Three NiTi rotary systems with different cross-sectional geometries but the same sizes were selected including convex triangle (CT), S-type (S), and triple-helix (TH) with the size and taper of 25/04. Detailed 3-dimentional geometries of these three files were designed using the SolidWorks software (Dassault Systèmes, Vélizy-Villacoublay, France).
Cross-sectional and longitudinal geometries of instruments are shown inFigure 1 .
The zaxis was chosen along the length of the instruments, i.e., normal to the cross section. Root canal models with curvature angles of 45ᵒ and 60ᵒ and radii of 2 and 5mm with the same size as files (25/04) and a total length of 15mm were regenerated according to clinical information.
By combining the two cited parameters, four types of canal geometries were evaluated (Figure 2 ).
All models were transferred to ABAQUS software V2018 (SIMULIA, Providence, RI, USA) and multiple numerical simulations were performed to evaluate the stress distribution in different endodontic files. Modeled files were advanced continuously, without repetitive up and down pecking or brushing movements to reach the apex of the modeled root canals. During the insertion, the instruments rotated at the speed of 300 rpm (5 revolutions per second) and the von Mises stress distribution was evaluated based on the finite element method.
The mechanical characteristics of NiTi alloy and dentin component of the root canal were setting as: Young’s modulus 36 GPa, the Passion’s ratio 0.30, the stress range for austenite to martensite phase transformation 504-600 MPa for the NiTi alloy [ 12 (link)
] and the Young’s modulus 18.60 and the Poisson’s ratio 0.30 for dentin [ 2 (link) ].
The accumulation of plastic deformation due to cyclic loading in the pseudo-elastic range and the shear strains due to friction of the instrument blade into the canal wall were neglected as model simplifications.
Cross-sectional and longitudinal geometries of instruments are shown in
The zaxis was chosen along the length of the instruments, i.e., normal to the cross section. Root canal models with curvature angles of 45ᵒ and 60ᵒ and radii of 2 and 5mm with the same size as files (25/04) and a total length of 15mm were regenerated according to clinical information.
By combining the two cited parameters, four types of canal geometries were evaluated (
All models were transferred to ABAQUS software V2018 (SIMULIA, Providence, RI, USA) and multiple numerical simulations were performed to evaluate the stress distribution in different endodontic files. Modeled files were advanced continuously, without repetitive up and down pecking or brushing movements to reach the apex of the modeled root canals. During the insertion, the instruments rotated at the speed of 300 rpm (5 revolutions per second) and the von Mises stress distribution was evaluated based on the finite element method.
The mechanical characteristics of NiTi alloy and dentin component of the root canal were setting as: Young’s modulus 36 GPa, the Passion’s ratio 0.30, the stress range for austenite to martensite phase transformation 504-600 MPa for the NiTi alloy [ 12 (link)
] and the Young’s modulus 18.60 and the Poisson’s ratio 0.30 for dentin [ 2 (link) ].
The accumulation of plastic deformation due to cyclic loading in the pseudo-elastic range and the shear strains due to friction of the instrument blade into the canal wall were neglected as model simplifications.
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