Bracket angulation as a function of its length in the canine distal movement.

The slot angulations that are built into currently manufactured brackets are the same as those recommended more than 20 years ago. Because of a continuous trend toward miniaturization, the bracket slot length has diminished considerably, fact that should have had an impact on the characteristics of the slot. This impact has not yet taken place. A decrease in the overall bracket size and the shortening of the slot length invite unaccounted tooth rotation, which happens when an attempt is made to adhere to traditional angulations. If only a pure translation of a tooth is wanted, such a rotation becomes undesirable. To reduce its action, power arms are used. Unfortunately, these do not solve the problem. Indeed, to overcome this effect, a modification of the values of standard angulations is needed. To illustrate the point, maxillary canine retraction is considered, because it is both common and involves an already high bracket slot angulation. With standard solid mechanics and statics, new angulations are proposed as functions of the bracket slot length and arch wire rigidity. In addition, an estimation of the minimum useful size of the slot is made.