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Title: In vitro biomechanical analysis of torque capabilities of various 0.018″ lingual bracket-wire systems: total torque play and slot size.
Author: Daratsianos N, Bourauel C, Fimmers R, Jäger A, Schwestka-Polly R.
Journal: Eur J Orthod; 2016 Oct; 38(5):459-69. PubMed ID: 26518759.
Abstract:
OBJECTIVES: To determine the total torque play of various rectangular titanium molybdenum alloy (TMA)/stainless steel (SS) wires in various 0.018″ upper incisor lingual brackets and slot size measurements. METHODS: TMA (0.0175″ × 0.0175″, 0.0170″ × 0.025″, 0.0182″ × 0.0182″, 0.0182″ × 0.025″) and SS wires (0.016″ × 0.022″, 0.016″ × 0.024″, 0.018″ × 0.025″) were twisted in standard (Hiro, Incognito™, Joy®, Kurz 7th generation, STb™: fixation with elastic modules) and self-ligating brackets (Evolution SLT®, In-Ovation® L MTM: closed ligation mechanism) from -20 degrees to +20 degrees with a custom-made machine. The total torque play was calculated by extrapolating the linear portion of the twist/moment curves to the x-axis and adding the absolute negative and positive angle values at the intercepts. The bracket slot height was measured before and after the experiments with a series of pin gauges with round profile. RESULTS: Brackets in ascending order for total torque play with the most slot-filling wire TMA 0.0182″ × 0.025″: Evolution SLT® (0 degree ± 0 degree), Incognito™ (2.2 degrees ±1.1 degrees), Hiro (5.1 degrees ±3.0 degrees), In-Ovation® L MTM (6.3 degrees ±2.2 degrees), STb™ (6.6 degrees ±1.8 degrees), Kurz 7th generation (7.1 degrees ±0.8 degrees), and Joy® (12.0 degrees ±0.8 degrees). Wires in ascending order for total torque play with the most precise slot Incognito™: TMA 0.0182″ × 0.025″ (2.2 degrees ±1.1 degrees), TMA 0.0182″ × 0.0182″ (2.4 degrees ±0.9 degrees), SS 0.018″ × 0.025″ (5.5 degrees ±1.0 degrees), TMA 0.0170″ × 0.025″ (9.4 degrees ±1.8 degrees), TMA 0.0175″ × 0.0175″ (13.0 degrees ±1.5 degrees), SS 0.016″ × 0.024″ (16.1 degrees ±1.4 degrees), SS 0.016″ × 0.022″ (17.8 degrees ±1.0 degrees); differences between some of the experimental groups were not statistically significant. Bracket slot dimensions in ascending order: Evolution SLT® (less than 0.452mm), Incognito™ (0.460mm ±0.002mm), In-Ovation® L MTM (0.469mm ±0.001mm), Hiro (0.469mm ±0.010mm), STb™ (0.471mm ±0.002mm), Kurz 7th generation (0.473mm ±0.002mm), and Joy® (greater than 0.498mm). LIMITATIONS: The applied method must be questioned when used with brackets with incomplete slot walls (Evolution SLT®). Slot measurement with pin gauges may not register bracket wing deformation. CONCLUSIONS: All brackets showed a differing slot size from the nominal 0.018″ (0.457mm). Incognito™ presented the most precise and Joy® the widest slot. The main wires for the retraction phase SS 0.016″ × 0.022″/SS 0.016″ × 0.024″ showed poor torque control. Among the finishing TMA wires, TMA 0.0175″ × 0.0175″ exhibited the highest and TMA 0.0182″ × 0.0182″/TMA 0.0182″ × 0.025″ the smallest torque play. SIGNIFICANCE: The manufacturers could profit from this investigation towards optimization of the dimensional precision of their products. The orthodontist must be aware of the torque play of the wire-bracket combinations to be able to plan and individualize the appliance by third order customization.

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