Quantified simulation of canine retraction: evaluation of frictional resistance

The purpose of this study was to evaluate the frictional resistance of various bracket/archwire combinations. The friction testing apparatus allowed dynamic and progressive bracket tipping and uprighting concurrent with linear bracket traction which experimentally approximated canine retraction with sliding mechanics. Multiple ANOVA using general linear models procedure demonstrated significant effects (P < 0.05) for bracket type, archwire type, archwire size, and archwire shape, as well as pair-wise interactions for bracket type/archwire type, bracket type/archwire size, bracket type/archwire shape, archwire type/archwire size, archwire type/archwire shape, and archwire size/archwire shape. Duncan’s multiple range test (P < 0.05) revealed the general trends regarding frictional performance of brackets and archwires tested, while Least squares means table (P < 0.05) illustrated significant interactions of pair-wise factors that differed from the general trends. It was concluded that: (1) Ceramic brackets with and without metal slots had the greatest friction followed by metal brackets, active self-ligating brackets, variable self-ligating brackets, and passive self-ligating brackets. (2) Stainless steel and braided stainless archwires measured greater friction than nickel-titanium. (3) Smaller dimension wires had less friction than larger wires, and round wires had less friction than rectangular wires. In addition, consideration of specific bracket-archwire coupling appear to reduce the frictional resistance with sliding.