The influence of bracket design on moment production during axial rotation.

The interaction between the bracket of an axially rotated tooth and arch wire produces a moment. This moment influences tooth movement and rotational control and is itself influenced by bracket width and bracket ligation. Self-ligating spring clip brackets fasten to and interact with arch wires differently than conventionally ligated brackets. An in vitro study with a simulated orthodontic model was undertaken to evaluate the effects of bracket width and ligation technique on the moment production of conventional and self-ligated brackets during axial rotation. Bracket widths ranged from 1.890 mm (0.0744 inch) to 2.809 mm (0.1106 inch). Steel tie, elastomeric, and self-ligating spring clip ligation techniques were used. Empirically, both bracket width and ligation technique significantly effect the moment produced during axial rotation. For the range of bracket widths and types evaluated, ligation technique was found to have a greater influence on moment production than did bracket width. The self-ligated spring clip bracket delivered the least force over the greatest range of axial rotation.

A comparative study of frictional forces between orthodontic brackets and arch wires.

An in vitro study of simulated canine retraction was undertaken to evaluate the difference in frictional resistance between stainless steel arch wires and steel and ceramic brackets with elastomeric, steel, and self-ligation. Each bracket slot was 0.018 x 0.025 inch. The arch wires used were 0.014-inch, 0.016-inch, 0.018-inch, 0.016 x 0.016-inch, and 0.016 x 0.22-inch stainless steel. A testing apparatus was designed to attempt to simulate the clinical situation in which teeth tip slightly while they slide along the arch wire. Under these testing conditions, the self-ligating steel bracket did not demonstrate less friction than the elastic or steel-ligated stainless steel brackets. For most wire sizes, elastomer-ligated ceramic brackets demonstrated the greatest friction when compared with other bracket/ligation technique combinations. The clinical significance of this study becomes apparent when stainless steel brackets are used on the posterior teeth and ceramic brackets are used on the anterior teeth. If sliding mechanics are used, the anterior teeth may be more resistant to movement than the posterior teeth because of the greater friction of the ceramic brackets. This could result in more posterior anchorage loss than would be expected if only one type of bracket were used.

Asymmetric space closure.

In a vertically slotted 0.022 X 0.028 inch edgewise system, the use of a two-dimensional ribbon arch--0.022 X 0.016 inch from lateral incisor to lateral incisor and 0.016 X 0.022 inch from the canine to the molars--plus an uprighting spring on the canine maintained incisor position while unilaterally protracting a molar-premolar unit by means of sliding mechanics. Five degrees of labial crown torque was placed in the incisor portion of the wire and the uprighting spring exerted a force of 200 to 250 g. The intra-arch force applied to protract the molar--premolar unit was 300 to 350 g.