DSC and three-point bending test for the study of the thermo-mechanical history of NiTi and NiTi-based orthodontic archwires

Abstract

It is a known fact that the NiTi orthodontic archwire is one of the first and most diffuse biomedical applications of shape memory alloys. In the last years, none deep study about orthodontic archwires has been conducted from the material point of view. In general, the clinical response is the principal aspect that has been investigated for this application. Nonetheless, the accurate mechanical and physical characterization of the archwires can be very important to add new developments to this biomedical product and to give a substantial contribution to the indispensable evolution that is crucial for better clinic results. In fact, the principal aspect that it is needed for further improvements is the study of the optimal force that does not cause damage to the surrounding tissues. According to this statement, a deep study about the thermomechanical characterization of several pseudoelastic commercial archwires used in the straight-wire low-friction techniques is presented. In detail, flexural mechanical tests in the three-point-bending configuration were conducted to assess the archwires unloading force, while differential scanning calorimetry was used to study the phase transition temperatures, and the thermo-mechanical history of each specimen. Both NiTi and NiTiCu commercial archwires were tested, and different geometries were considered. For all the archwires, an excellent repeatability of the results has been found. This series of characterizations provides a complete view of the thermo-mechanical properties of the material, and therefore it shows the possibility to modulate the functional properties developed by the device as a function of the biological field.

Designing Smart Biomaterials for Tissue Engineering

“…Shape-memory materials are a subset of stimuli-responsive biomaterials that change their geometry and mechanical properties with the variation of temperature or light [ 75 , 76 ], and may lead to the next generation of dynamic 3D implantable smart biomaterials [ 77 ]. Shape-memory alloys (e.g., Nitinol) have already found commercial use in orthodontic, orthopedic vascular, neurosurgical, and surgical fields, and have been well documented [ 67 , 78 , 79 ]. In the last few decades, a number of polymeric systems have been developed using a variety of functional monomers to generate block, graft, and brush copolymers, along with biodegradable constructs and crosslinked polymers; moreover, some such systems are available for biomedical applications.…”

Biomedical NiTi and β-Ti Alloys: From Composition, Microstructure and Thermo-Mechanics to Application

“…9 Ti 49 . 1 , in line with the particular composition of binary NiTi commonly used in biomedical applications [9,24].…”

“…Heating Cooling Heating Cooling For the solubilized samples, A f and Ms are of special interest (Table 4): Ti content was estimated through a graphical method where these two were compared with experimental trends observed previously [9,10], and it was determined that the two NiTi products both have Ti at 49.25-49.3 at.%.…”

“…The temperature at which the TMT occurs depends primarily on the chemical composition. It is reported that a 0.1% increase in nickel can lower the phase transformation temperature by more than 10 °C in Ni rich NiTi alloy [9,10]. The ability to adjust the transformation temperature through composition control is very useful, especially for biomedical device design.…”

CARACTERIZAÇÃO ESTRUTURAL E MECÂNICA DE FIOS ORTODÔNTICOS DE NiTi

“…Inicialmente a liga utilizada não apresentava SE ou EMF, uma vez que os efeitos eram suprimidos no processo de obtenção das ligas, devido ao alto grau de encruamento proveniente da conformação do material [4]. Parte-se do princípio que o material que promove um bom movimento dentário possui baixa força de retorno no descarregamento e continuidade desta força [4,5]. A fase martensítica era estabilizada devido à deformação plástica e sua utilização para tratamentos ortodônticos se demonstrava interessante, uma vez que o módulo de elasticidade da martensita é bem menor que o dos aços inoxidáveis usados anteriormente.…”