A Comparative Study Of Frictional Force Between Free-edge Bracket And Conventional Bracket

Objectives: Through testing frictional force of combinations of brackets and archwires with different ligature force, testing frictional force of Free-edge brackets and conventional brackets coupled with different archwires, testing frictional force of combinations of brackets and archwires with different roughness, influencing factor of frictional force of combinations of brackets and archwires was analyzed, which could provide reference to select brackets,archwires and the type of ligation reasonably.Methods: In the dry states, the static and kinetic frictional force of combinations of 4 kinds of brackets and 4 kinds of archwires with 4 different kinds of ligature forces was tested, the static and kinetic frictional force of combinations of 2 kinds of Free-edge brackets and 2 kinds of conventional brackets coupled with 4 kinds of archwires were tested, the static and kinetic frictional force of combinations of Chinese made brackets and archwires coupled with imported brackets and archwires was tested.Results: 1. The frictional force of combinations of brackets and archwires had statistical significant difference among different ligature force(p<0.01), the frictional force of combinations of brackets and archwires increased with ligature force, the couples ligated with elastomeric O-rings had greater frictional force than those tied with the equivalent normal force of 300g, the couples ligated with 0.25mm stainless steel ligature wires had greatest frictional force, when the brackets were ligated with elastomeric O-rings ,the equivalent normal force was approximately 300g-500g, when the brackets were ligated with 0.25mm stainless steel ligature wires, the equivalent normal force was approximately 1500g-1800g. 2. The frictional force of Free-edge bracket ligated with middle wings was small to zero, there were statistical significant difference compared with both Free-edge bracket ligated with six wings and conventional bracket ligated with four wings(p<0.01); Free-edge bracket ligated with six wings had greater frictional force than conventional bracket ligated with four wings, there were statistical significant difference between them(p<0.01). 3. The combinations of Chinese made archwires coupled with Chinese made brackets had greater frictional force than those of Chinese made archwires coupled with imported brackets, there were statistical significant difference between them(p<0.01);but the combinations of imported archwires coupled with Chinese made brackets had lower frictional force than those of imported archwires coupled with imported brackets, there were statistical significant difference between them(p<0.01).Conclusions: 1. The frictional force of combinations of brackets and archwires increased with ligature force, when the brackets were ligated with elastomeric O-rings ,the equivalent normal force was approximately 300g-500g, when the brackets were ligated with 0.25mm stainless steel ligature wires, the equivalent normal force was approximately 1500g-1800g. 2. Free-edge bracket had unique ligature structure with six wings, which not only could be ligated with middle wings generating low frictional force, but also be ligated with six wings generating great frictional force, it solved the contradiction between less frictional force and better tooth control, it improved the capability of the series of edgewise fixed appliance, the application of it would increase the effectiveness of orthodontic treatment. 3. The combinations of Chinese made archwires coupled with Chinese made brackets had greater frictional force than those of Chinese made archwires coupled with imported brackets, the combinations of imported archwires coupled with Chinese made brackets had lower frictional force than those of imported archwires coupled with imported brackets.