Computational study on the effect of contact friction towards deactivation force of superelastic NiTi arch wire in a bracket system

This study investigated the impact of contact friction towards force-deflection behavior exhibited by superelastic NiTi arch wire during orthodontic treatment. A three-dimensional finite-element model of wire bending in bracket configurations was developed by employing UMAT/Nitinol and contact interaction. This model was used to predict the force response of NiTi wires upon bending at different friction conditions; friction coefficient at the wire-bracket interfaces was varied from 0.0 to 0.5. The force from the finite-element model was validated against experimental work, and good agreement was obtained between the two results. This investigation revealed that the superelastic wires exhibited the forces over a plateau trend in a frictionless bracket system. As the friction coefficient at the wire-bracket interface increased, the force plateau gradually transformed into a slope trend, suppressing the deactivation force to a lower magnitude. Over the increment of the friction coefficients, the rectangular wire registered the largest force reduction and slope variation at a ratio of −12.7 N/μ and −4.6 Nμ mm⁻¹, respectively. Also, under the condition of high contact friction coefficient (μ ≥ 0.4), the deactivation force is suppressed to zero and inhibits tooth movement. (paper)