing the elimination of pulp and dentin debris as well as intra-canal bacteria.Finally, a three-dimensional obturation helps prevent reinfection and promote healing of the surrounding tissues.The complexity of endodontic anatomy represented by the presence of inaccessible areas such as anastomoses, apical ramifications, and isthmuses make the action of instruments insufficient.Several studies have shown that more than 35% of canal surfaces remain uninstrumented (Peters OA 2003) (Fig.1).The importance of the irrigation phase in endodontics is better understood.The role of the mechanical preparation is to create a widening of the canal allowing the irrigation solutions to circulate and to facilitate their penetration into the non-instrumented areas.Fig.1: Prepared canal areas shown in green.A large part of the root canal system is not affected by the instruments during shaping (areas in red).To date, complete sterilization of the canal network is not possible (Senia 1971).The objective of this article is to review the various parameters which make it possible to optimize the action and the efficiency of irrigation in endodontics, and to recall the general recommendations.The ideal irrigation solution must act by:1 – a physical/mechanical action having:Several solutions have been proposed to clean and disinfect the canal system, in particular, sodium hypochlorite, Ethyl Diamino Tetaraacetic acid (EDTA), and chlorhexidine digluconate.Sodium hypochlorite (NaOCl) remains the most commonly used solution in endodontics.This is the solution that best fulfills the expected specifications.This is attributed to its broad-spectrum antibacterial ability and ability to dissolve organic compounds.The main drawbacks of sodium hypochlorite are its cytotoxicity when extruded into the periapical area and its lack of ability to remove smear on its own.In the presence of water, NaOCl is dissociated into hypochlorous acid according to the following equation:NaOCl + H20 -> NaOH + HOCl (hypochlorous acid)In basic medium, the latter dissociates into hypochlorite ion (OCl-):HOCl -> H+ + OCl- (hypochlorite ion)The two forms HOCl and OCl- are in equilibrium and determine the concentration of the product which is expressed as “active chlorine” or “available chlorine”.These two forms are responsible for the antimicrobial and solvent effects of the solution.Sodium hypochlorite is used at concentrations between 0.5% to 5.25%.These concentrations are obtained either from a dilution of the basic solution, or by the use of so-called stabilized solutions.The rotating instrumentation used during shaping creates a dentinal sludge or “smear layer”.The latter consists of an organic component and another mineral.Sodium hypochlorite is only active on the organic component of the smear layer.The use of a demineralizing solution such as EDTA is therefore recommended.EDTA does not have an antiseptic action, nor a solvent action on materials...organic.The combination of EDTA and sodium hypochlorite is therefore the most effective and the most widely used in endodontics.NaOCl removes the organic content of the smear and EDTA dissolves the mineral part.EDTA comes in gel or liquid form at a concentration of 17% and at physiological pH.It is used during the final phase of irrigation for one minute in the liquid form.EDTA induces significant demineralization and alters the structure of the dentin, so prolonged exposure to the tissue should be avoided, it is then eliminated by abundant rinsing with NaOCl.The final effectiveness of endodontic disinfection is based on the mechanical action of irrigation solutions (washing effect), on its ability to destroy bacteria (antiseptic power) and on its solvent action.Mechanical efficiency depends on the ability of irrigation to generate runoff forces throughout the canal system.The chemical effectiveness depends on the concentration, temperature, pH, contact time between the solution and the substrate as well as the interaction with different chemicals.Mechanical effects can be produced even by inert irrigants (e.g. water, saline), but chemical effects are exerted only by chemically active solutions (e.g. sodium hypochlorite).Most publications on endodontic irrigation focus on the chemical action of the solution and the factors that optimize it (especially concentration).It is essential to note that even the strongest solution can only be effective if it can penetrate deep into the channel and come into direct contact with the substrate to be removed.In 1982, Moorer and Wesselink concluded that: "Although any concentration of sodium hypochlorite between 0.3% and 5% can be used successfully in endodontics, it seems that the mechanical aspects of the technique are more important than the initial concentration of sodium hypochlorite.With better shaping technique combined with more frequent changes of sodium