ROEN0110

44 I I instrumentation _ file selection _Shortly after the excitement of the rotary file revolution wore off, the next frontier in shaping technology became the search for faster cutting efficiency. This is logically similar to our continuing search for increasingly faster computers. However, experienced clinicians started seeing overfillsfromtransportation,shortenedcanals,apical rippedcanaltermini,over-shapedcoronalregionsand cyclic fatigue failures that hadn’t occurred with their safer, slower files. The first-order question in file selection became: safe or fast? Landed-blade instru- mentswithradiused-tipgeometryweremuchsafer,in termsofavoidanceoftransportation,butnon-landed bladeswithaggressivecuttingtipswerefastercutting. TheadventofGTXFileswithM-Wirehaseliminated the difficult decision between safety and speed. They are the first rotary shaping instruments that deliver speed of cutting with safety from transportation and breakage(Fig.1). M-Wire, a new rhombohedral-phase NiTi metal used in GTX Files, has radically improved the files’ resistancetocyclicfatigue.WhileR-phase(thesweet spotbetweenaustenite-phaseandmartensite-phase NiTi) will become the new industry standard for addressing cyclic fatigue, it will never solve the problem of dangerous file geometries. The radial lands on GTX Files have been optimised by varying the width of these lands along the length of the file. This geometrical change vastly improves cutting efficiency without derangement of the canal path, a claim that no file set without lands can make (Fig. 2). Furthermore, the decreased flute angle has significantly increased GTX File’s flexibility compared with other landed instruments, simultaneously dou- bling the chip space between the flutes for a longer cutting time before clogging. Another important design feature of GTX Files is their limited maximum flute diameter. Keeping the Fig. 1_GT Series X File. Note the maximum shank diameter at 1 mm, the radiused tip, the consistent, wider blade angle and the variable- width lands. At the tip and shank ends, the land widths are half the size of the lands in the middle region of the flutes, allowing rapid cutting without transportation. Fig. 2_Micro-CT reconstruction of curved canals shaped in a mesial root of a mandibular molar, comparing outcomes in the apical third with rotary files of radiused vs. aggressive tip geometry. Note the canal on the right showing severe transportation (aggressive tip) and the canal on the right following the original canal path as the canal terminates (GTX-radiused tip). Figs. 3 & 4_Maxillary and mandi- bular molar shaped using 1–3 GTX files in each canal. Notice the fidelity to the original canal path. roots1_2010 File selection: Why geometry matters most Author_ Dr L. Stephen Buchanan, USA Fig. 1 Fig. 2

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