Assessment of surface friction of self-ligating brackets under conditions of angulated traction

objective: the aim of this study was to assess resistance to sliding of stainless steel passive self-ligating brackets with 0° and 2.5° angulations and to compare them to active self-ligating brackets at zero angulation. the hypothesis to be tested was that passive self-ligating brackets produce lower frictional forces than active self-ligating brackets. methods: twenty five 0.022 x 0.028-in slot maxillary canine brackets were divided into 5 groups of 5 brackets: damon sl ii (ormco, ca, usa) self-ligating bracket and gemini (3m/unitek, ca, usa) conventional bracket with angulation of 0 and 2.5° and a group of speed 2 (american orthodontics, wi, usa) active clip self-ligating system with zero angulation. twenty five segments of stainless steel 0.020-in archwire (tp orthodontics, in, usa) were tested and each bracket/wire interface was evaluated at 4 successive points during sliding. overall, 100 frictional values were analyzed by parametric analysis of variance and bonferroni tests. results and conclusion: frictional tests were performed with an emic dl 10000 testing machine (emic, brazil) with a load cell of one kilogram. passive self-ligating brackets produced lower frictional forces than active self-ligating brackets (p < 0.01). under angulation, brackets with a slide mechanism produced higher friction than the same brackets under zero angulation (p < 0.01). nevertheless, the slide system under angulation produced smaller friction values than conventional brackets tied with elastomeric ligatures in 0° tests.