4. Binding Friction of NiTi Archwires at Different Size and Shape in 3-Bracket Bending Configuration

During orthodontic treatment, the force released by the bent of a NiTi archwire is influenced by the friction developed in the bracket system. This in vitro study investigated the amount of friction encountered by the NiTi archwire in a 3-brackets configuration. Five different sizes within two shapes of NiTi archwire were considered for the bending test at different deflection magnitudes of 2, 3 and 4 mm. The binding friction was measured by comparing the force-deflection curve of the NiTi archwire with the use of polytetrafluoroethylene (Teflon) bracket and stainless steel brackets. The force result from the Teflon bracket was considered as a control test, utilizing its frictionless character. This investigation revealed that the binding friction is affected by the archwire size and shape. The NiTi archwire experienced higher binding friction during activation and slightly lower during the wire recovery at deactivation. The magnitude of the binding friction gradually increased with the increase of the archwire size and shape, with the largest binding friction of 7.6 N recorded from the 0.457 mm × 0.635 mm rectangular archwire and the smallest binding friction was recorded from the 0.356 mm round archwire.