Experimental study of factors affecting the failure of the cyclical nature of rotary endodontic instruments

Abstract

Relevance. The properties of shape memory, superelasticity and plasticity in nickel-titanium tools make the visual prediction of breakage as difficult as possible. Therefore, an important role is given to research, the purpose of which is to predict the time of their work and to identify the main factors affecting the probability of a fracture.Aim. Comparison of cyclic fatigue resistance of Ni-Ti rotary endodontic instruments of various manufacturers.Materials and methods. The influence of the autoclaving procedure and the angle of bending of the root canal on the resistance of a rotating endodontic instrument to cyclic loads was studied using an author's patented device that simulates the rotation of an instrument in a real channel; the number of cycles completed by each instrument before its fracture was recorded. The morphology of fractures, the microstructure of specimens under fractures, and the microhardness of specimens of endodontic instruments after testing were studied.Results. It has been established that resistance to fatigue fractures of instruments of various endodontic systems decreases with an increase in the bending angle of the root canal. For Endostar E3 Basic Rotary System tools, the number of cycles decreased by 1.2 times, for Protaper Universal tools by 2.9 times. The tools of the Protaper Next system reduced the number of cycles at a bending angle of the artificial root canal of 60 degrees by 1.5 times compared with the number of cycles at a bending angle of 45 degrees. At the same time, statistical data and the study of the microstructure of samples of new and past 6 cycles of autoclave tools did not show a connection between the autoclaving procedure and a decrease in their resistance to cyclic loads.Conclusions. When working in complex bent over 45 degrees channels, it is rational to choose an endodontic instrument that has undergone heat treatment at the production stage (in the framework of this study, it was Protaper Next 25/06 M-Wire alloy). This will reduce the likelihood of a file fracture and associated dangerous complications of endodontic treatment.

Keywords

• циклическая усталость
• автоклавирование
• никель-титановые инструменты
• механическая обработка