Stress distribution of three NiTi rotary files under bending and torsional conditions using 3-dimensional finite element analysis

Article information

Restor Dent Endod. 2008;33(4):323-331

Publication date (electronic) : 2008 July 31

doi : https://doi.org/10.5395/JKACD.2008.33.4.323

Tae-Oh Kim ¹, Chan-Joo Lee ², Byung-Min Kim ², Jeong-Kil Park ¹, Bock Hur ¹, Hyeon-Cheol Kim ¹

¹Department of Conservative Dentistry, School of Dentistry, Pusan National University, Busan, Korea.

²Division of Precision Manufacturing Systems, Pusan National University, Busan, Korea.

Corresponding Author: Hyeon-Cheol Kim. Department of Conservative Dentistry, School of Dentistry, Pusan National University, 1-10, Ami-Dong, Seo-Gu, Busan, 602-739, Korea. Tel: 82-51-240-7978, golddent@pusan.ac.kr

Received 2008 April 07; Revised 2008 May 13; Accepted 2008 May 15.

Abstract

Flexibility and fracture properties determine the performance of NiTi rotary instruments. The purpose of this study was to evaluate how geometrical differences between three NiTi instruments affect the deformation and stress distributions under bending and torsional conditions using finite element analysis.

Three NiTi files (ProFile .06 / #30, F3 of ProTaper and ProTaper Universal) were scanned using a Micro-CT. The obtained structural geometries were meshed with linear, eight-noded hexahedral elements. The mechanical behavior (deformation and von Mises equivalent stress) of the three endodontic instruments were analyzed under four bending and rotational conditions using ABAQUS finite element analysis software. The nonlinear mechanical behavior of the NiTi was taken into account.

The U-shaped cross sectional geometry of ProFile showed the highest flexibility of the three file models. The ProTaper, which has a convex triangular cross-section, was the most stiff file model. For the same deflection, the ProTaper required more force to reach the same deflection as the other models, and needed more torque than other models for the same amount of rotation. The highest von Mises stress value was found at the groove area in the cross-section of the ProTaper Universal.

Under torsion, all files showed highest stresses at their groove area. The ProFile showed highest von Mises stress value under the same torsional moment while the ProTaper Universal showed the highest value under same rotational angle.

Keywords: Stress; NiTi rotary instrument; Cross-section; Bending; Torsion; Finite element analysis

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This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Figure 1

Cross-sectional and longitudinal geometry of three NiTi files. A; ProFile .06 / #30, B; ProTaper F3, C; ProTaper Universal F3.

Figure 2

Final FE models of three NiTi files used in this study: A; ProFile .06 / #30, B; ProTaper F3, C; ProTaper Universal F3.

Figure 3

The stress-strain curve of the NiTi material22).

Figure 4

Simulated conditions used in this study: A; The simulated condition of free-end loading of 1 N, B; The simulated condition of same bending distance, C; The torsional condition of 2.5 Nmm with 4 mm fixation, D; The same rotational condition of 10° with 4 mm fixation.

Figure 5

The deflection and stress distribution under the free-end loading. A; ProFile .06 / #30, B; ProTaper F3, C; ProTaper Universal F3.

Figure 6

Horizontal row A shows the von Mises stress distribution under the condition of 2 mm deflection. Row B shows the von Mises stress distribution under the condition of 2.5 Nmm torsional moments. Row C shows the von Mises stress distribution under the condition of same rotational angle.

Figure 7

Graph A showing the bending moment needed to deflect. Graph B showing the torque required to rotate the file under the restrained condition.

Table 1

Calculated deformation and maximum von Mises equivalent stress results for three NiTi rotary instruments under four loading conditions. Location of the bending deformation was at the tip of the file, the maximum stress concentration locations were measured from file tip