Shabnam Arbab-Chirani

Comparative analysis of torsional and bending behavior through finite-element models of 5 Ni–Ti endodontic instruments

OBJECTIVES The objectives of this study were to compare numerically the bending and torsional mechanical behavior of 5 endodontic rotary Ni-Ti instruments with equivalent size and various designs for tapers, pitch, and cutting blades.First, the geometries of Hero (20/0.06), HeroShaper (20/0.06), ProFile (20/0.06), Mtwo (20/0.06), and ProTaper F1 were generated by finite element code. Then, the 2 most representative clinical loadings, i.e., bending and torsion, were studied with an ad hoc model for the superelasticity of Ni-Ti. Bending was generated by tip deflection and torsion by a constant twist-angle of the tip. RESULTS Mechanical behavior of these 5 endodontic rotary Ni-Ti instruments could be evaluated and compared. Protaper F1 presented the greatest level of bending stress and torque. Hero and HeroShaper were more rigid than ProFile and Mtwo. CONCLUSIONS This numerical comparison evaluated the effects of the geometrical parameters on the instrumental mechanical behavior. The 5 endodontic instruments, investigated in the present study, do not have the same bending and torsional mechanical behavior. Each clinician must be aware of these behavior differences so as to use the adequate file according to the clinical situation and to the manufacturers recommendations.

An improved model of 3-dimensional finite element analysis of mechanical behavior of endodontic instruments

OBJECTIVES The aim of this study was to develop a numeric method to study the mechanical behavior of an endodontic instrument during different loading paths and to demonstrate the importance of the behavior model in the finite element results. STUDY DESIGN A numeric study of an endodontic instrument was carried out. At first, the geometry was meshed with a finite element code. Then, 3 among the most representative loadings in clinical use, i.e., bending, torsion, and nonproportional bending-torsion, were studied. Each of them was simulated by setting 3 different behaviors: elasticity, elastoplasticity, and an ad hoc model for the superelasticity. RESULTS The simulations with nonproportional bending-torsion loading showed that the mechanical behavior of Ni-Ti shape memory alloy was strongly affected by change in the loading direction. Elastic and elastoplastic models were unable to consider this feature of Ni-Ti behavior. Only a superelastic model taking into account the effects of nonproportional loading proved to respect this crucial point. CONCLUSION To realize valid simulations of the mechanical behavior of Ni-Ti instruments during different mechanical loading paths, it is necessary to use an ad hoc mechanical behavior model.