Thermo-mechanical Characterization of NiTi orthodontic archwires with graded actuating forces P. Freitas Rodrigues 1,2 , F.M. Braz Fernandes 1 , R. Magalhães 1 , E. Camacho 1 , A. Lopes 1 , A. S. Paula 3 , R. Basu 4 , N. Schell 5 1 CENIMAT/I3N, Materials Science Department, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica, Portugal 2 CEMMPRE, Mechanical Engineering Department, University of Coimbra, Coimbra, Portugal 3 Mechanical Engineering and Materials Department-SE-4, Instituto Militar de Engenharia–IME, Rio de Janeiro, Brazil; 4 School of Metal Construction Skills, Bhartiya Skill Development University Jaipur, India 5 Helmholtz-Zentrum Geesthacht, Institute of Materials Research, HZG, Geesthacht, Hamburg, Germany Abstract Functionally graded NiTi orthodontic archwire was tested to assess the evolution of the actuation force as a function of the temperature. Varying actuation forces on the same orthodontic wire allow the optimization of repositioning of the different types of teeth. The wire was separated into three segments: Incisive, Premolar and Molar. The functionally graded NiTi orthodontic archwire segments have distinct structural and mechanical behavior as confirmed by differential scanning calorimetry, synchrotron- based X-ray diffraction, and thermomechanical analysis. The mechanical behavior was analyzed by three-point bending tests at four different temperatures (5, 20, 25 and 37 o C). In parallel, three-point bending tests were performed by TMA analysis in a temperature range from 5 o C (from cold water) to 40 °C (hot meal). This study showed the comparison of the different segments on the same archwire, providing a better understanding of the behavior of these functionally graded materials. Keywords: Orthodontic archwires; mechanical behavior; phase transformation temperature; functionally graded. 1. Introduction Since the beginning of the orthodontic archwire manufacturing back in the 70's, these have become more complex and convenient for different clinical cases. The orthodontic archwires are used to move the teeth with a low and continuous force. When a force is applied, the orthodontic archwire needs to display an elastic behavior during a period of weeks to months. Moreover, different stages (initial, intermediate or final) of the orthodontic treatment require different orthodontic archwires. (Melsen et al., 2007) (Proffit et al., 2013) NiTi orthodontic archwires are the most commonly used archwires at initial stage of orthodontic treatment (leveling and alignment) due to their unique properties: the shape memory effect and superelasticity. (Evans and Durning, 1996) (T. Saburi, 1998) (Melsen et al., 2007) (Riley and Bearn, 2009) (Proffit et al., 2013) These functional