Comparison of frictional forces during the initial leveling stage in various combinations of self-ligating brackets and archwires with a custom-designed typodont system

Introduction: The purpose of this study was to compare the frictional force (FF) generated by various combinations of self-ligating bracket (SLB) types, archwire sizes, and alloy types, and the amount of displacement during the initial leveling phase of orthodontic treatment, by using a custom-designed typodont system. Methods: Two passive SLBs (Damon 2 [D2] and Damon 3 [D3]), and 3 active SLBs (SPEED [SP], In-Ovation R [IO], Time 2 [T2]), and SmartClip (SM) were tested with 0.014-in and 0.016-in austenitic nickel-titanium (A-Ni-Ti) and copper-nickel-titanium (Cu-Ni-Ti) archwires. To simulate malocclusion status, the maxillary canines (MXCs) were displaced vertically, and the mandibular lateral incisors (MNLIs) horizontally from their ideal positions up to 3 mm with 1-mm intervals. Static and kinetic FFs were measured with a speed of 0.5 mm per minutes for 5 minutes with a testing machine (model 4466, Instron, Canton, Mass). Two conventional brackets (Mini-Diamond [MD] and Clarity [CL]) were used as controls. Analysis of variance and Duncan tests were used for statistical purposes. Results: FF was increased in ascending order: D2, D3, IO, T2, SM, SP, CL, and MD in the maxillary typodont; and IO, D2, D3, T2, SP, CL, and MD in the mandibular typodont, regardless of archwire size and alloy type. The A-Ni-Ti wire showed significantly lower FF than did the Cu-Ni-Ti wire of the same size. As the amounts of vertical displacement of the MXCs and horizontal displacement of the MNLIs were increased, FF also increased. Conclusions: These findings suggest that combinations of the passive SLB and A-Ni-Ti archwire during the initial leveling stage can produce lower FF than other combinations of SLB and archwire in vitro.