Influence of the Force Delivery of Orthodontic NiTi Arch Wire on its Tribological Behavior

The complexity of orthodontic treatments requires archwires with specific biomechanical properties according to the different stages of therapy. Thanks to their wide elastic zone and low stiffness, superelastic NiTi alloy is used in the leveling and alignment phases. The friction that accompanies the beginning of treatment is a very complicated phenomenon, since in the presence of arch misalignments, the present normal force, which compresses the orthodontic archwire-bracket couple, is very dependent on the clinical situation. This study aims to identify the friction responses and the degradation mechanisms of a superelastic NiTi orthodontic archwire, as a function of the applied normal load. The latter represents the charges delivered by the archwire during its unloading, all through the first phases of treatment. Circular and rectangular samples with the most commonly used dimensions have been tested in a dry environment at room temperature. The results showed that the wear of the NiTi alloy was amplified as a function of the normal force applied for the two tested archwire shapes. Indeed, the degradation regimes observed by scanning electron microscopy present a transition, by increasing the load from a mainly adhesive regime to a more complex situation, in which wear by adhesion is accompanied by abrasive and delamination wear.

Keywords: Abrasion, Adhesion, Arch wire, Delamination, Friction, NiTi alloy, Normal Load, Orthodontic, Scanning electron microscopy, Wear.