Abstract: Abstract: Objectives To study the friction forces of stainless steel(SS) archwires with different sizes and rocking chair curvature (RCC) in Empower self-ligating brackets (Empower SLB) so as to guide the orthodontists′ choice of the brackets and archwires.Methods The standard occlusal plaster model was selected as the study model,and it was bonded with the Empower SLB and buccal tubes in a dry condition.Then the frictional forces of two rectangular SS archwire sizes(0.46 mm×0.64 mm and 0.48 mm× 0.64 mm) with four RCC(0°,5°,10°,and 15°) which made 8 combinations were tested.Results According to the RCC of 0°,5°,10°,and 15° loaded by 2 rectangular stainless steel(SS) archwire sizes from the canines to the secondary premolar segment,(1) In all combinations,dynamic friction was slightly less than the maximum static friction; (2) With the same RCC,0.46 mm×0.64 mm SS had less frictional force than 0.48 mm×0.64 mm SS (P<0.05).(3) Archwires of the same size increased as RCC (0°,5°,10°,15°)increased,and the frictional force also gradually increased (0.46 mm×0.64 mm SS:0＜0.19 N＜0.35 N＜0.90 N; 0.48 mm×0.64 mm SS:0＜0.26 N＜0.43 N＜1.00 N.P<0.05).Conclusions The dynamic friction is slightly less than the maximum static friction in Empower SLB.The frictional force gradually increased with the growing of SS sizes and RCC.

Key words: Frictional Force, Rocking Chair Curvature, Empower Self-ligating Bracket, Stainless Steel Archwire