Frictional resistance in orthodontic brackets with repeated use.

This study measured and compared the level of frictional resistance generated with a nonrepeated and repeated experimental design to evaluate whether the wear in the bracket slot will influence frictional resistance. Both 0.018 and 0.022 inch slot size edgewise brackets were tested in a specially designed apparatus. The frictional resistance was measured on an Instron Universal Testing Machine. A repeated measures ANOVA was used to determine differences among the 10 individual bracket wire specimens for each combination to study the influence of wear on static and kinetic frictional force. A paired t test (two-tail) procedure was used to compare the static and kinetic frictional forces in the nonrepeated and repeated study for each bracket slot, wire size, and bracket type. The results show that there was a distinct trend for the mean frictional force to be higher with the repeated use of the brackets.