phase in an orthodontic treatment requires them to have low stiffness, high strength and long working range. The ideal wires to use in this phase of treatment is a Nickel-Titanium archwires. Low stiffness will allow small forces to be produced when the wire is engaged in the bracket slots of teeth. High strength would prevent any permanent deformation when the wire is engaged in teeth which are severely crowded. There is evidence showing that multi-stranded superelastic NiTi wires can produce greater tooth movement than single-strand superelastic NiTi when used as the first archwire in a fixed (“train track”) brace. The use of multi-strand stainless steel vs superelastic NiTi does not have a noticeable difference in the pain experienced by the wearer. Currently more research is required to determine archwire material superiority in terms of alignment rate, time to alignment, pain and root resorption. Terms used in defining wires Stress - Internal distribution of load Strain - Internal distortion produced by the load Proportional limit - A point at which first permanent deformation is observed Yield strength - At this point, an orthodontic wire will not return to its original shape Ultimate tensile strength - The maximum load a wire can sustain Failure point - A point at which a wire breaks Modulus of elasticity - It is the ratio between stress and strain. It is measured by the slope of the elastic region. It describes the stiffness or rigidity of the material Load-Deflection Rate - It is defined as for a given load/force, the amount of deflection observed is known as the load deflection rate Stiffness - The slope of a stress/strain graph of an orthodontic wires is proportional to the stiffness of a wire. The higher the slope, the higher the stiffness. It is same as modulus of elasticity. Stiffness of the wire is proportional to a diameter of the wire but inversely proportional to the length or span of a wire. Stainless steel wire has higher stiffness than Beta-Titanium alloy which has higher stiffness than Nickel-Titanium alloy. Range - It is a range of an orthodontic wire that will bend until permanent deformation occurs. Springback - It is the ability of a wire to go through large deflections without being permanently deformed. Resilience (materials science) - It represents the energy of a wire. Formability - It is the amount of permanent bending a wire will go through before