Superelastic nickel-titanium archwires, unlike conventional wires, are capable of withstanding very large deflections and on returning to their original shape on deactivation will produce more moderate forces. The region over which there is a 'plateau' depends on the deflection and is greater the larger the deflection. With most wires both the initial wire stiffness in bending and the 'plateau' deactivation loads are very dependent on temperature. Wire size is no longer a guide to wire behaviour and force values for a given temperature and for wires of the same nominal diameter from different manufacturers can vary by a factor of six.