Factors affecting tooth movement in sliding mechanics.

The force system operating between bracket and wire in sliding mechanics has been examined analytically using simple beam theory with the object of providing further information on the cause of bracket binding. The results were checked on an enlarged model system, and satisfactory agreement between experiment and theory was obtained. It is shown that for a given bracket tip the restoring couple varies not only with the flexural rigidity (EI) of the wire, the bracket width and span length, but also with the position of the bracket along the span. In addition, as tipping occurs a net vertical force is brought into play which is initially intrusive, but becomes extrusive as retraction proceeds.