Biomechanical analysis of orthodontic brackets with different closing mechanisms

The aim of the present study was to investigate the biomechanical characteristics of orthodontic bracket systems made of metal, ceramics or plastics. Six different types of brackets were studied, including the Hanson Speed (TM)- and Damon (R) 2-Brackets, both of which are equipped with specialised closing mechanisms. In addition, two conventional metal brackets (Ultratrimm (R), Discovery (R)), the ceramics bracket Fascination (R) 2 and the polycarbonate bracket Brillant (R) were investigated. Stainless steel wires with the dimensions 0.40 mm x 0.56 mm, 0.46 mm x 0.56 mm, 0.46 mm x 0.64 mm and 0.48 mm x 0.64 mm were used with each bracket type simulating the clinical rotational movement of an upper central incisor in a biomechanical set-up. A buccal crown torque of 20 was applied and the correction of the malposition was simulated experimentally. Each bracket/wire combination was analysed five times. The following parameters were analysed: maximum torquing moment, torque angle correction, and moment/torque ratio. Combining a 0.48 mm x 0.64 mm steel wire with the ceramics brackets (Fascination (R) 2) delivered the highest torquing moment (35 Nmm). The best torque correction was achieved with plastic brackets (17 degrees). The lowest moments were approximately 5.2 Nmm (Damon (R) 2, 0.40 mm x 0.56 mm steel wire), being in the range of the recommended minimum torquing moment (5 Nmm). Discovery (R) brackets delivered similar low moments. Overall, only minor differences exist between the various bracket systems with regard to their efficiency in torque correction. Clinically, the wire/slot play seems to be more important than differences in the bracket designs.