hypochlorite, a lower concentration of the solution can be used for sufficient trimming and disinfection of the root canal system.”So we understand better that the mechanical aspect of the irrigation seems as important as the antibacterial characteristics of the solutions.In endodontics, the choice of the concentration of sodium hypochlorite is still the subject of much debate.The most commonly used concentrations vary between 0.5% and 5.25%.At low concentration (<1%), sodium hypochlorite retains its antiseptic properties but loses its solvent power on the pulp tissues.At a concentration greater than or equal to 5%, sodium hypochlorite has a greater antiseptic action (Gomes et al 2001), and a very powerful solvent power.Nevertheless, at a high concentration, sodium hypochlorite exhibits a significant cytotoxic effect in the event of accidental injection into the periapex.Today, a concentration of 2.5% – 3% seems a good compromise.In endodontics, to compensate for the decrease in the concentration of the solution and therefore of the active product delivered, it is recommended to increase the volume and the frequency of renewal (Basrani and Haapasalo 2012, Moorer and Wesselink 1982).Several strategies make it possible to optimize the effect of sodium hypochlorite without increasing its concentration.Among them is the heating of the solution.It has the advantage of improving its capacity for immediate dissolution of pulp tissues without increasing cytotoxicity.In 2005, Sirtes et al.have shown that at the same concentration, heating sodium hypochlorite to 45°C increases the antibacterial action by a factor of 100 compared to a solution heated to 20°C.The ability of 1% sodium hypochlorite at 45°C to dissolve pulp tissue was found to be as effective as that of a 5.25% solution heated to 20°C.While the effect of increasing the temperature of NaOCL is proven in in-vitro studies (Sirtes et al. 2005), the transfer to the clinic is more mixed.Once the heated solution is placed inside the root canal, its temperature quickly equilibrates with that of the body.A more frequent renewal of the solution is therefore necessary.Several devices for preheating NaOCl syringes are available on the market, however a simple water bath can do the trick.The pH of the solution determines the amount of chlorine available.This balance will influence the biological effect of NaOCl (solvent power, antiseptic power).Above pH 7.6, the predominant form is hypochlorite.Below this value is hypochlorous acid.Hypochlorite solutions used in endodontics have a pH of 12, so that all available chlorine is in the form of OCl-.At identical levels of available chlorine, hypochlorous acid is more bactericidal than hypochlorite ion.One way to increase the effectiveness of hypochlorite solutions could therefore be to lower their pH (Zehnder 2006).However, hypochlorite buffered with bicarbonate makes the solution unstable without really having an influence on its antiseptic efficacy (Basrani and Haapasalo 2012, Zehnder 2006).There is no consensus on the duration of action of a solution of sodium hypochlorite at a given concentration (Zehnder 2006).For some, NaOCL is able to destroy bacteria in seconds, even at a low concentration.For others (Gomes et al 2001), a longer application time is necessary.For sodium hypochlorite to work, a minimum application time is necessary (Basrani and Haapasalo 2012).In fact, the chlorine that is responsible for the dissolving ability and antibacterial ability of NaOCL is unstable, and will be consumed rapidly during the first phase of tissue dissolution, probably in less than 2 minutes (Moorer and Wesselink 1982).Therefore, the renewal of the solution is essential (Moorer and Wesselink 1982).There is no endodontic irrigation solution that alone meets all the expected criteria (good disinfection and elimination of smear).Irrigation protocols in endodontics are based on the association of two (or even more) solutions.However, chemical interactions can exist between these solutions, some of which are harmful.The association between EDTA and sodium hypochlorite reduces the concentration of active chlorine instantaneously, thus rendering sodium hypochlorite ineffective.CHX and NaOCl interact, and an insoluble brownish-orange precipitate forms (Fig.2).The mixture of EDTA and chlorhexidine results in the immediate formation of a white precipitate (Fig.3).Fig.2: Chemical interaction between sodium hypochlorite and chlorhexidine (Basrani B. & Haapasalo M. 2012).Fig.3: Chemical interaction between EDTA and chlorhexidine (Basrani B. & Haapasalo M. 2012).In order to avoid these interactions, it is advisable to empty the channel of its contents by syringe aspiration between each change of product.Separate syringes should be used for each solution.There are two types of irrigation in endodontics:Factors that optimize passive syringe