An evaluation of the torsional moments developed in orthodontic applications. An in vitro study.

The amount of play between brackets and wire and the magnitude of the torsional moments developed have been investigated for six different rectangular wires. The study simulated the situation occurring when torque is applied to an individual central incisor. The observed play between wire and bracket ranged from about 5 degrees between an 0.018 x 0.025 inch in an 0.018-inch bracket slot, to approximately 20 degrees for a 0.016 x 0.022 inch in an 0.018-inch bracket slot. The observed rate of change after the play had been eliminated, varied from 0.24 degrees/Nmm to 0.37 degrees/Nmm for the steel wires, whereas 0.017 x 0.025-inch nitinol had a rate of change of approximately 1.07 degrees/Nmm. The use of ligatures demonstrated that a torque effect could be observed even though the play had not been completely eliminated.