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ePaper created 2016-09-05, 09:33:59 | version 1.38.0
atomic factors that may prevent negotiation to the apicaltermini,aswellasledgeformation,perforation and file separation. The introduction of Nickel-Titanium (NiTi) alloy in endodontics presented a significant improvement, allowing good results in terms of cleaning and shap- ing of root canals, while reducing operative time and minimising iatrogenic errors.9, 10 Thankstothesuperiormechanicalpropertiesofthe NiTi alloy, it was possible to use endodontic instru- ments of greater tapers in continuous rotation, in- creasingtheeffectivenessandrapidityofthecutting. However, several studies reported a significant risk of intracanal separation of NiTi rotary instruments.11–14 In fact, file separation via torsional and cyclic fatigue hascreatedthebiggestfearandriskfordentistsusing rotary NiTi files for root canal treatment.11, 12, 15 Although multiple factors contribute to file sepa- ration, cyclic fatigue has been shown as one of the leadingcauses.16 Fatiguefailureusuallyoccursbythe formation of microcracks at the surface of the file thatstartsfromsurfaceirregularitiesoftencausedby the grinding process during the manufacturing. During each loading cycle microcracks develop, propagating getting deeper in the material, until completeseparationofthefileoccurs.17 Allendodon- tic files show some irregularities on the surface, and innerdefect,asaconsequenceofthemanufacturing process, and distribution of these defects influence fracture strength of the endodontic instruments.18, 19 Since the introduction of NiTi in 198820 , varied instrument designs with claims of superior cyclic fatigue resistance have been propagated. However, there were no major changes in the manufacturing process/raw materials until the introduction of the second generation of NiTi files, ie, M-Wire(DENTSPLYTulsaDentalSpecial- ties) in 2007 and Twisted File (TF, Kerr EndodonticsFormerlyAxis/SybronEndo)in 2008. TF instruments are manufactured using a propri- etary heat treatment technology that changes the crystalline structure completely so the triangular crosssectionNiTifileblankcanbetwistedwhilemain- taining the natural grain structure. More precisely, TF instruments are created by taking a raw NiTi wire intheaustenitecrystallinestructurephaseandtrans- forming it into a different phase of crystalline struc- ture(R-phase)byaprocessofheatingandcooling.In the R-phase, NiTi cannot be ground but it can be twisted. Once twisted, the file is heated and cooled againtomaintainitsnewshapeand convert it back into the austenite crystallinestructure,whichissuper elasticoncestressed.Themanufac- turing process aims at respecting the grain structure for maximum strength as grinding creates mi- crofracture points during the man- ufacturing of the instruments. Be- cause TF files are twisted and not ground,nosurfacemicrofracturesoccurontheirsur- face and therefore do not need be polished away; thereby not dulling the cutting edges and retaining their efficient cutting ability.21–23 Because of the increased flexibility, the TFs main- tains the original canal shape better, minimises canal transportation and stays centred even in severely curved root canals.24, 25 In addition to the development of heat treated TFtechnologytoimprovetheperformanceandsafety of NiTi instruments, the file design has also been changed with respect file dimensions, tip configura- tion, cross-section and flute design. More recently, a third factor has become important in this search forstrongerandbetterinstruments:Move- ment Kinematics, the branch of motion in which the objects move.26 For more than a decade, NiTi instruments havebeentraditionallyusedwithacontinuous Fig.2: Colour-Coded File Identification. An intuitive,colour-coded system designed for efficiency and ease of use.Just like a traffic light – start with green and stop with red. Fig.3: ElementsTM Motor.Settings for TFTM Adaptive,TFTM ,K3,Lightspeed, M4 Safety Handpiece and custom settings for personal preference. canal shaping technique | 15 roots 3 2016 Fig.3 Fig.2 32016