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ePaper created 2016-11-22, 09:52:12 | version 1.38.0
| industry report role of the microscope 42 roots 4 2016 nals including circumferential filing using both hand and rotary files and the use of a rotary self-adjusting filethatadjuststotheshapeofthecanal.TheSAFsys- tem has been shown to be more effective in cleaning ovalcanalsthatconventionalrotarynickeltitaniumin- struments,howeverinthestudybyDeDeusetal.(2011) usingmandibularcanines,eventhistechniquedidnot render the canals completely clean. They showed that rotary files were unable to access the recesses of oval canals and that sodium hypochlorite had a “limited ability to compensate for the inadequacy of the file it- self”. They further suggested that the common belief that “the file shapes; the irritant cleans” is based more onwishfulthinkingthanonexperimentalfacts.Inare- view article by Metzger (2014), it was recognised that SAF was unable to prepare the narrow isthmus of less than 0.2 mm. In the case of the narrow isthmus the challenge is to deliver sufficient quantities of irrigant effectively into a very small area in which debris has beencompactedduringpreparation. RecentlynewconceptfilesXP3-DFinisher(Brassler, USA) that change their shape with temperature have been developed with the expectation that they can deal with canal irregularities. While these may be helpfulinremovingsofttissueinnon-circularcanals, theymaybeoflimitedvalueinsituationswheretissue or root filling materials are strongly adherent to the root canal wall. Among the numerous irrigation techniques that havealsobeenproposedtherearethosethatinclude the use of ultrasonic energy. Ultrasonic have played a role in endodontics for many years. Initially ultra- sonic canal preparation was introduced by Richman (1957)andinsubsequentyearstherewasavoguefor using the ultrasonically energised file to cut dentine in root canals. The technique fell out of favour be- cause lack of control produced ledges, apical perfo- rations and instrument separation (Lumley et al., 1992). In the 1980s research showed that passive ultrasonic energy, PUI rendered canals clean more effectively than ultrasonic irrigation with simulta- neous instrumentation (UI), where the file is inten- tionally brought into contract with the canal wall (Welleretal.,1980;Ahmadetal.,1987a).PUIusesan ultrasonically energised file to irrigate the canal and to remove debris utilising a combination of acoustic microstreamingandandcavitationalenergy(Ahmad et al., 1987a, b; 1988; 1992) (Fig. 4). PUI was found to be effective in apical part of curved canals and in the isthmus area between two canals. The technique has been shown to remove tis- sue more effectively than hand irrigation and does not cause damage to the canal wall (Gutarts et al., 2005). Variation in the efficacy of PUI reported in some studies were explained by difficulties in stan- dardisingthepositionoftheinstrumentinthecentre of the canal (van der Sluis, 2007). Since the introduction of the operating micro- scope, it has been possible to carry out endodontic treatment at varying magnifications up to approxi- mately 25x with the aid of direct light that can pene- trateintothedepthsoftherootcanal.Thismeansthat visual inspection of the prepared root canal is possi- ble. Once the canal has been shaped by conventional techniques and dried, the canal can be visually in- spectedbothapicallyandlaterallyintotheextensions of the canal. Straight canals can be inspected to the apical constriction. Since the rotary files straighten the coronal and middle thirds of curved canals, most of these prepared canals can be inspected to within a few millimetres of their full working length. Inspection through the microscope at about 10x andabovecanidentifythosepartsofthecanalsystem thathavenotbeentouchedbytherotaryfilesandcon- tainresidualtissue(Fig.5).Theseareusuallytheexten- sionsofovalandflattenedcanals,isthmusesandfins. Thechallengeistopreparetheseareasproducinga smooth predictable shape, without removing exces- sive tissue, allowing irrigants to penetrate into the canalsmorefullyandthereforeproducingcleanerca- nals. Our expectations are that delivery of irrigants and medicaments using a variety of techniques into these parts of the canal anatomy will digest residual tissue material and entomb remaining bacteria, ren- dering them ineffective. While they have undeniable advantagesinthepartsofthecanalsystemthatcan- not be inspected under the microscope, a significant part of the bacterial load within the canal can be re- movedbytheuseofacuttinginstrumentdirectedto- wards a specific part of the root canal such as a fin or isthmus. In the coronal part of the canal this can be done with either a long shank rosehead bur or a ded- icated ultrasonic instrument. Long shank burs are very limited in their use, however because of the length of the shank, relatively large diameter of the bur, lack of visual access and they can only be used in the straight part of the canal. In the deeper parts of the canal ultrasonically activated instruments can be used to great effect. Fig.4:Acoustic microstreaming patterns produced by an ultrasonically energized K-file. Fig.4 42016