Comparison of load deflection properties and force level of newly introduced M5TM thermal copper NiTi with other orthodontic NiTi wires: an in vitro study

Abstract

Superelasticity and shape memory of NiTi made it popular in orthodontics for aligning and levelling of teeth. Superelasticity is a temperature induced crystallographic transformation from Austenite to Martensite (thermoelasticity). It is reflected in a load deflection graph characterised by a flat slope upon discharge known as plateau. Shape memory is the plastic deformation of NiTi from Martensite to Austenite. This can be modified by adding copper to NiTi. The clinical plateau of unloading curve represents the deactivation curve. This study is conducted to investigate the difference in the load deflection properties and the force level of M5TM thermal copper NiTi with other orthodontic NiTi wires and to plot the load deflection graph and quantify using suitable parameters. Here we tested 30 archwires, 16 were classed as traditional NiTi and 14 as heat-activated NiTi wires of three different manufacturers, G&H (Franklin, Indiana), Ormco (Orange, California), and 3M Unitek (St Paul, Minnesota). A modified 3 point bending test was performed on each archwire at a constant temperature of 37°C. For each load/ deflection curve the discharge plateau was isolated along with the mean value of average plateau force, the plateau length, and the plateau slope. Thus we compared the force expressed by each wire at specific points of deflection, and also characterised the behaviour of each archwire in the discharge phase. There is no significant difference in plateau force with respect to heat activated and traditional NiTi when using two types of wires (round and rectangular). However when comparing round wires of M5 thermal copper NiTi with other orthodontic NiTi wires of same dimension, M5 thermal copper NiTi delivered light continuous force. Among rectangular wires, 3M HANT delivered lighter force. These Shape Memory Alloys, a class of smart materials has also been widely used in the robotic manufacturing and in various other fields of robotics.