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Tulsa dental endo files12/18/2023 ![]() Twisted files and K3XF ) have been introduced and have been reported to have improved flexibility and cyclic fatigue resistance compared to the traditional superelastic NiTi files. HyFlex CM and Typhoon Infinite Flex NiTi ), and R-phase wire (e.g. ProFile GT Series X and ProFile Vortex ), controlled memory (CM) files (e.g. ![]() Novel NiTi instruments fabricated by proprietary thermomechanical processes such as M-Wire files (e.g. Heat treatment (thermal processing) affects the fatigue resistance of NiTi instruments and is one of the fundamental ways to adjust the transition temperatures of NiTi alloys. The mechanical behaviour of NiTi alloy is determined by the relative proportions and characteristics of the microstructural phases. Even though there have been considerable improvements in the file design and manufacturing methods on endodontic rotary instruments made of NiTi alloys, intracanal fracture of rotary instruments caused by cyclic fatigue remains a concern, especially in root canals with severe curvatures. An increasing number of superelastic NiTi endodontic files with various geometrical designs has emerged during the last 20 years. The first commercially available NiTi rotary instruments came to market in the 1990s. This distinct property of NiTi alloys has created a revolution in the manufacture of endodontic instruments. Therefore, the transformation temperatures have a critical influence on the mechanical properties, and the behaviour of NiTi, which can be altered by small changes in composition, impurities, and heat treatments during the manufacturing process. Superelasticity occurs in association with a reversible phase transformation between austenite and martensite. This reversible thermoelastic martensitic transformation is the main reason for increased flexibility of NiTi instruments over traditional stainless steel instruments and facilitates instrumentation of curved root canals. This stress-induced martensitic transformation reverses spontaneously upon release of the stress the material then returns to its original shape and size. Superelasticity is associated with the occurrence of a phase transformation of the alloy upon application of stress above a critical level, which takes place when the ambient temperature is above the so-called austenite finish (A f) temperature of the material. ![]() Nickel-titanium alloy has special characteristics of superelasticity and shape memory. ![]() The crystal structure of NiTi can exist in three different states (austenite, martensite, and R-phase), which influences the physical properties of the alloy. ![]() The composition of endodontic NiTi instruments is 56% nickel and 44% titanium by weight, also expressed as a 1 : 1 atomic ratio between the elements. Nickel-titanium instruments were described 30 years ago by Walia and colleagues and brought a major breakthrough to root canal instrumentation, which has reduced most iatrogenic instrumentation complications often associated with stainless steel files. 12.1 Introduction and Classification of Current NiTi Alloy Phases The impact that these modifications have on their mechanical properties is discussed. This chapter summarises the metallurgical properties of NiTi endodontic instruments, with a special focus on the latest generation of NiTi instruments. An awareness and knowledge of the properties of nickel-titanium (NiTi) endodontic instruments and their association with the metallurgical properties is useful for clinicians to understand their behaviour in root canals and help them to make decisions regarding which instruments are appropriate for root canal treatment under certain clinical conditions. ![]()
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