Frictional resistance of self-ligating versus conventional brackets in different bracket-archwire-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 forceresistance.

Material and Methods

Two types of brackets (self-ligating brackets - Smartclip, 3M/Unitek - andconventional brackets - Gemini, 3M/Unitek) with three (0, 5, and 10 degrees) slotangulation attached with elastomeric ligatures (TP Orthodontics) were tested. Allbrackets were tested with archwire 0.019"x0.025" nickel-titanium, beta-titanium,and stainless steel (Unitek/3M). The mechanical testing was performed with auniversal testing machine eMIC DL 10000 (eMIC Co, Brazil). The wires were pulledfrom the bracket slots at a cross-head speed of 3 mm/min until 2 mmdisplacement.

Results

Self-ligating brackets produced significantly lower friction values compared withthose of conventional brackets. Frictional force resistance values were directlyproportional to the increase in the bracket/ wire angulation. With regard toconventional brackets, stainless steel wires had the lowest friction force values,followed by nickel-titanium and beta-titanium ones. With regard to self-ligatingbrackets, the nickel-titanium wires had the lowest friction values, significantlylower than those of other materials.

Conclusion

even at different angulations, the self-ligating brackets showed significantlylower friction force values than the conventional brackets. Combined withnickel-titanium wires, the self-ligating brackets exhibit much lower friction,possibly due to the contact between nickel-titanium clips and wires of the samematerial.