Active and passive self-ligation: a myth? Part 1: torque control.

Abstract Objective: To determine the amount of torque expressed by various self-ligating brackets and to evaluate the influence of active clip designs. Materials and Methods: Torque moments were measured for nine different bracket types in combination with a 0.019 × 0.025 inch stainless-steel archwire. All active brackets were measured in an open and a closed configuration to evaluate the influence of the self-ligating spring clip. In addition, slot dimensions were optically measured and compared to the torque expression. Results: Moments between 3.1 Nmm and 22.6 Nmm were observed at an angulation of 30° between archwire and slot. The amount of torque contributed by the spring clip of active self-ligating brackets was approximately 1 Nmm; 10 Nmm of torque was achieved with most brackets with a 20°–25° angulation between archwire and slot. The slot dimensions ranged from 0.0222 inch (0.563 mm) to 0.0241 inch (0.613 mm). Conclusion: The influence of the ligature or the active or passive self-ligating mechan...