Friction properties according to vertical and horizontal tooth displacement and bracket type during initial leveling...

To compare frictional properties according to the amounts of vertical displacement (VD) and horizontal displacement (HD) of teeth and bracket types during the initial leveling/alignment stage.

Combinations of self-ligating brackets (SLBs; two active type: In-Ovation-R and In-Ovation-C; four passive type: Damon-3Mx, Damon-Q, SmartClip-SL3, and Clarity-SL) and 0.014-inch nickel-titanium archwires (austenitic type, A-NiTi, and copper type, Cu-NiTi) were tested in a stereolithographically made typodont system that could simulate malocclusion status and periodontal ligament space. The upper canines (UCs) were displaced in the gingival direction and the upper lateral incisors (ULIs) in the lingual direction from their ideal positions by up to 3 mm, with 1-mm intervals, respectively. Two conventional brackets were used as controls. Static and kinetic frictional forces were measured. One-way analysis of variance test with post hoc test was performed for statistical analysis.

In the gingival displacement of UCs, Clarity-SL produced significantly lower frictional force (P < .001), while Damon-3Mx, In-Ovation-R, and SmartClip-SL3 produced higher frictional force among SLBs. In the lingual displacement of ULIs, Damon-Q and Damon-3Mx produced significantly lower frictional force (P < .01), while Clarity-SL produced the highest frictional force among SLBs (P < .001). Clarity-SL combined with A-NiTi and C-NiTi, Damon-3Mx combined with A-NiTi, and In-Ovation-C combined with Cu-NiTi showed differences in frictional properties between VD and HD.

Since the frictional properties of SLBs would be different between VD and HD of teeth, it is necessary to develop SLBs with low friction in both VD and HD of teeth.