Abstract
Finite element analysis was used to evaluate the stress distribution, estimate the residual stresses, bending, and amount of displacement of two nickel-titanium instruments manufactured by the same M-wire technology but with different cross-section.Materials and methodsTwo brands of Ni-Ti instruments ProTaper NEXT (Dentsply Maillefer), and WaveOne (Dentsply Maillefer, Ballaigues, Switzerland) were scanned with stereomicroscope to produce a two-dimensional model for each file using computer-aided design programs (CAD) (SolidWorks software package), which then was converted into stereolithographic extension to be readable by programming software (MATLAB software) to produce three-dimensional models. The mathematical analysis of files was performed on SolidWorks software package. The mechanical behavior of the two files was analyzed numerically in a SolidWorks package to simulate and measure torsion, bending, and file displacement. Application of a shear moment (torsion) 2.5 N/mm moment of force was applied to the shaft in a clockwise direction, while the last 4 mm of the tip was rigidly constrained to evaluate the stress distribution on each file. As for Cantilever bending, a concentrated load of 1 N at the tip of the file with its shaft rigidly held in place was applied for the finite element models. The vertical displacement was measured and the von Mises stress distribution was evaluated.ResultsThe WaveOne file showed higher torsional stresses accumulation than those accumulated in the ProTaper NEXT. While the ProTaper NEXT showed more bending and file displacement than those showed by WaveOne file.ConclusionsThe two files rotary models highlighted the different mechanical properties of the files although they share the same manufactured technology M-wire. The ProTaper NEXT showed less torsional stress accumulation and more bending properties.
Highlights
Nickel-titanium (NiTi) rotary instruments are preferred than other endodontic instruments during the mechanical preparation of the root canal system due to their high flexibility (Walia et al, 1988), their tendency of being able to stay more centered in the canal (Esposito & Cunningham, 1995), and preparing the canal within its original axis, causing less canal transportation (Glossen et al, 1995)
Finite element analysis Bending test During bending test the von Mises stress on ProTaper finite element (FE) model recorded 923 Mega Pascale (MPa) bending stresses, which was higher than that recorded in WaveOne FE model that recorded 583.1 MPa as shown in Table 1, and the distributions of Von Mises bending stresses were illustrated in Figs. 5 and 6
Torsion test During torsion test WaveOne FE model recorded 753.7 MPa Von Mises stresses, which was more than that in ProTaper FE model 608 MPa as shown in Table 3, and the distributions of von Mises torsion stresses was illustrated in Figs. 7 and 8
Summary
Nickel-titanium (NiTi) rotary instruments are preferred than other endodontic instruments during the mechanical preparation of the root canal system due to their high flexibility (Walia et al, 1988), their tendency of being able to stay more centered in the canal (Esposito & Cunningham, 1995), and preparing the canal within its original axis , causing less canal transportation (Glossen et al, 1995). In spite of these advantages, rotary NiTi files have major complications, concerning their fracture or separation within the canal during root canal shaping. Many manufacturing strategies and methodologies have been developed for NiTi rotary instruments to improve their flexibility and resistance to fracture. (Elnaghy, 2014; Lopes et al, 2013; Park et al, 2010)
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