Friction does not increase anchorage loading.
Conventional wisdom suggests that orthodontists must apply added force to overcome friction during canine retraction (sliding mechanics), the result of which can be increased anchorage loading and anchorage loss. However, for a frictional force to be exerted mesially by the archwire against a canine during retraction, the archwire must be compressed between the canine and the anchor molar, and an equal but opposite force must be applied distally against the molar by the archwire. In other words, the frictional force that reduces the force of retraction on the canine must also reduce the protraction force on the molar. Emphasis on employing reduced-friction (eg, self-ligating) brackets during sliding mechanics to prevent added posterior anchorage loading is unwarranted and based more on bracket salesmanship than on orthodontic biomechanics.
Southard
Thomas E
TE
Department of Orthodontics, University of Iowa, Iowa City, Iowa 52246, USA. tom-southard@uiowa.edu
Marshall
Steve D
SD
Grosland
Nicole M
NM
D003481:Cuspid / Q000502:physiology*; D020342:Finite Element Analysis; D017276:Friction; D006801:Humans; D008963:Molar / Q000502:physiology*; D052280:Orthodontic Anchorage Procedures / Q000379:methods*; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D014087:Tooth Movement Techniques / Q000379:methods*; D016474:Weight-Bearing