Stress evaluation of NiTi rotary files operating in a root canal with different curvature locations using finite element method

Name: Kittipong Sudjinda

Organization : Chulalongkorn University. Faculty of Engineering

Email : sudjinda.k@gmail.com

Name: Chatdanai Chiaranai

Organization : Chulalongkorn University. Faculty of Engineering

Name: Pairod Singhatanadgid

Organization : Chulalongkorn University. Faculty of Engineering

LCSH: Nickel-titanium alloys

LCSH: Endodontics

LCSH: Dental pulp cavity

LCSH: Finite element method

LCSH: Dental instruments and apparatus

Abstract: A Nikel-Titanium (NiTi) file is a widely used instrument for endodontists in root canal treatment. It was observed that a large diameter file under canal treatment has a shorter fatigue life compared to a smaller file. This observation contradicts the theoretical expectation that larger-diameter rotary files exhibit greater fatigue resistance than smaller ones. The objectives of this study are to examine the characteristics of normal stress in the NiTi rotary file when operating in curved canals, identify factors affecting stress, and evaluate whether bending of beam theory can evaluate the bending stress subjected in a rotary file. To achieve the study objectives, finite element analysis using the static structural module in ANSYS was employed to simulate NiTi rotary file model with 0.35 mm apical diameters, fully inserted into root canal models with distances from the canal orifice to the curve initiation point of 5, 6, 8, 10, and 11 mm. The rotary file model was then subjected to a 360-degree rotation. The result of the finite element method indicated that the maximum and minimum bending stresses of all fully inserted models were at the center of the bent portion of the file. During file rotation, the maximum and minimum normal stress of the file was cyclic stress. The amplitude of maximum and minimum stress obviously decreased with increasing of the distance between the canal orifice and the start of the curve, from 805.75 and -1068.3 MPa at 5 mm from the canal orifice to 577.47 and -605.18 MPa at 11 mm from the canal orifice. These results aligned with previous studies that the file with a larger diameter has a shorter fatigue life than that of a smaller diameter. When the reaction moment at the shaft of the tapered NiTi rotary file was examined, the file bent near the orifice (bent at a larger diameter) was subjected to a greater reaction moment compared to the one bent near the apical (bent at a smaller diameter). In other words, a larger diameter file is exposed to higher reaction load than a smaller diameter file. The beam theory can still be used to approximate the general tendency of the bending stress by considering the bending moment and the geometry of the beam (file) cross section

King Mongkut's University of Technology North Bangkok. Central Library

Address: BANGKOK

Email: library@kmutnb.ac.th

Created: 2024

Modified: 2025-08-15

Issued: 2025-08-15

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BibliograpyCitation : In Thai Society of Mechanical Engineers (TSME) and Kasetsart University (KU). The 14th TSME International Conference on Mechanical Engineering (TSME-ICoME14 2024) (AMM0014). Chonburi : Kasetsart University Sriracha Campus, 2024

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