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Angle Orthod. 2012 Jul;82(4):663-9. doi: 10.2319/062011-673.1. Epub 2011 Nov 7.

Active and passive self-ligation: a myth? Part 1: torque control.

Author information

1
Orthodontic Department, University of Basel, Basel, Switzerland. lorenz.brauchli@unibas.ch

Abstract

OBJECTIVE:

To determine the amount of torque expressed by various self-ligating brackets and to evaluate the influence of active clip designs.

MATERIALS AND METHODS:

Torque moments were measured for nine different bracket types in combination with a 0.019 × 0.025 inch stainless-steel archwire. All active brackets were measured in an open and a closed configuration to evaluate the influence of the self-ligating spring clip. In addition, slot dimensions were optically measured and compared to the torque expression.

RESULTS:

Moments between 3.1 Nmm and 22.6 Nmm were observed at an angulation of 30° between archwire and slot. The amount of torque contributed by the spring clip of active self-ligating brackets was approximately 1 Nmm; 10 Nmm of torque was achieved with most brackets with a 20°-25° angulation between archwire and slot. The slot dimensions ranged from 0.0222 inch (0.563 mm) to 0.0241 inch (0.613 mm).

CONCLUSION:

The influence of the ligature or the active or passive self-ligating mechanism is minimal, and slot dimensions are far more important for the transmission of torque. The amount of torque exerted by the active spring clip is approximately 1/10th of the torquing moments recommended in the literature.

PMID:
22059468
DOI:
10.2319/062011-673.1
[Indexed for MEDLINE]

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