title: Torquing an upper central incisor with aligners--acting forces and biomechanical principles.
abstract: The forces delivered by aligners during torquing have still not been investigated. The purpose of this study was to measure the forces delivered to an upper central incisor during torquing with three different materials of the same thickness, and to describe the biomechanical principles of torquing with aligners. Five identical appliances were manufactured from each of three materials, all with a thickness of 1.0 mm (Ideal Clear®, Erkodur®, and Biolon®). An upper central incisor, as part of the measuring device, was torqued in defined steps in the vestibular and palatal directions with the respective appliance in place. For statistical analysis, the resulting forces, Fx (forces acting in the palatal and facial directions) and Fz (intrusive force as a side-effect) at a displacement of ±0.15 and ±0.8 mm from the tooth at the gingival margin were calculated. The mean Fx forces for ±0.15 mm displacement ranged from -1.89 N [standard deviation (SD) 0.48] to 0.11 N (SD 0.1). The mean Fz forces were between -0.97 N (SD 0.57) and -0.07 N (SD 0.22). The highest intrusive forces were measured during palatal displacement of the measuring tooth. An influence of direction of displacement on the levels of force was observed, especially for Fz at the greater displacement of ±0.8 mm. In relation to the intended amount of root movement during torquing, aligners tend to 'lift up' and therefore no effective force couple can be established for further root control. The force delivery properties are also influenced by the material used and the shape of the tooth.
authors.affiliation: Department of Orthodontics, Dental Clinic, Georg-August-University of Göttingen, Germany. weahahn@aol.com
authors.forename: Wolfram
authors.initials: W
authors.lastname: Hahn
authors.forename: Antonia
authors.initials: A
authors.lastname: Zapf
authors.forename: Henning
authors.initials: H
authors.lastname: Dathe
authors.forename: Julia
authors.initials: J
authors.lastname: Fialka-Fricke
authors.forename: Susanne
authors.initials: S
authors.lastname: Fricke-Zech
authors.forename: Rudolf
authors.initials: R
authors.lastname: Gruber
authors.forename: Dietmar
authors.initials: D
authors.lastname: Kubein-Meesenburg
authors.forename: Reza
authors.initials: R
authors.lastname: Sadat-Khonsari
mesh_terms: D000180:Acrylic Resins; D001696:Biomechanical Phenomena; D003799:Dental Stress Analysis; D006801:Humans; D007180:Incisor / Q000473:pathology*; D008437:Maxilla; D016382:Orthodontic Appliance Design; D009968:Orthodontic Appliances, Removable; D018709:Statistics, Nonparametric; D014087:Tooth Movement Techniques / Q000295:instrumentation*; D019415:Torque
chemical_list: D000180:Acrylic Resins