These are the radius of curvature, angle of curvature of the canal, the length of the arc, the diameter, and the design of the instrument. There are several factors that can affect cyclic fatigue resistance of a file. On the inside of the curvature of a canal, a rotating file is compressed, and the outside of the curvature, the file undergoes tension. This type of fracture can be seen as a result of fatigue, most often caused from the excessive stresses of the repetitive compression and tension that occurs during rotation of a file around a curvature. Another fracture may take place across the grain of the metal with little or no apparent deformation. ![]() This is accompanied by an apparent deformation of a file, and the separation occurs as a result of slippage between the planes of its crystalline boundaries, mainly due to the excessive forces of torsion. Torsional fatigue occurs when the tip of the instrument binds in the root canal, while the file continues to rotate. identified two modes of fracture for a rotary NiTi file: torsional fatigue and cyclic fatigue. ![]() ![]() The significant advantage of NiTi alloy is its unique ability to negotiate curvatures during continuous rotation without undergoing the permanent plastic deformation hence, preparations are self-centered in the canal which helps to maintain the original root canal configuration.įerreira et al. The success of endodontic treatment relies on shaping of the root canal system by eradicating bacteria which facilitates adequate chemical irrigants to disinfect the root canal system and create space for root canal filling.1980's saw the new era of endodontic instruments developed from nickel–titanium (NiTi) alloy that has improved the mechanical preparation of root canal space, avoiding problems associated with stainless steel instrument such as ledges, zipping, stripping, perforation, and root canal transportation.
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