Abstract
This article describes a numerical procedure for estimating the fatigue life of NiTi endodontic rotary files. An enhanced finite element model reproducing the interaction of the endodontic file rotating inside the root canal was developed, which includes important phenomena that allowed increasing the degree of realism of the simulation. A method based on the critical plane approach was proposed for extracting significant strain results from finite element analysis, which were used in combination with the Coffin–Manson relation to predict the fatigue life of the NiTi rotary files. The proposed procedure is illustrated with several numerical examples in which different combinations of endodontic rotary files and root canal geometries were investigated. By using these analyses, the effect of the radius of curvature and the angle of curvature of the root canal on the fatigue life of the rotary files was analysed. The results confirm the significant influence of the root canal geometry on the fatigue life of the NiTi rotary files and reveal the higher importance of the radius of curvature with respect to the angle of curvature of the root canal.
Highlights
IntroductionThe superelasticity of the NiTi refers to the capacity of the material for undergoing large elastic deformations that can be restored after the forces producing the deformation are released
Two different geometries of endodontic rotary file were considered, which are denoted as pitch 2 mm (P2) (Figure 1a) and pitch 3 mm (P3) (Figure 1b)
We used the Coffin–Manson relation to estimate the expected life for the file working on a representative set of root canal geometries, proposing an adequate methodology for translating finite element (FE) results to clinically relevant variables, which can be useful for manufacturers of NiTi rotary instruments
Summary
The superelasticity of the NiTi refers to the capacity of the material for undergoing large elastic deformations that can be restored after the forces producing the deformation are released. During these large deformations of the superelastic material, a phase transformation is induced within the material from austenite to martensite at a nearly constant stress. Due to this superelastic behaviour, files made of NiTi can adapt to strongly curved root canals. The main problem that persists is the fracture of the files inside the root canal [5]
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