penetration are: volume (Bronnec 2010b), apical taper (Bronnec 2010b), needle gauge and type, and needle insertion level ( Bronnec 2010b).The volume of solution brought into the root canal acts both as a parameter optimizing the chemical and mechanical action of the solution.For the irrigation solution to be able to exert its action, it must be in excess in relation to the quantity of organic matter to be eliminated in order to avoid being saturated too quickly (Moorer and Wesselink 1982).It therefore seems essential to renew the solution regularly in order to maintain a high concentration of active chlorine and to compensate for its rapid consumption by the tissues.It has been shown that increasing the apical taperThere is no consensus on an optimal root canal shape (with respect to taper and diameter).The increase in the apical taper ensures better penetration and debridement of the root canal system, however a good balance between the optimization of irrigation (via root canal widening) and the weakening of the dental structure must always exist.The size of the needle influences its level of insertion, for example: a 27 G needle can reach the apex of a canal of size 40/100, the 30 G gauge up to size 30/100, and caliber 31 G up to size 25/100.The use of a needle with a large diameter leads to a reduction in the space available for the flow of the solution between the needle and the root wall.This decrease is associated with an increase in apical pressure for open-ended needles, and a decrease in solution renewal in the apical third for closed-ended needles.In endodontics, the use of a small diameter needle (30G) is recommended (Bronnec et al. 2010b).This diameter makes it possible to penetrate deeper into the canal and thus lead to better exchange and debridement in the apical third of the canal (Bronnec et al. 2010b).The shape of the needle tip influences the exchange of the irrigating solution in the last apical millimetres.Two types of needles are currently available on the market:Both shapes create a jet at their exit, but the shape of the exit conditions the orientation and the intensity of the jet (Boutsioukis 2010) (Fig.4).Fig.4: The orientation and intensity of the jet according to the different shapes of the tip of the needle.Open-ended needles (AC) and so-called safety needles (D and E).In the case of open-ended needles, the jet is very intense and extends along the root canal to the apical end.Whereas with blind needles the jet is formed on the side of the side opening.Open-ended needles showed better turnover but also increased pressure at the apical foramen.This indicates a possible risk of extrusion of the solution towards the periapical tissue (Boutsioukis 2010).Apart from the needle type, positioning the needle close to the working length could indeed improve debridement and renewal of the irrigant in the apical third of the root canal (Boutsioukis 2010, Bronnec 2010b).However, this maneuver increases the risk of solution extrusion.Therefore, a critical balance must always be maintained between effective cleaning and prevention of irrigant extrusion, especially when chemically active products are used.Optimal needle penetration can also be influenced by the size and taper of the canal and the presence of curvature.Whatever the taper, volume, and level of insertion of the needle, passive syringe irrigation will not allow complete renewal of the solution in the apical third (Bronnec 2010b).In fact, the “Vapor lock” effect (Fig.5), which designates the persistence of a gas bubble, prevents the penetration of the irrigation solution into the last apical millimeters (Tay et al 2010).To ensure good penetration, it is essential to activate the irrigating solution (Moorer and Wesselink 1982).There are several techniques for activating irrigation solutions in endodontics:Fig.5: The “Vapor lock” effect (Tay et al. 2010).It is a simple and inexpensive method which makes it possible to overcome the acquisition of a device.This technique is based on the use of a cone of gutta, called master-cone, perfectly adjusted to the final diameter of the canal as a means of activating the solution.Technique: At the end of shaping, the cone is placed in the canal, it is then animated with a back and forth movement of low amplitude (2-3 mm) for one to two minutes.This pumping movement showed a complete renewal of the irrigating solution in the apical third (Bronnec 2010b).Passive ultrasonic irrigation (IUP) consists of the activation of the irrigation solution via specific ultrasonic files.These files are inactive, so they do not allow modification of the root canal preparation, hence the term “passive”.IUP relies on the transmission of ultrasound energy through the file to the irrigating solution.Acoustic currents as well as a phenomenon of cavitation of the solution are observed (van der Sluis et al. 