Background This study compared the frictional force resulting from the bracket/archwire interface and the stress at the root/periodontal ligament/bone interface, between passive self-ligating brackets and conventionally ligated brackets, during the space closure stage. Material and Methods A cone beam tomography was taken to a female patient that required extraction of upper first premolars and passive self-ligating system; three months after its activation, a cone beam tomography was taken again. The designs of the maxillary bone and the entire system were possible through tomography images and stereomicroscopic photographs. Validation of the Finite Element Method (FEM) was achieved comparing the amount of movement seen through tomography images and the FEM. Space closure was simulated for each system through the FEM and a comparison was made between the frictional force at the bracket/archwire interface, and the root/periodontal ligament/bone interface. Results The most significant representation of frictional force at bracket/archwire interface and bone stress was found at the conventionally ligated system, while the passive self-ligating system accounted for the highest distribution of stress over the root. Conclusions The FEM is an accurate tool used to quantify frictional force and stress concentration during the orthodontic closure. The passive self-ligating system was seen less frictional during the closure state compared to conventional brackets. Key words: Friction, orthodontic bracket, finite element analysis.
βTi T-type loops are a frictionless, efficient alternative for extraction space closure. Changes in the upper horizontal portion of T-type loops to improve their mechanical behavior have been proposed, but differences in their biomechanical characteristics have not been well described. This stu dy analyzed the biomechanical differences among three T-type loops with differential bends in their upper horizontal portion. Ninety loops (0.017"x0.025" βTi) were bent and randomly divided in 3 groups according to the form of their upper horizontal portion (T [straight], M [convex], and C-loops [concave]), to evaluate force characteristics up to 6 mm of activation. Stiffness, maximum horizontal loads, total loop moments, and moment-to-force ratios were obtained. Nonparametric statistical analyses were used to test differences among groups. M-loops demonstrated lower force than T-and C-loops, and higher total loop moment than T-loops. A significant increase in M-loop moment-to-force ratio compared with T-or C-loops was obtained. C-and T-loops did not demonstrate significant differences in moment-to-force ratio between them. The convex upper bend in M-loops produced an increased total loop moment compared with T-loops. M-loops demonstrated moment-to-force values slightly higher than translation values, while the other loops reported only controlled inclination values at 6 mm of activation. M-loops are ideal when a higher control of root movement is indicated since the beginning of dental retraction in segmented arch mechanics.
Introducción y objetivo: La fricción en la ortodoncia se produce por contacto directo entre el bracket, el alambre y la ligadura. La fricción reduce la eficiencia en los tratamientos de ortodoncia. Esta investigación comparó la resistencia a la fricción entre los brackets cerámicos convencionales y los brackets cerámicos de autoligado pasivos utilizando un método de elementos finitos (MEF). Materiales y métodos: Se realizó un total de 810 deslizamientos, combinando brackets cerámicos convencionales y autoligados, y alambres de ortodoncia de acero inoxidable, níquel-titanio y de la aleación β-titanio de 0.016 pulgadas, 0.017x0.025 pulgadas y 0.019 x0.025 pulgadas. La media máxima de resistencia a la fricción estática (MRF) se comparó entre las diferentes combinaciones de brackets, alambre, ligadura y angulación del bracket de 0 °, 7 ° y 13 °. Resultados: Las variables con el comportamiento de fricción más alto fueron 13 °, aleación β titanio, 0.017x0.025 pulgadas, y brackets cerámicos convencionales con ligaduras elásticas. Conclusión: MEF es una alternativa adecuada para la predicción de la MRF en varias combinaciones de brackets, alambres, ligaduras y angulaciones. El método permitió definir una menor resistencia a la fricción para los brackets de autoligado, así como una relación directa entre el aumento del ángulo y el área de contacto entre el bracket y el alambre, con valores más altos de resistencia al deslizamiento. Se estableció que un alambre de mayor calibre no implica un área de mayor contacto con el bracket.
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