10/4/2023 0 Comments Endodontic rotary file systemsTherefore, despite success in fragment removal in many cases, prevention of file fracture is important.Įndodontic hand files can be used to clean and shape root canals. Removal of additional dentin by special burs and ultrasonic tips during the removal of the fragment may weaken the root. Removal of fractured file from root canal can be challenging and time-consuming, with documented success rates ranging from 55% to 80%. ![]() A fractured fragment of an instrument affects the treatment prognosis, especially when infection is present, because it makes further cleaning and disinfection of the canal difficult. Torsional failure takes place when the instrument (usually tip) engages and binds within the canal, but the remainder of the file continues to rotate, generating stresses beyond the ultimate strength of the material. Flexural fatigue is induced by recurrent compressive and tensile strains at the site of maximal flexure when the instrument rotates and moves freely up and down in a curved canal. The failure mechanisms of NiTi instruments have been thoroughly investigated. However, unpredictable fracture that may occur during instrumentation of root canals still remains a concern. NiTi instruments offer better elastic flexibility in bending and twisting, as well as superior mechanical properties, when compared to conventional stainless steel files. Since nickel-titanium (NiTi) material was introduced to endodontic industry for manufacturing files in 1988, NiTi alloys have undergone metallurgical improvements. ![]() The factors related to torque generation are also discussed. This review focuses on the stress generated to the teeth and the instrument during instrumentation under various experimental conditions. This stress has been measured using various experimental approaches, including microcrack observation by using a microscope or computed tomography, attaching strain gauges to the teeth, and finite element analysis. Therefore, understanding of torque and stress generated is important to prevent the fractures to the instrument and the teeth. The generated stress may induce the strain accumulation on NiTi instrument and the canal wall and lead to the development of microcrack in the instrument and dentinal wall. The process of root canal shaping by rotary instruments is a series of actions that requires torque and generates stress to both the teeth and the NiTi instruments. The endodontic engine maintains a constant rotational speed by adjusting torque regardless of the root canal conditions. ![]() Torque is defined as the force required to rotate the NiTi file and can be considered of as a parameter for the stress generated. Unintended sudden fracture can occur during root canal shaping, and it is important to understand the conditions that may cause instrument fractures. As the use of nickel-titanium (NiTi) file systems for root canal therapy has become popular hence, knowledge and understanding of the characteristics of NiTi files is essential for dentists.
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