A three-bracket experimental model for the evaluation of forces exerted by NiTi wires

Aim. The aim of this study was to analyze the effects of the bracket system, the wire type and the deflection level on the mechanical performances of different NiTi wires. Methods. A three-brackets experimental model was used to simulate a vertical displacement of a maxillary canine. Three different bracket systems were used: passive self-ligating brackets, active self-ligating brackets and conventional brackets with elastomeric ligatures. Each system was tested in combination with two kinds of NiTi wires of the same size 0.014-in: a superelastic wire and a thermal wire. Load-deflection tests were performed on the wires subjected to 2 and 4 mm of deflection at constant temperature of 36 °C. Results. Analysis of variance showed that the bracket system, the wire type and the wire deflection had a significant effect on the deactivation forces produced (P< 0.05). By testing Vision brackets, significantly higher deactivation forces were recorded at both 2 and 4 mm of deflection. In contrast, the lowest forces were showed by conventional brackets in all tests, due to the greater friction. Thermal wires exerted forces significantly lower than the superelastic wires in all the combinations with brackets. In the unloading phase a statistically significant decrease of the forces of NiTi wires with increasing wire deflection was observed. Conclusions. The forces of NiTi wire are significantly dependent on the various combinations of brackets and orthodontic wires