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Torque stability of plastic brackets following multiple loading and artificial material aging--an in-vitro comparison
Matthias Möller1, Arndt Klocke, Reza Sadat-Khonsari
1Department of Orthodontics, Eberhard Karl University, Tübingen, Germany. info@kfo-moeller.de
Summary
Plastic orthodontic brackets, especially those without metal slots, demonstrate poor torque stability under repeated loads. Only plastic brackets with a metal slot are clinically viable compared to steel brackets.
Area of Science:
- Orthodontics
- Materials Science
- Biomaterials Engineering
Background:
- Plastic brackets are increasingly used in orthodontics.
- Their load-deflection behavior and torque stability under repeated forces are critical for clinical efficacy.
- Understanding material fatigue and elasticity is essential for bracket design.
Purpose of the Study:
- To compare the load-deflection behavior of various plastic orthodontic brackets under repeated torque loads.
- To evaluate the torque stability and material fatigue of different plastic bracket materials against steel brackets.
- To analyze the influence of bracket slot design and material reinforcement on torsional forces.
Main Methods:
- Artificial aging of polycarbonate and polyurethane brackets (with/without metal slots).
- Repeated torque testing (five cycles) using a testing machine and digital goniometer.
- Comparison with a control group of steel brackets; statistical analysis using one-way variance.
Main Results:
- Significant fluctuations in wire play and bracket elasticity were observed across bracket types.
- Polycarbonate bracket slots deformed after a single torque application, except for those with metal slots.
- All tested plastic brackets showed a significant loss of torque stability (5-28.5%) after one load cycle, averaging 17%.
Conclusions:
- Plastic brackets require material-specific torque values for effective tooth movement.
- Only plastic brackets incorporating a metal slot demonstrated suitability for clinical application compared to steel.
- Reinforcing polycarbonate or using polyurethane did not enhance torque stability; all plastic brackets lost stability after initial loading.
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