M/F Changes after T-loop Upper Horizontal Bending in Segmented Arch Mechanics

Abstract

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.

Finite element analysis of archwire parameters and activation forces on the M/F ratio of vertical, L- and T-loops

“…In other words, the higher the loop height, the larger the M/F ratio generated by the loop. This finding was consistent with those of other studies [13,18,[26][27][28]. Ribeiro et al [13] demonstrated that the M/F ratio increased with increases in the loop height of composite nickel-titanium T-loops.…”

“…For minor changes in the loop height, the conversion of conventional T-loops into M-loops would increase the M/F ratio. Muñoz-Rendón [27] reported that the convex upper bend of M-loops produced an increased total loop moment compared with T-loops because the upper convex bending increased the total loop height. Moreover, Burstone and Koenig [18] reported that the height of the loop matters more than the length.…”