Frictional forces related to self-ligating brackets

Abstract

SUMMARY Orthodontic tooth movement can be regarded as teeth sliding on a wire like pearls on a string, the force being supplied by springs or elastics. The movement implies friction between wire and bracket, taking up part of the force and leaving an uncontrolled amount to act on the teeth. The friction is likely to depend on bracket construction and wire material. Therefore, in this investigation the friction of self-ligating brackets and beta-titanium wires was evaluated, as opposed to more conventional configurations.Carried by low-friction linear ball bearings, a bracket was made to slide along an outstretched archwire with minimal (and known) basic friction, either parallel or at an angle to the wire. Two self-ligating brackets were used in their closed position without any normal force. Friction was tested against four wires: stainless steel and beta-titanium, both in round and rectangular cross-sections. The force used to overcome friction and to move the bracket was measured on a testing machine at 10 mm/min, and the basic friction was subtracted.The results show that round wires had a lower friction than rectangular wires, the betatitanium wires had a markedly higher friction than stainless steel wires, and friction increased with angulation for all bracket/wire combinations. The self-ligating brackets had a markedly lower friction than conventional brackets at all angulations, and self-ligating brackets, closed by the capping of a conventional design, exhibited a significantly lower friction than self-ligating brackets closed by a spring.The selection of bracket design, wire material, and wire cross-section significantly influences the forces acting in a continuous arch system.

Evaluation of friction produced by self-ligating, conventional and Barbosa Versatile brackets

“…It allows for passive trapping of the wire (except in the interactive brackets with larger diameter wires) without the involvement of any outside connecting agent and allows the use of lighter forces due to reduced friction, which helps to preserve the anchorage 3,9,10,14,17,18,21 .…”

“…It is essential to consider that during canine retraction, the lower the rate of friction, the lower will be the requirement of the anchorage elements. When the frictional resistance was compared between self-ligating brackets using beta-titanium and stainless steel wires in round and rectangular configurations, the round wire produced less friction than the strength of rectangular wires, and the betatitanium wires showed markedly more friction than the steel wires 14 . It has also been demonstrated that increasing the angle produced a greater amount of friction, and self-ligating brackets showed less friction than conventional types.…”

“…There is increasing resistance to sliding as the angles increase [7][8][9][10][11][12][13] . Considering the types of brackets, the self-ligating system has lower frictional forces compared with conventional types 9,10,[12][13][14][15][16][17][18] . The Barbosa Versatile (BV) bracket 19 design may provide lower frictional force, greater sliding, and require less anchorage.…”

Self-Ligating Brackets: An Overview

“…With a 0.021 x 0.025" wire, the SPEED bracket produced significantly greater friction than either the Mobil-Lock or Activa brackets. In a similar study, Pizzoni et al,1998, compared the Damon SL bracket to the SPEED bracket with an active clip and two conventionally ligated brackets. The two self-ligating brackets were not statistically different for a 0.018" wire, but when 0.017 x 0.025" wires were used, the active clip on the SPEED bracket produced significantly greater friction than the passive Damon bracket.…”

Self‐ligating brackets in orthodontics: do they deliver what they claim?

“…[4][5][6] Damon described the clinical use of his Damon brackets and proposed that this low friction is a major factor in enabling more efficient treatment. 7 However, the assumption has been made that along with low friction in vitro, comes more rapid alignment and a reduction in treatment time in the clinical setting.…”