title: Torque transmission between square wire and bracket as a function of measurement, form and hardness parameters.
abstract: The aim of the study was to investigate the influence of cross section, edge geometry and structural hardness on torque transmission between square wire and bracket. For this purpose, 5 different brands of stainless steel square wire in 3 dimensions (0.016" x 0.016", 0.016" x 0.022" and 0.017" x 0.025") were inserted into edgewise brackets with a slot size of 0.018" and loaded with different torques (1 and 3 Ncm). The slot and wire geometries were analyzed by computer on ground specimens before and after loading. In addition, the Vickers hardness and micro-hardness of the unstressed and stressed metal surfaces were determined. While the slot size was very accurately maintained, the wire dimensions deviated downwards by an average of 10%. Torque transmission led to notching and bending-up phenomena on the bracket slot flanks. A torque loading of 3 Ncm increased the torque play of 0.016" x 0.022" wires by 3.6 degrees, and of 0.017" x 0.025" wires by 3.7 degrees. In the case of 0.016" x 0.016" wires, an effective torque transmission was no longer possible. The average Vickers hardness of the wires was 533 kp/mm2, and that of the brackets 145 kp/mm2. The micro-hardness in the deformation area of stressed internal slot walls increased with increasing load transmission from 204 to 338 kp/mm2. As a result of excessively small wire dimensions and plastic deformation of the brackets, a relatively large torque play occurs. Deformation and notching in the area of the internal slot walls are inconsistent with demands for recycling brackets. A standardization of bracket wire systems stating the actual torque play would be desirable.
authors.affiliation: Department of Orthodontics, University of Kiel, Germany. fi-br@kfo-zmk.uni-kiel.de
authors.forename: H
authors.initials: H
authors.lastname: Fischer-Brandies
authors.forename: W
authors.initials: W
authors.lastname: Orthuber
authors.forename: M
authors.initials: M
authors.lastname: Es-Souni
authors.forename: S
authors.initials: S
authors.lastname: Meyer
mesh_terms: D006244:Hardness; D006245:Hardness Tests / Q000295:instrumentation / Q000379:methods; D006801:Humans; D008422:Materials Testing / Q000379:methods / Q000706:statistics & numerical data; D016382:Orthodontic Appliance Design / Q000706:statistics & numerical data; D016910:Orthodontic Brackets / Q000706:statistics & numerical data; D009969:Orthodontic Wires / Q000706:statistics & numerical data; D019415:Torque