Force system evaluation of symmetrical beta-titanium T-loop springs preactivated by curvature and concentrated bends

Abstract

Introduction: The objective of this research was to compare the effect of preactivation on the force system of beta-titanium T-loop springs (TLSs). Methods: Twenty TLSs with dimensions of 6 x 10 mm, of 0.017 x 0.025-in beta-titanium alloy, were randomly divided into 2 groups according to their preactivation. By using a moment transducer coupled to a digital extensometer indicator adapted to a testing machine, the amounts of horizontal force and moment produced were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation in an interbracket distance of 23 mm. The moment-to-force ratio, the "neutral position" and the load-deflection ratio were also calculated. Results: TLSs preactivated by curvature delivered horizontal forces significantly lower than those preactivated by concentrated bends. No differences were found in relation to the moments produced throughout the deactivation of both groups. The moment-to-force ratios were systematically higher on the TLSs preactivated by curvature than those preactivated by concentrated bends, except on 5 mm of activation. Significant differences were found in the load-deflection rates and "neutral position." Conclusions: The TLSs preactivated by curvature delivered lower horizontal forces and higher moment-to-force and load-deflection ratios than did those preactivated by concentrated bends. (Am J Orthod Dentofacial Orthop 2011;140:e53-e58)