Influence of the Ligation Method, Metallic Alloy and Tipping in Sliding Mechanics

Introduction: Since the development of orthodontic fixed appliances, bracket design has undergone many modifications in order to improve treatment efficiency. In the last decades, the popularity of self-ligating brackets has grown based on manufacturers claims of lower friction, faster ligation, less chair time, fewer appointments, shorter treatment time, increased comfort and less pain. The resistance to bracket sliding is a main factor influencing treatment time and eventually the outcome of the orthodontic treatment, therefore is important to ascertain how different bracket prescriptions respond to friction. The aim of this study was to evaluate, in vitro, the resistance in sliding mechanics of conventional ligated brackets and of both active and passive self-ligating brackets when using stainless steel and nickel-titanium archwires; and the effect of tipping on the resistance to such sliding mechanics. Material and Methods: The 0.022-inch slot brackets Damon® Q™; Prodigy SL™; Smart-Clip™SL3; Victory Series™; Morelli® Roth Standard and Morelli® Roth SLI were tested. The brackets were ligated to 0.016x0.022 inch stainless steel and nickel-titanium archwires. A tipping of 0° or 5° was added to the wires. For each combination of bracket/archwire, 10 sliding tests were performed with the Shimadzu AG-1 5kN testing instrument. Results: A higher resistance to the sliding was observed with the conventional ligated brackets when compared with the self-ligating brackets, passive or active. There were no statistical differences either between the resistance of active and passive self-ligating brackets or between the resistance of both types of orthodontic archwires for an angulation of 0°. The stainless steel archwires demonstrated a higher resistance for an angulation of 5°. There were no statistical differences between 0° and 5° of tipping. Conclusion: The self-ligating brackets are an useful tool in orthodontic mechanics, when low levels of friction are needed. When used with small diameter archwires, the resistance to sliding is not affected by small angulations and small degrees tipping. Nevertheless, different metallic alloys present dissimilar behaviour when angulations are present. Keywords: Sliding Mechanics, Self-ligating brackets, Friction, Resistance