Force-deflection behavior of NiTi archwire at different configurations of bracket system

NiTi shape memory alloy archwire is widely used in orthodontic treatment, replacing stainless steel for the flat and low deactivation force it can offer. However, the presence of friction at the contact region of wire and bracket may cause the low deactivation force to be ineffective to induce tooth movement. This work evaluated the bending deformation behavior of NiTi archwire in application using conventional orthodontic stainless steel bracket in levelling treatment. Experimental test rig was developed to perform three-brackets bending test at room temperatures (27 °C). The bracket used was 0.022-in stainless steel and the archwire was 0.016-in NiTi round wire. Fabricated polytetrafluoroethylene (Teflon) bracket was used as a control experiment to represent frictionless condition of deformation on three-bracket bending. Additionally, elastomeric ligature was also used to evaluate the effect of friction produced by the elastomer. Bending tests were done at 3 different deflection magnitudes of 2 mm, 3 mm and 4 mm. The results show that bending deformation behavior of the wire on frictionless Teflon bracket produced a flat force plateau on both activation and deactivation. On the other hand, when stainless steel brackets were used, the force plateau exhibited positive gradient on the activation and negative gradient on the deactivation.