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Dental Tribune Middle East & Africa Edition | 1/2017 8 mCME New Technologies— to improve root canal disinfection mCMEarticlesinDentalTribunehavebeenapprovedby: HAADashavingeducationalcontentfor1CMECreditHours DHAawardedthisprogramfor1CPDCreditPoints CAPP designates this activity for 1 CE Credits By Drs Gianluca Plotino, Nicola M. Grande&Prof.GianlucaGambarini, Italy Introduction Themajorcausativeroleofmicro-or- ganisms in the pathogenesis of pulp and periapical diseases has clearly been demonstrated.1 The main aim of endodontic therapy is to disinfect the entire root canal system, which requirestheeliminationofmicro-or- ganisms and microbial components and the prevention of its reinfection duringandaftertreatment. Thisgoalispursuedthroughchemo- mechanical debridement, for which mechanical systems are used with irrigatingsolutions. Standardendodontic irrigationprotocol Sodiumhypochlorite Sodium hypochlorite (NaOCl) is the main endodontic irrigant used, ow- ingtoitsantibacterialpropertiesand itsabilitytodissolveorganictissue.2 NaOClisusedduringtheinstrumen- tation phase to increase its time of action within the canal as much as possible without it being chemi- cally altered by the presence of other substances.3 The effectiveness of this irrigant has been shown to depend on its concentration, temperature, pH solution and storage conditions.3 Heated solutions (45–60 °C) and higher concentrations (5–6 %) have greater tissue-dissolving properties.2 However, the greater the concentra- tion, the more severe the potential reaction if some of the irrigant is inadvertently forced into the peri- apical tissue.4 In order to reduce this risk, the use of specially designed endodontic needles and an injection technique without pressure is rec- ommended.5 EDTA The main disadvantage of NaOCl is its inability to remove the smear layer.Forthisreason,combinationof NaOCl with EDTA (ethylenediamine- tetraacetic) is recommended.2 EDTA has the ability to decompose the inorganic component of intracanal debris and is generally used in a per- centageequalto17%. EDTA appears to reduce the antibac- terial and solvent activity of NaOCl; thus, these two liquids should not be present in the canal at same time.6 For this reason, during mechanical preparation, abundant and frequent rinsing with NaOCl is performed, while the EDTA is used for 2 min at the end of the preparation phase to remove the inorganic debris and the smear layer from the canal walls completely. UltrasonicactivationofNaOCl The use of ultrasound during and at the end of the root canal prepara- tion phase is an indispensable step in improving endodontic disinfec- tion. The range of frequencies used in the ultrasonic unit is between 25 and 40 kHz.7 The effectiveness of ul- trasound in irrigation is determined by its ability to produce cavitation and acoustic streaming. Cavitation is minimized and limited to the tip of the instrument used, while the effect of acoustic streaming is more significant.7 Ultrasound creates bubbles of posi- tive and negative pressure in the molecules of the liquid with which it comes into contact. The bubbles become unstable, collapse and cause an implosion similar to a vacuum decompression. Exploding and im- ploding they release impact energy that is responsible for the detergent effect. It has been demonstrated that ultrasonic activation of NaOCl dra- matically enhances its effectiveness incleaningtherootcanalspace,asul- trasonic activation greatly increases theflowofliquidandimprovesboth the solvent and antibacterial capaci- tiesandtheremovaleffectoforganic and inorganic debris from the root canalwalls.7 Ultrasonic activation of NaOCl of 30–60sforeachcanal,withthreecy- clesof10–20s(alwaysusingnewirri- gant),appearstobesufficienttimeto obtain clean canals at the end of the preparation phase (Figs. 1 & 2).7 Ul- trasound appears to be less effective in enhancing the activity of EDTA, although it may contribute to bet- ter removal of the smear layer.7 The accumulation of debris produced by mechanicalinstrumentationininac- cessibleareasispreventablebyusing ultrasonic activation of NaOCl even during the preparation phase.8 The use of a system of ultrasonic con- tinuous irrigation might therefore beadvantageous. Itinvolvestheuseofaneedleactivat- ed by ultrasound. With this method, the irrigant is released into the canal and is activated by the action of the ultrasonicneedlesimultaneously.9 Chlorhexidine A final flush with 2 % chlorhexidine (CHX) after the use of NaOCl (to dis- solve the organic component) and EDTA (to eliminate the smear layer) has been proposed to ensure good results in cases of persistent infec- tion, owing to its broad spectrum of action and its property of substan- tivity.5, 10 However, the use of CHX is hindered by the interaction between NaOCl and CHX, which tends to cre- ate products that may discolor the tooth and precipitates that may be potentially mutagenic. For this reason, CHX should not be used in conjunction with or immediately after NaOCl.11 This interaction can be prevented or minimized by an inter- mediate wash with absolute alcohol, salineordistilledwater.12 Activationsystems Mechanical instrumentation alone can reduce the number of micro- organisms present within the root canalsystemevenwithouttheuseof irrigants and intracanal dressings,13 but it is not able to ensure an effec- tive and complete cleaning.14 Irrigat- ing solutions without the aid of me- chanical preparation are not able to reduce the intracanal bacterial infec- tionsignificantly.15 For thesereasons, todayresearchisorientedtowardthe study of systems that can improve root canal disinfection through me- chanical activation of endodontic irrigants, and in particular NaOCl. Multiple agitation techniques and systems for irrigants have been used over time,16 demonstrating more or lesspositiveresults.17 Manualagitationtechniques The simplest technique of mechani- cal activation of irrigants is manual agitation, which can be performed with different systems. The easi- est way to achieve this effect is to move vertically an endodontic file that is passive in the canal. The use of the