The purpose of this study was toinvestigate the effect of passive and active Self-ligation of aesthetic brackets on the static and kinetic friction with different wire sizes. Two types of ceramic brackets were used; Empower Clear (active self-ligating
bracket (ASLB)) and Damon Clear 2 (passive self-ligating bracket (PSLB)). They were coupled with 0.017 x 0.025-in and 0.019 x 0.025-in stainless-steel (SS) wires. A universal testing machine was used to pull the brackets along the distal end of the archwire. The test was performed at 5 mm/min crosshead speed over a distance of 8 mm to measure the static friction (SF) and the kinetic friction (KF) under dry conditions. The results showedthe PSLB's to have significantly lower SF and KF with both wire sizes.