it breaks. Ductility - It is an ability of the wire to sustain a large amount of permanent deformation without being ruptured. Biocompatibility - A biocompatible wire would be resistance to corrosion and would be tolerant to the tissues of oral mucosa Shape-memory alloy - It is an ability of the wire to remember its original shape after being plastically deformed Twinning - It is a property of a metal that refers to a movement that divides lattice into two symmetric parts. Deformation in certain structures occurs by twinning. The niti alloys are characterized by multiple, rather than single, twinning through metal. Hysteresis - Hysteris in orthodontics is associated with the Nickel-Titanium wires. It is the difference between temperature of the starting phase of a Niti wire and a finishing phase of a Niti wire. It can also be known as difference in temperature when a Niti wire goes from its Austenitic (high temperature) state to a Martensitic (low temperature) state. Quenching - Rapid cooling of a material after it is annealed. It leads to material losing its strength but gaining its ductility Annealing (metallurgy) - Process of heating a material which leads to material gaining strength and losing its ductility References Orthodontic appliances