Effects of height and overactivation on a composite nickel-titanium T-loop

Abstract

Objective: Evaluate the effect of height and overactivation on the force system produced by composite nickel-titanium T-loops. Material and Methods: Forty nickel-titanium/stainless steel (SS) T-loops were divided into four groups according to height (7 or 6 mm) and activation/deactivation protocol (7 mm or 7 mm with 2 mm of overactivation). An Orthodontic Force Tester recorded the y-axis force and the x-axis moment produced for each 0.5 mm of deactivation, while the moment(x)-to-force(y) (M/F) ratio was calculated. The data were analyzed by three analyses of variance of repeated measures to detect differences and interactions between height and protocol on the three variables. Results: T-loops with a height of 6 mm produced higher forces (2.97 N vs. 2.66 N) than those of 7 mm. The moments were similar, whereas the M/F was larger for the 7-mm loops (5.76 mm vs. 4.92 mm). The conventional activation produced higher forces (2.99 N vs. 2.64 N), higher moments (16.2 Nmm vs. 13.59 Nmm) but the same M/F. The M/F showed an interaction with deactivation. Conclusion: The 6-mm-high T-loops produced higher forces, but lower M/F. The conventional protocol produced higher forces and moments. The M/F ratio was similar for both protocols, but overactivation produced a nearly constant M/F throughout deactivation. The use of a 7-mm-high overactivated segmented nickel-titanium loop might improve the performance of orthodontic space closure.

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

“…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.…”

“…Clearly, rigorous engineering approaches are needed to study the mechanical properties of loops and identify the dominant design factors that can be used to control loop behavior. Several studies [10][11][12][13][14] examined the ability of a loop design to generate various M/F ratios, especially a sufficiently high M/ F ratio for tooth translation and the loop characteristics that determine this ratio.…”