Effect of Tooth Angulation, Archwire Material and Vibration on Resistance to Sliding in Conventional Twin Brackets

Objective: The purpose of this study was to evaluate the effect of bracket angulation, archwire material, and vibration on the resistance to sliding of orthodontic brackets to slide along an archwire. Background: In Orthodontics, resistance to sliding generated at the wire-bracket interface has a bearing on the force transmitted to the teeth. Resistance to tooth movement in orthodontics can occur in one of two ways. One, is when a practitioner closes a space at an extraction site and the brackets slide along the archwire. The other is when teeth tip, and the angulation between the bracket and archwire produces binding and notching. In both situations, friction takes place because the archwire-bracket combination produces resistance to sliding through static and kinetic friction. For these reasons, resistance to sliding becomes a concern of all practitioners. Orthodontic appliance manufacturers frequently design innovations aimed towards improving the efficiency of tooth movement. Among these innovations are new orthodontic wires (e.g., friction-reducing Black-Ti archwire), different bracket designs (e.g., self-ligating), and the application of vibration, (e.g., AcceleDent) during active orthodontic tooth movement. Methods: In order to measure and compare resistance to sliding of orthodontic brackets along an archwire, and the effect of bracket angulation, archwire material and vibration, two test apparatuses were constructed using two simulated bone blocks. Standard 0.022” x 0.028” slot twin orthodontic brackets (0° tip, 0° torque, no offset) were bonded to maxillary first premolar typodont teeth for each of the test apparatuses. Test Apparatus 1 was assembled with a 0° angulation between the brackets’ slots bonded to each tooth. Test Apparatus 2 was assembled with a 5° angulation on the bracket located on the middle (center bracket). Three different wires: 0.019” x 0.025” Black-Ti, 0.019” x 0.025” conventional NiTi and 0.019” x 0.025” SS were ligated to the conventional twin brackets with elastomeric modules. The wires were pulled to slide along the brackets’ slots using a Universal Testing Machine at a crosshead speed of 5 mm/min for 1 minute. The vibration device was turned on the vibration group at the 0 second point, and applying 30Hz vibratory force to the teeth for the entire test. Results: Vibration significantly reduced resistance to sliding for 0.019” x 0.025” Black-Ti wire, 0.019” x 0.025” conventional NiTi and 0.019” x 0.025” SS at both 0° and 5°angulations (p0.05). The Black-Ti wire presented the highest values of all tested groups in resistance to sliding when no vibration was applied and 5° angulation between the brackets slots and the wire exist. Conclusions: The results of this in vitro study show that the degree of angulation between the wire and the brackets’ slots (5° vs 0°) was the most important variable influencing the resistance to sliding of orthodontic brackets along the archwire. Vibration plays an important role on sliding resistance, showing a statistically significant reduction in resistance to sliding in the orthodontic bracket-wire interface, when compared to the control group in which vibration was not applied