Abstract
BackgroundThe loss of third-order information in pre-adjusted brackets due to torsional play is a problem in clinical orthodontics. The aim of this study was to evaluate the impact of slot height, archwire height, width and edge bevel’s radius on the torsional play for three brackets/archwire systems.MethodsNinety brackets with a 0.022 × 0.028 in. slot with McLaughlin-Bennett-Trevisi prescription from three different manufacturers were selected, and the slot’s height and depth were measured using a profile projector. Sixty stainless-steel rectangular archwires from three different manufacturers were sectioned and observed with a SEM to measure their height, width, and radius of edge bevel. The recorded data were used to calculate the theoretical torsional play between different slot−archwire combinations. One-way ANOVA was used to compare the measurements within different bracket types and among different manufacturers.ResultsSlot height was usually oversized. Archwire’s height was usually undersized, but oversized wires were also observed. The radius edge bevel was the most variable parameter. A certain degree of torsional play is always present that differs from one bracket type to another of the same producer and that can even be doubled from one manufacturer to another.ConclusionsDue to production tolerance, differences between the nominal values and the real dimensions of any components of a slot/archwire system are common. This results in a torsional play that limits torque expression. The archwire’s edge bevel plays an important role in torque expression, and clearer information should be provided by the manufacturers regarding this aspect.
Highlights
The loss of third-order information in pre-adjusted brackets due to torsional play is a problem in clinical orthodontics
The slot depth showed a greater variability, with Group 1 showing the greatest increment, and Group 3 showing the greatest differences with the Bracket for the upper right first premolar (UR4) brackets having a smaller depth (− 12.1% and − 21.7% for the maximum and minimum depth, respectively)
When looking at archwire measurements (Fig. 5), both height and width of all the tested archwires were generally undersized from − 0.4 to − 1.4%, except for the archwires from Group 3, which were slightly oversized from +0.4 to +0.8% (Table 4)
Summary
The loss of third-order information in pre-adjusted brackets due to torsional play is a problem in clinical orthodontics. When using straight-wire appliances, a satisfying outcome depends, among other things, on a precise expression of the bracket’s prescription, which is a result of the. This intimate fit is seldom achieved because there is always a variable lack of contact between the bracket’s slot and the archwire that limits tooth movement control. Large torsional play values result in an ineffective or in a slow orthodontic treatment [6], because the clinically achieved torque will be equal to the bracket’s torque minus the amount of torsional play The presence of this torsional play depends on both the ligation method and the accurate respect of the nominal dimensional values of slots and archwires [7]. There are some technical standards, like the ISO standards (International Organization for Standardization) that regulate the dimensional parameters and the tolerance limits that every industrial product must respect: in the orthodontic field, there are the ISO 15841 (https:// www.iso.org/standard/62223.html) for archwires and the ISO 27020 (https://www.iso.org/standard/72549. html) for brackets and tubes
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