Frictional resistance of self-ligating versus conventional brackets in different bracketarchwire-angle combinations

Objective: to compare the influence of archwire material (niti,beta-ti and stainless steel) and brackets design (self-ligating and conventional) on the frictional force resistance. material and methods: two types of brackets (self-ligating brackets - smartclip,3m/unitek - and conventional brackets - gemini,3m/unitek) with three (0,5,and 10 degrees) slot angulation attached with elastomeric ligatures (tp orthodontics) were tested. all brackets were tested with archwire 0.019″×0.025″ nickel-titanium,beta-titanium,and stainless steel (unitek/3m). the mechanical testing was performed with a universal testing machine emic dl 10000 (emic co,brazil). the wires were pulled from the bracket slots at a cross-head speed of 3 mm/min until 2 mm displacement. results: self-ligating brackets produced significantly lower friction values compared with those of conventional brackets. frictional force resistance values were directly proportional to the increase in the bracket/ wire angulation. with regard to conventional brackets,stainless steel wires had the lowest friction force values,followed by nickel-titanium and beta-titanium ones. with regard to self-ligating brackets,the nickel-titanium wires had the lowest friction values,significantly lower than those of other materials. conclusion: even at different angulations,the selfligating brackets showed significantly lower friction force values than the conventional brackets. combined with nickel-titanium wires,the self-ligating brackets exhibit much lower friction,possibly due to the contact between nickel-titanium clips and wires of the same material.