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Torque expression in stainless steel orthodontic brackets. A systematic review
Amy Archambault1, Ryan Lacoursiere, Hisham Badawi
1Orthodontic Graduate Program, University of Alberta, Edmonton, AB, Canada.
The Angle Orthodontist
|October 27, 2009
Summary
The engagement angle in orthodontic brackets varies with archwire and slot size, exceeding theoretical values. Clinically effective torque is achievable with specific archwire torsion in self-ligating brackets.
Area of Science:
- Orthodontic biomechanics
- Dental materials science
Background:
- Torque expression is crucial for orthodontic treatment outcomes.
- Understanding the interplay between bracket slot size and archwire dimensions is essential for predicting torque control.
Purpose of the Study:
- To quantitatively assess how varying stainless steel orthodontic bracket slot sizes and stainless steel archwire dimensions affect torque expression.
- To analyze the limitations inherent in the experimental methodologies used in existing studies.
Main Methods:
- A systematic review of in vitro studies was conducted.
- Studies measured torque expression in conventional and self-ligating stainless steel brackets using a torque-measuring device.
- Straight stainless steel orthodontic wires were used without complex mechanics or auxiliary components.
Main Results:
- Eleven articles were included, but direct comparisons were limited by methodological variations.
- Engagement angles varied significantly; for instance, in a 0.022-inch slot, angles ranged from 18 degrees (0.018 x 0.025 inch wire) to 6 degrees (0.021 x 0.025 inch wire).
- Active self-ligating brackets showed ~7.5 degrees, while passive self-ligating brackets showed ~14 degrees engagement angle with a 0.019 x 0.025 inch wire in a 0.022 inch slot.
Conclusions:
- The engagement angle is influenced by archwire dimensions, edge shape, and bracket slot size, and is generally larger than theoretical predictions.
- Clinically effective torque can be attained in 0.022-inch slots using specific archwire torsion ranges for both active (15-31 degrees) and passive (23-35 degrees) self-ligating brackets with 0.019 x 0.025 inch wires.
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