Objectives: To measure the frictional resistance between self-ligating or conventional bracket and arch-wire at different contact angles.To analyse the effect of bracket,angulation and arch-wire material on the friction between bracket and arch-wire.Methods: Brackets to be measured in this experiment were self-ligating brackets(DamonⅢ,In-ovation) and conventional pre-adjusted metal bracket.They were upper first premolar brackets.Instron8841 universal testing machine was used to measure the frictional resistance between brackets and different kinds of arch-wires(0.016in Ni-Ti arch-wire,0.016in Australian wire,0.018×0.025in Ni-Ti arch-wire、0.018×0.025in stainless steel wire).Friction resistances were measured at different angulations(0°,3°,6°,9°).Results: The self-ligating bracket had a markedly lower friction than conventional bracket at all angulations.Following the increase of angulations,friction increased for both self-ligating bracket and conventional bracket.The increase of frictional resistance was more pronounced in the case of stainless steel and Australian wire than Ni-Ti wire.Conclusion: Bracket design,wire material and size,and contact angle significantly influence the friction between bracket and wire.Self-ligating bracket can markedly reduce the friction.
