Study on bending behaviour of nickel–titanium rotary endodontic instruments by analytical and numerical analyses

Abstract

AimTo develop analytical models and analyse the stress distribution and flexibility of nickel–titanium (NiTi) instruments subject to bending forces.MethodologyThe analytical method was used to analyse the behaviours of NiTi instruments under bending forces. Two NiTi instruments (RaCe and Mani NRT) with different cross-sections and geometries were considered. Analytical results were derived using Euler–Bernoulli nonlinear differential equations that took into account the screw pitch variation of these NiTi instruments. In addition, the nonlinear deformation analysis based on the analytical model and the finite element nonlinear analysis was carried out. Numerical results are obtained by carrying out a finite element method.ResultsAccording to analytical results, the maximum curvature of the instrument occurs near the instrument tip. Results of the finite element analysis revealed that the position of maximum von Mises stress was near the instrument tip. Therefore, the proposed analytical model can be used to predict the position of maximum curvature in the instrument where fracture may occur. Finally, results of analytical and numerical models were compatible.ConclusionThe proposed analytical model was validated by numerical results in analysing bending deformation of NiTi instruments. The analytical model is useful in the design and analysis of instruments. The proposed theoretical model is effective in studying the flexibility of NiTi instruments. Compared with the finite element method, the analytical model can deal conveniently and effectively with the subject of bending behaviour of rotary NiTi endodontic instruments.

In vitro evaluation of efficacy of different rotary instrument systems for gutta percha removal during root canal retreatment

“…In addition, its minimum tip size being #30, does not penetrate into apical gutta percha where the apical part is prepared to sizes lesser than #30. Original NRT rotary instruments had a limitation of decreased flexibility, resulting in inability to go around canal curvatures ( 23 ). This may also hold true in case of NRT retreatment files which compromises GP removal efficacy.…”

A comparison of two reciprocating instruments using bending stress and cyclic fatigue tests

“…Similarly, the ranges of simulated canals with different angles and radii of curvature are large, as is the range of materials examined, which vary from acrylic resin blocks to metal tubes and conformations of canal models using electroerosion. 23,24,25 In this study, a battery of tests was performed to measure flexibility to 45°. In the traction machine, the vertical displacement of the instrument was 15.55 mm, a value obtained using trigonometry (sin 45°).…”

Evaluation of Pressure Distribution against Root Canal Walls of NiTi Rotary Instruments by Finite Element Analysis

“…FEA was firstly introduced in endodontics for the static analysis of the forces applied to the NiTi files [15][16][17][18]21]. Afterwards, a dynamic FEA was proposed for the visualization of the instrument mechanical stresses during shaping [17][18][19][29][30][31][32]. In all these studies, the differences found between the instruments were due to the geometry of the instruments and to the alloy stiffness: especially, it was demonstrated how the most rigid instruments caused the highest stress on the apical portion of the canal, confirming that these two instrument characteristics influence their mechanical behavior [4,19,26,33,34].…”