Abstract
Since the introduction of Nickel-Titanium alloy as the material of choice for the manufacturing of endodontic rotary instruments, the success rate of the root canal therapies has been significantly increased. This success mainly arises from the properties of the Nickel-Titanium alloy: the biocompatibility, the superelasticity and the shape memory effect. Those characteristics have led to a reduction in time of endodontic treatments, a simplification of instrumentation procedures and an increase of predictability and effectiveness of endodontic treatments. Nevertheless, the intracanal separation of Nickel-Titanium rotary instruments is still a major concern of endodontists, with a consequent possible reduction in the outcome rate. As thoroughly demonstrated, the two main causes of intracanal separation of endodontic instruments are the cyclic fatigue and the torsional loads. As results, in order to reduce the percentage of intracanal separation research and manufacturers have been focused on the parameters that directly or indirectly influence mechanical properties of endodontic rotary instruments. This review describes the current state of the art regarding the Nickel-Titanium alloy in endodontics, the mechanical behavior of endodontic rotary instruments and the relative stresses acting on them during intracanal instrumentation, highlighting the limitation of the current literature.
Highlights
The history of Endodontics is characterized by two eras, divided each other by the introduction of Nickel-Titanium (NiTi) alloy as the most eligible material for the manufacturing of endodontic rotary instruments
The factors related to the instrumentation technique and the strategy used are mainly related to the access cavity design, the choice of the setting of speed and the motion used
The improvements introduced in the endodontic technique by these instruments are extremely relevant, and here summarized in their main characteristics:
Summary
The history of Endodontics is characterized by two eras, divided each other by the introduction of Nickel-Titanium (NiTi) alloy as the most eligible material for the manufacturing of endodontic rotary instruments. In this article the Authors highlighted the limitations of the instrumentation of root canal system with stainless-steel (SS) manual files, that could be summarized in the ledge or zip formation, the canal perforation or transportation and the separation of the instruments, especially in the endodontic treatment of canals with severe curvatures [2,3,4]. These complications mainly arise from the stiffness of the SS alloy, especially with the increase of the instrument diameter.
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