Dimensional variability of orthodontic slots and archwires: an analysis of torque expression and clinical implications
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RESEARCH
Open Access
Dimensional variability of orthodontic slots and archwires: an analysis of torque expression and clinical implications Michele Tepedino1* , Giordano Paiella1, Maciej Iancu Potrubacz1, Annalisa Monaco2, Roberto Gatto2 and Claudio Chimenti1
Abstract Background: The 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. Methods: Ninety 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. Results: Slot 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. Conclusions: Due 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. Keywords: Dimensional variability, Third-order clearance, Torsional play, Real torque expression
Background The key factors for a successful outcome of an orthodontic treatment are a careful diagnosis, the patient’s compliance, an accurate treatment planning, and the coherent application of an adequate biomechanics. 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 * Correspondence: [email protected] 1 Department of Biotechnological and Applied Clinical Sciences, University of L’Aquila, Viale S. Salvatore, Edificio Delta 6, 67100 L’Aquila, Italy Full list of author information is available at the end of the article
bracket positioning, the mechanical properties of the archwire, and the precision of the slot [1]. In particular, clinicians are always struggling to achieve the full expression of the bracket’s third-order information, which is crucial to obtain a correct torque of the anterior and posterior dentition and is highly dependent on the archwire’s alloy properties [2
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