Superelastic materials displaying different force levels within one archwire.

Recently archwire materials have become available which are claimed to be capable of exerting different force levels within one arch. Such orthodontic archwires are of importance because the forces they exert are supposed to be better adapted to different physiological force levels as required by teeth with different root surface areas. Undesired side effects such as root resorptions and pain should thus be minimized. The purpose of this study was to test these types of wires and to evaluate whether and, if so, to what degree the claimed properties are present. Load-deflection curves of 6 superelastic nickel-titanium orthodontic wires by 4 manufacturers were recorded using a simple beam bending test at mouth temperature. Activation-deactivation cycles with varying maximum deflection were achieved using a computer controlled stepper motor. Each archwire was tested at 4 different points on the wire. The resulting forces were evaluated metrically and graphically. Great differences were found between the superelastic properties claimed by the manufacturers and the observations of this study and also between the different products. Only 2 of the tested wires showed superelastic properties on a force level that seems adapted to the needs of the teeth to be moved.