Although the nickel-titanium（Ni-Ti） alloy with super-elastic property is more and more used in endodontics, it has been reported that rotary Ni-Ti instruments are more prone to intracanal fracture compared with stainless steel instruments. These unexpected fractures occur without any visible changes to the instruments which produce a prominence problem creating a major obstacle to normally routine therapy. Many studies showed that the presence of defects on and in the Ni-Ti instruments before used restrict clinical application. In recent years, considerable attempt has been undertaken to improve these condition and produced more flexible and resistant Ni-Ti endodontic instruments, which may minimize the occurrence of fractures. This article reviewed the development of manufacturing methods of Ni-Ti endodontic instrument.