file facilitates the penetration of the irrigant, leads to a more effec- tive delivery of irrigant to the un- touched canal surfaces and reduces the presence of air bubbles in the canal space,18 but does not improve the final cleaning.17 Another similar technique moves vertically a gutta- percha cone to working length with the canal filled with irrigant. Even this method, however, has not been found to improve the intracanal cleaning.9, 17 For this purpose, in each case, well fitting gutta-percha cones (increased taper) were more effec- tive than cones with the standard taper (0.02).9 The use of endodontic brushes and of particular needles for endodontic irrigation with bris- tles on their surface is another tech- nique suggested in order to move the irrigant more effectively within the canals. These systems have been shown to be valid in the removal of thesmearlayerfromrootcanalwalls and thus they can be recommended during irrigation with EDTA to im- prove their efficacy at the end of the preparation. Machine-assistedagitation systems Theevolutionofmanualsystemsled to the introduction of instruments that can be rotated in handpieces at low speed inside the canal filled with irrigant. They are rotary brushes too large to be brought close to the working length; thus, they can be used effec- tively only in the coronal and mid- dle thirds of the canal. Other similar instrumentsarefilesinplasticwitha smooth surface and increased taper or with a surface with lateral plastic extensions, that have dimensions appropriate to achieve the working length if used after the canal prepa- ration. Studies on these systems haveshownconflictingresults. In general, the results are better than with hand irrigation with a syringe, butlowerthanthatofothermoreef- fectivesystems.16 Continuous irrigation during in- strumentation Recently,anewsystemforrootcanal preparation has been introduced to the market. This system uses a par- ticular instrument with an abrasive surface that enlarges the canal via friction in a vibrating motion and allows irrigant to flow through the file itself. This system has shown excellent results in terms of respect- ing the anatomy and cleaning of difficult root canal anatomies, such as difficult isthmuses, oval canals or C-shaped canals.19 The low cutting efficiency of this system in some cases may limit its use in root canal preparation, but makes it an excel- lentadditionaltechniquetoenhance the cleaning and disinfection of the root canal system at the end of the preparation.20 The concept of con- tinuous irrigation was developed in the past with the use of mechanical instruments for sonic and ultrasonic preparation that could concurrently clean through the continuous re- lease of irrigant. These techniques were then abandoned for various reasonsrelatedtothepoorqualityof thepreparationitself. Sonicactivation Sonic activation has been shown to be an effective method for disin- fecting the root canals. The recent systems use smooth plastic tips of different sizes activated at a sonic frequencybyahandpiece. The system seems to be able to clean themaincanaleffectively,toremove the smear layer and to promote the filling of a greater number of lateral canals.17 Anotherrecentlyintroduced technique uses a syringe with sonic vibration that allows the delivery and activation of the irrigant in the root canal simultaneously. Sonic ac- tivation differs from ultrasonic acti- vation in that it operates at a lower frequency (1–6 kHz), and for this reason it is generally found to be less effectiveinremovingdebristhanare ultrasonicsystems.17,21,22 Apicalnegative-pressureirrigation As the irrigant must be in direct con- tact with the micro-organisms and canal walls to be effective, the acces- sibility of the irrigant to the whole rootcanalsystem,inparticularinthe apicalthird,isessential. In order to deliver the irrigant into the root canal for the entire length and to obtain a good flow of fluid, apical negative-pressure systems have been introduced that release and remove the irrigant simultane- ously. These systems consist of a macro- cannula for the coronal and middle portions and a microcannula for the apical portion, and the cannulas are connected to a syringe for irrigation andtheaspirationsystemintegrated with the dental unit (Fig. 3). During irrigation, a tip connected with a syringe delivers the irrigant to the pulp chamber without the risk of overflow, while the cannula placed in the canal pulls irrigant into the ca- nal,throughtheaspirationsystemto which it is connected, and evacuates itthroughthesuctionholes.Thissys- tem is intended to ensure a constant and continuous flow of new irrigant into the apical third safely and with a lower risk of extrusion.23 Most of the studies on this technique have shown that it is very effective at en- suring a greater volume of irrigant in the apical third24 and excellent removal of debris from this area25 and inaccessible areas,26 with results in the majority of cases similar to those of ultrasonic activation tech- niques.27–29 From a clinical perspec- tive, apical negative-pressure sys- tems can be effectively integrated withultrasonicirrigationtechniques becausetheyactbydifferentmecha- nisms. They can operate in synergy with the objective to obtain cleaner canals, especially in the apical third andthemostinaccessibleareas. Laseractivation The interaction between the laser and the irrigant in the root canal is a new area of interest in the field of endodontic disinfection. This con- cept is the base of laser-activated ir- rigation (LAI) and photon-initiated photoacousticstreaming(PIPS)tech- nology.30 The mechanism of this interaction has been attributed to the effec- tive absorption of the laser light by NaOCl.Thisleadstothevaporization of the irrigant and to the formation of vapor bubbles, which expand and implode with secondary cavitation effects. The PIPS technique is based on the power of the Er:YAG laser to create photoacoustic shock waves within the irrigant introduced into the ca- nal. When it is activated in a limited vol- ume of liquid, the high absorption Figs.1&2:Ultrasonicactivationwithapassivefile(Fig.1)andanactivefile(Fig.2). ÿPage9