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A nickel titanium (NiTi) rotary file is an engine-driven tapered and pointed endodontic instrument made of nickel titanium alloy with cutting edges used to mechanically shape and prepare the root canals during endodontic therapy or to remove the root canal obturating material while performing retreatment. The first NiTi file was introduced to the market in 1991. Superelasticity and shape memory are the properties that make Niti files very flexible. The high flexibility of Niti files makes them superior to stainless steel files for the purpose of rotary root canal preparation. The use of NiTi rotary files in dentistry is a common practice. ==Components== The main components of a rotary NiTi file are tip size, taper, flutes , helix angle and measuring stop. There can be other features such as redial lands and measuring lines incorporated in some designs. *Tip size — The tips size is the diameter of the tip of a file (D1) which is presented in 100th of a millimeter. Sometimes the instruments are named in a system according to what their tip sizes are numbered.The sizes range from 10-100. *Taper — The taper of a file refers to the gradual increase in diameter along its working surface. NiTi rotary files usually have a higher taper compared to the taper of standard traditional hand files which is 0.02 mm/mm (ISO taper of endodontic files, taper 0.02 mm/mm indicates 20 microns increase in diameter for every 1 mm gain in the length of a file). Their taper commonly ranges from 0.02 to 0.12 mm/mm. Different systems are sometimes classified according to their taper which can be constant or variable. *Flutes — Flutes are the grooves on the working side of the files which can be produced either by twisting or grinding a wire. Flutes provide cutting edges and also space for debris collection. Therefore, their presence turns a wire into a shaping instrument which both cuts the tooth structure and acts as an auger. The depth, width, number, arrangement and the direction of the flutes play an important role on the behavior of a file. *Helix angle — Helix angle is an angle between the cutting edge and the long access of a file. Helix angle plays an important role in debris collection and it also determines the direction of rotation. Helix angle can be constant or accelerating (changes along the length of a file). Accelerating helix angles decreases the screw in effect when most of the working surface of a file is engaged and it can decrease the torsion stress on a file. *Measuring stop — Measuring stop is a piece of rubber that an operator can use to mark certain desired length on a file while using it. Measuring stops are referred to as stoppers and they can also be color coded corresponding to the size and number of a file. *Radial land — The radial land is the peripheral portion of a rotary instrument that is flat and smooth designed to center the instrument in the central space.〔http://www.nxtbook.com/nxtbooks/aae/endodonticglossary/index.php Eleazer, P. D., Glickman, G. N., McClanahan, S. B., Webb, T. D., & Justman, B. C. (2012). Glossary of Endodontic terms.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nickel titanium rotary file」の詳細全文を読む スポンサード リンク
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