Abstract
Heat treatments and geometries have a significant influence on the mechanical behavior of endodontic files. Finite element analyses were performed to verify the effects due to each of these parameters in NiTi files. Two designs and three NiTi atomic structures (resultant from different heat treatments) were selected for this study. The geometries of the ProTaper Next X1 and ProTaper Universal S2 files, and the structures of fully austenitic (conventional superelastic), austenite treated, and fully R-phased were used. The mechanical responses were evaluated under flexion and torsion loading conditions described by ISO 3630-1 specification. According to the results, the design of the X1 file exhibit higher flexibility in comparison to the S2 model. Under torsional loads, S2 showed higher stiffness. The structures of fully austenitic showed the least flexibility under flexion and the highest torsional stiffness. The stress levels reached for the austenitic condition were uppermost. The treated condition that resulted in a fully R-phase file usually presented a higher level of flexibility with lower stress levels, indicating a longer life in fatigue when compared to the other treatments.
Highlights
The use of NiTi alloys in endodontic instruments had an enormous impact on endodontic practice
Three-dimensional models were created using computer‐assisted design (CAD) software SolidWorks 2016 to reproduce the current geometries of the ProTaper X1 and ProTaper Universal S2 files (Figures 1a and b, respectively)
The heat treatment at 450 °C resulted in higher flexibility than the heat treatment at 350 °C
Summary
The use of NiTi alloys in endodontic instruments had an enormous impact on endodontic practice. These alloys exhibit greater flexibility when compared with stainless steel[1]. Despite the advantages of NiTi over stainless steels, NiTi endodontic files may exhibit unexpected fractures within the root canal[4]. The torsional fracture occurs when the file gets locked into the canal, whilst the shaft continues to rotate. The flexural failure occurs due to the material’s fatigue: the instrument rotates within a curved channel and experiences alternating traction/compression loads, resulting in fatigue[4,6,7,8]
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