Article Evaluation of Fatigue Life for Dental Implants Using FEM Analysis Babak Ziaie * and S. Mohammad Reza Khalili   Citation: Ziaie, B.; Khalili, S.M.R. Evaluation of Fatigue Life for Dental Implants Using FEM Analysis. Prosthesis 2021, 3, 300–313. https://doi.org/10.3390/ prosthesis3040028 Academic Editor: Bruno Chrcanovic Received: 29 August 2021 Accepted: 20 September 2021 Published: 23 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Centre of Research for Composite and Smart Materials and Structures, Faculty of Mechanical Engineering, K. N. Toosi University of Technology, Tehran 1991943344, Iran; smrkhalili2017@gmail.com * Correspondence: babak.ziai@gmail.com Abstract: The purpose of this study is to numerically analyze a 3D model of an implant under fatigue loads. A bone and a V shape implant were modeled using SolidWorks2008 software. In order to obtain an exact model, the bone was assumed as a linear orthotropic material. Mechanical loads were applied in terms of fastening torque to the abutment and mastication force applied at the top of the crown. The abutment was tightened into the implant by applying a 35 N.cm torque causing tensile stress within the abutment screw as a preload that is harmful not only for the fatigue life of the abutment, but also for the stability of the implant-abutment interface. A 700 N force at an angle of 30 degrees to the vertical direction was applied to the crown. The mechanical analysis results showed that the abutment is the critical component of the implant system in terms of fatigue failure. This is due to the fact that the tensile preloads originated from the fastening torque. The results were presented in terms of fatigue life in the abutment. Fatigue life of the abutment and implant were calculated based on the Goodman, Soderberg, Smith–Watson–Topper (SWT), and Marrow theories. According to the results of the fatigue life prediction, abutment screws may fail after about 3 × 10 5 cycles. The predicted results by the Goodman theory are at a very good accordance with the clinical data. Keywords: dental implant; mechanical stress; fatigue life; FEM; abutment failure 1. Introduction For many years, dental implants have been studied as a replacement for missing teeth. The performance of implants is extremely related to their stability, resistance against applied loads, and minimization of the stress they impose to the jaw bone. Implants are produced in different shapes and sizes, so as to decrease the distribution of the stress in BII (bone implant interface) and implant components. As the implant is continuously under mechanical loads and stresses, it is essential to perform fatigue analysis to evaluate the fatigue life. Titanium implants were first applied by Branemark in 1965 [1]. Since then, many modifications have been made to the initial design in order to improve the performance of the implants. However, due to limitations confining experimental studies, numeri- cal analyses were used widely. FEM (finite element method) analysis helps to have a better understanding of the effects of different variables in the implant structure on its performance. Akpinar et al. presented a 2D model to study the stress distribution and stress concentration within the implants [2]. In 2002, Holmgren et al. used a 2D model to survey the effect of osseointegration level on implant stress [3]. When a horizontal load is applied to a simulated mandible, the location and direction of maximum stress around the dental implants appeared to be influenced much more by the structural charac- ters of the mandibles when compared with vertical loads [4]. The results of some of 2D models are often far from the actual situation and the stresses predicted by a 2D model are less accurate than that of 3D counterpart [5]. Thus, in-vitro models have been widely Prosthesis 2021, 3, 300–313. https://doi.org/10.3390/prosthesis3040028 https://www.mdpi.com/journal/prosthesis