Torque resistance of different stainless steel wires commonly used for fixed retainers in orthodontics.
OBJECTIVE
Movements of teeth splinted by fixed retention wires after orthodontic treatment have been observed. The aetiological factors for these movements are unknown. The aim of this in vitro study was to compare the resistance to torque of different stainless steel wires commonly used for fixed retainers in orthodontics.


METHODS
Torquing moments acting on a retainer wire were measured in a mechanical force testing system by applying buccal crown torque to an upper lateral incisor in both a 3-teeth and in a 2-teeth setup. Seven stainless steel wires with different shape, type (plain, braided, coaxial, or chain) and dimensions were selected for this study.


RESULTS
For a torquing angle of 16.2° in the 3-teeth setup torsion moments can vary between 390 cNmm and 3299 cNmm depending on the retainer wire. For the 2-teeth setup the torsion moments are much smaller. Exposure to the flame of a butane-gas torch for 10 seconds to anneal the wire reduces the stiffness of the retainer wire.


CONCLUSIONS
Clinicians must select wires for fixed retainers very carefully since the difference in resistance to torque is large. A high level of torque control can be achieved with a plain 0.016 × 0.016-inch or a braided 0.016 × 0.022-inch stainless steel wire. A tooth attached by a retainer wire to only one neighbouring tooth is less resistant to torque than a tooth connected to two neighbouring teeth. Annealing a retainer wire with a flame reduces the stiffness of the wire markedly and can lead to a non-uniform and non-reproducible effect.
a Department of Orthodontics and Pediatric Dentistry , University of Basel , Basel , Switzerland.
Dario T
DT
Arnold
a Department of Orthodontics and Pediatric Dentistry , University of Basel , Basel , Switzerland.|b Section of Orthodontics, Department of Dentistry , Aarhus University , Aarhus , Denmark.
Michel
M
Dalstra
a Department of Orthodontics and Pediatric Dentistry , University of Basel , Basel , Switzerland.
Carlalberta
C
Verna
D006801:Humans; D016382:Orthodontic Appliance Design; D018704:Orthodontic Retainers; D009969:Orthodontic Wires; D013193:Stainless Steel; D019415:Torque
D013193:Stainless Steel
Orthodontic wire retainer; annealing; resistance to torque; unexpected tooth movements