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Endo Tribune Asia Pacific Edition

The ultimate goal of endodontic treatment is the prevention and/or treatment of apical periodontitis, such that there is complete healing and absence of infection1 while the overall long-term goal is the placement of a definitive, clinically successful restoration and preser- vation of the tooth.2 Successful endodontic treatment depends on a number of factors, including proper instrumentation, successful irrigation and decontamination of the root-canal system right to the apical terminus in addition to hard to reach areas such as isthmuses, and lateral and accessory canals3,4 (Fig. 1a & b). The challenge for successful endodontic treatment has always been the removal of vital and necrotic remnants of pulp tissue, debris generated during instru- mentation, the smear layer, micro- organisms, and micro-toxins from the root-canal system.5 It has been accepted that even with the use of rotary instrumentation, the nick- el-titaniuminstrumentscurrently available only act on the central body of the root canal, resulting in a reliance on irrigation to clean beyond what may be achieved by these instruments.6 ‘Shaping canals creates sufficient space to hold an effective reservoir of irrig- ant that, upon activation, can pen- etrate, circulate and digest tissue from the uninstrumentable por- tions of the root canal system.’7,8 Several challenges often arise during root canal preparation. Some of the most common ones are anatomic factors that may pre- vent negotiation to the apical ter- mini, as well as ledge formation, perforation and file separation.The introduction of Nickel-Titanium (NiTi) alloy in endodontics pre- sented a significant improvement, allowing good results in terms of cleaning and shaping of root canals, while reducing operative time and minimising iatrogenic errors.9,10 Thanks to the superior me- chanical properties of the NiTi alloy, it was possible to use endo- dontic instruments of greater tapers in continuous rotation, in- creasing the effectiveness and rapidity of the cutting. However, several studies reported a signifi- cant risk of intracanal separation of NiTi rotary instruments.11–14 In fact, file separation via torsional and cyclic fatigue has created the biggest fear and risk for dentists using rotary NiTi files for root canal treatment.11,12,15 Although multiple factors con- tribute to file separation, cyclic fatigue has been shown as one of the leading causes.16 Fatigue failure usually occurs by the formation of microcracks at the surface of the file that starts from surface irregu- larities often caused by the grind- ing process during the manufac- turing. During each loading cycle microcracks develop, propagating getting deeper in the material, until complete separation of the file occurs.17 All endodontic files show some irregularities on the surface, and inner defect, as a con- sequence of the manufacturing process, and distribution of these defects influence fracture strength of the endodontic instruments.18,19 Since the introduction of NiTi in 198820 , varied instrument de- signs with claims of superior cyclic fatigue resistance have been prop- agated. However, there were no major changes in the manufactur- ing process/raw materials until the introduction of the second generation of NiTi files, ie, M-Wire (DENTSPLY Tulsa Dental Special- ties) in 2007 and Twisted File (TF, Kerr Endodontics Formerly Axis/ SybronEndo) in 2008. TF instruments are manufac- tured using a proprietary heat treatmenttechnologythatchanges the crystalline structure com- pletely so the triangular cross sec- tion NiTi file blank can be twisted while maintaining the natural grain structure. More precisely, TF instruments are created by taking a raw NiTi wire in the austenite crystalline structure phase and transforming it into a different phase of crystalline structure (R-phase) by a process of heating and cooling. In the R-phase, NiTi cannot be ground but it can be twisted. Once twisted, the file is heated and cooled again to main- tain its new shape and convert it back into the austenite crystalline structure, which is super elastic once stressed. The manufacturing process aims at respecting the grain structure for maximum strength as grinding creates mi- crofracture points during the manufacturing of the instruments. Because TF files are twisted and not ground, no surface microfractures occur on their surface and there- fore do not need be polished away; thereby not dulling the cutting edges and retaining their efficient cutting ability.21–23 Because of the increased flexi- bility, the TFs maintains the origi- nal 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 TF technology to improve the per- formance and safety of NiTi in- struments, the file design has also been changed with respect file dimensions, tip configuration, cross-section and flute design. More recently, a third factor has become important in this search for stronger and better instru- ments: Movement Kinematics, the branch of motion in which the objects move.26 For more than a decade, NiTi instruments have been tradition- ally used with a continuous rotary motion, but more recently a new approach to the use of NiTi instru- ments in a reciprocating move- ment had been introduced by Yared.11 The clockwise (CW) and the counterclockwise (CCW) rotations used by Yared were four-tenths and two-tenths of a circle respec- tively and the rotational speed utilised was 400rpm. The concept of using a single NiTi instrument to prepare the entire root canal was made possible due to the fact that a reciprocating motion is thought to reduce instrumentation stress. Recent literature data shows that a reciprocating motion can extend cyclic fatigue resistance of NiTi instruments when compared to continuous rotation,27,28 mainly because it reduces instrument stress. As the instrument rotates in one direction (usually the larger angle) it cuts and becomes en- gaged into the canal then it disen- gages in the opposite direction (usually with the smaller angle) and the stresses are therefore re- duced. Following these concepts new instruments have been re- cently commercialised; Reciproc (VDW) and WaveOne (DENTSPLY Maillefer), which uses specifically developed motors that produce a specific reciprocating movement (using approximately 150 to 30° angles). This reduction of instrumen- tation stress (both torsional and bending stress) is the main advan- tage of reciprocating movements. It has been shown that a lot of dif- ferent reciprocating movements can be used, each one affecting the performance and the safety of the NiTi instruments. Therefore, when discussing the advantages and disadvantages of reciprocation, the exact motion should also be mentioned, since the actual angle of reciprocation can have substan- tial influence on both the clinical and experimental behaviour of NiTi instruments.15 Another possible advantage of reciprocation could be better maintenance of original canal tra- jectory, mainly related to lower instrumentation stress and con- sequently its elastic return. How- ever, it must be underlined that reciprocation does not affect the inherent rigidity of the instru- ments. If a quite rigid NiTi instru- ment of greater taper is slightly forced into a curved canal, it will create more canal transportation than a more flexible one, due to its inherent tendency to straighten. Moreover, tip design could strong- ly influence canal transportation, ENDOTRIBUNE The World’s Endodontic Newspaper · Asia Pacific Edition Twisted files and adaptive motion technology A winning combination for safe and predictable root canal shaping By Dr Gary Glassman, Canada; Prof. Gianluca Gambarini, Italy & Dr Sergio Rosler, Argentine Published in Hong Kong www.dental-tribune.asia Vol. 14, No. 11 1a 1b Figs. 1a & b: The complexity of root canal anatomy is demonstrated by these cleared samples of maxillary molars. 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. SMALL (SM) SM1: #20/ .04 SM2: #25/ .06 SM3: #35/ .04 MEDIUM/ LARGE (ML) ML1: #25/ .08 ML2: #35/ .06 ML3: #50/ .04 Fig. 4: The motion of TFTM Adaptive instrument changes from rotary into reciprocation mode, with specifically designed CW and CCW angles which may vary from 600–0° to 370–50°.—Fig. 5: File size reference chart. 2 3 4 5 23 45

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