2007) (Fig.6).Fig.6: Effect of Irrisafe on the irrigation solution (left) and its illustration (right) (Van der Sluis et al. 2007).To this mechanical effect is added the effect of the increase in the temperature of the sodium hypochlorite, thus enabling the optimization of its antibacterial properties.Ultrasound activation has shown efficacy in removing intracanal debris.Results on smear removal remain controversial (van der Sluis et al. 2007).In France, two passive ultrasound activation files are currently available: the Endo Soft Instrument (EMS) and the Irrisafe (Satelec, Acteon).The ESI makes it possible to associate the activation and the renewal of the solution at the same time.A continuous supply of irrigation solution is ensured within the channel by the cannula of the insert.Irrisafe, on the other hand, is used by associating successive cycles of renewal and activation of the solution.Technique: At the end of shaping, the canal and the access cavity are filled with irrigating solution.The insert is then positioned stationary in the channel before being activated.Then, 3 ultrasonic activation cycles of 10 to 20 seconds per channel are performed.Between each activation cycle, a renewal of the irrigation solution is necessary.To have the desired activation effect, contacts of the ultrasonic file with the canal walls should be avoided.It is a device made up of a wireless sounding handpiece and single-use plastic inserts (Fig.7).Fig.7: Endo Activator handpiece and disposable tips in three sizes (yellow: 15/2%, red: 25/4% and blue: 30/6%).The vibration frequency of the inserts is around 10,000 cycles per minute.Three insert sizes are available: 15/2%, 25/4%, 30/6%.The choice of size depends on the apical diameter at the end of shaping.Technique: The Endo Activator is used during the final phase of irrigation.After instillation into the canal of an irrigating solution, the tip is inserted 1 mm from the working length.The Endo Activator is then turned on and the insert is moved back and forth at low amplitude for 1-2 minutes.Compared to syringe irrigation, the use of the Endo Activator allowed better penetration of the solution into the apical area without increasing the risk of solution extrusion (Desai and Himel 2009).Recently introduced by the FKG company, the XP-endo Finisher is considered a revolutionary instrument.Thanks to its zero taper and shape memory alloy, the file changes shape at different temperatures.At room temperature, the file is in its martensite phase, it is straight.However, when the file is placed in the canal, it goes into the austenite phase.During this phase, the file takes, in its last 10 mm apical, a convex shape 1.5 mm deep (Fig.8).Fig.8: The XP-endo Finisher (FKG Dentaire, La Chaux-de-Fonds, Switzerland).When rotated, the instrument will react like a whip within the irrigating solution, allowing optimal cleaning without changing the original shape of the canal.The XP-endo Finisher can be used after all root canal preparations carried out at an ISO 25 diameter or greater.Technique: Once shaping is complete, the canal is filled with the irrigation solution.Using the plastic tube, the XP-endo Finisher is adjusted to 1 mm of the working length.It is then placed at the stop of the channel, then it is set in rotation with a speed of 800 rev/min.The instrument is then moved back and forth for one minute.After one minute, the XP-endo Finisher is removed and the canal is irrigated to remove suspended debris.In recent years, the appearance of single-instrument shaping systems has allowed a significant reduction in the time spent on shaping.The aim of this reduction was to optimize the final phase of endodontic irrigation and not to reduce the overall duration of endodontic treatment.Indeed, it has been proven that irrigation in endodontics is only really effective at the end of root canal shaping (Bronnec et al 2010a).The anatomical complexities of the root canal system and the presence of biofilms are major limitations of root canal disinfection.To overcome these problems, the association between adequate shaping, a solution and a well-chosen irrigation technique are complementary.The use of an activation means seems essential.European University Diploma in Endodontology (University of Paris)Master in Applied Oral Pathophysiology, Endodontics coursePeters OA, Peters CI, Schönenberger K, Barbakow, F. 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(2012).Update on endodontic irrigating solutions.Endodontic topics, 27(1), 74-102.Van der Slui LWM, Versluis M., Wu MK & Wesselink, PR (2007).Passive ultrasonic irrigation of the root canal: a review of the literature.International endodontic journal, 40(6), 415-426.Desai P. & Himel, V. (2009).Comparative safety of various intracanal irrigation systems.Journal of endodontics, 35(4), 545-549.Register and access /dentaire365/ content