Objectives: Self-ligating brackets are widely believed to be more effective in clinical use and to involve less friction and force. Thus, the goal of this in vitro investigation was to experimentally assess the effectiveness of different bracket-archwire combinations and the force levels exerted in two-dimensional direction during correction of tooth malalignment. An important aspect of this objective was to determine whether the behaviors of conventional bracket systems with an elastic or steel ligature differ from that of self-ligating brackets.
Materials and methods: Three conventional (Mini Taurus®, RMO; Synergy®, RMO; Victory Series™, 3M Unitek) and three self-ligating bracket systems (Speed™, Strite; Smart Clip™, 3M Unitek; Time 3, American Orthodontics) were analyzed. All brackets had 0.018-inch (0.46-mm) slots and--except for the self-ligating brackets-were tested with both a steel ligature (0.25 mm; Remanium, Dentaurum) and an elastic rubber ligature (1.3 mm in diameter; Dentalastics, Dentaurum). They were fitted with four different round wires: a 0.30-mm stainless steel (3M Unitek), 0.38-mm stainless steel coaxial (Advanced Orthodontics), 0.30-mm Thermalloy NiTi (RMO), and 0.30-mm Orthonol NiTi (RMO) archwire. The orthodontic measurement and simulation system (OMSS) was used to simulate a two-dimensional (2 mm of infraocclusion and 2 mm of vestibular displacement) malalignment of tooth 21 inserted in a resin replica of a Frasaco model. Four brackets of the same type were assessed and four individual measurements taken per bracket to analyze initial force systems and corrective malalignment outcomes.
Results: The initial force systems and tooth movements varied distinctly between the different material combinations in conjunction with the ligation systems and archwire types used. The force systems generated were readily reproducible across individual measurements. Leveling outcomes and force systems between conventional steel-ligated and self-ligating brackets coincided in most cases. Both of these device configurations corrected the malalignment by 78-99 % on average. Rubber-ligated conventional brackets, by contrast, performed significantly worse due to exertion of significantly higher forces and 60 % less of a leveling effect.
Conclusion: Our investigation demonstrates that both conventional steel-ligated brackets and self-ligating brackets, which are highlighted in the literature as highly efficient systems, lead to equivalent corrective outcomes in the treatment of tooth malalignments.