Abstract
Objectives The aim of this study was to investigate the changes of the crystal lattice of NiTi instruments after repeated autoclave sterilization cycles based on the results to conclude about the influence of multiple sterilization on the characteristics of ProTaper clinical use. Methods 21 samples of ProTaper Universal rotary files were divided into 3 groups of 7 samples. After 1, 4, and 7 cycles of sterilization, the samples were observed using еnergy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). Results EDS analysis confirmed that all samples were composed mainly of nickel and titanium, also Fe (presumably steel), Cr, Co, and Zn were found. The percentage of nickel and titanium was affected by repeated sterilization cycles. The mass fraction of Fe, Co, Zn, and Cr decreased after 1, 4, and 7 sterilization cycles. According to the results of the second study, it was found that, with increasing autoclaving cycles, the percentage of Fe decreased. There were changes in the three obtained diffractograms, which indicated an increase in the number of the martensitic phase and a decrease in austenitic. The cutting efficiency of the ProTaper is also reduced during repeated sterilization cycles, which can be caused by the austenitic and martensitic phase displacement. Conclusion Manufacturing features and repeated sterilization cycles increase the internal deformation in the structure of NiTi alloy, which increases the risk of fracture.
Highlights
Nickel-titanium (Ni-Ti) rotary endodontic files are widely used in dentistry due to their distinctive properties: high flexibility, shape memory effect, and superelasticity [1,2,3,4]
It was confirmed that ProTaper Universal rotary files consist of nickel (56.2 ± 1.2%) and titanium (41.2 ± 0.9%) and the material containing Fe
Ch, Co, and Zn were revealed in the samples. e mass fraction of Fe, Ch, Co, and Zn decreases with an increase in the number of reautoclaving, followed by the disappearance of the first three listed elements (Table 1)
Summary
Nickel-titanium (Ni-Ti) rotary endodontic files are widely used in dentistry due to their distinctive properties: high flexibility, shape memory effect, and superelasticity [1,2,3,4]. NiTi rotary endodontic instruments have enhanced the effectiveness of endodontic treatment with regard to accuracy, reduction of apical foramen transportation, and procedural time since their introduction into clinical practice nearly 3 decades ago [5, 6]. E ProTaper Universal (PTU) system (Dentsply Maillefer, Ballaigues, Switzerland) is a NiTi rotary system of instruments manufactured with progressive tapering over the length of the cutting blades, convex triangular cross sections, and noncutting tips. In the PTU system, the file is produced in such a way that it does not cut the ends, and its cross section is a convex triangle. Autoclaving helps in minimizing the risk of crossinfection during endodontic treatment [10]. Autoclaving helps in minimizing the risk of crossinfection during endodontic treatment [10]. ere are different reports on autoclaving effects that improve [11] or degrade [12] both the performance and physical properties of different rotary Ni-Ti systems
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