The Effect of Wire Fixation Methods on the Measured Force Systems of a T-Loop Orthodontic Spring

Abstract

Ideal orthodontic springs are able to provide a controlled moment-to-force (M/F) ratio and a low load deflection rate. A great deal of research has gone into describing force systems generated by orthodontic springs. Most studies investigating the force system generated by T-loops have used rigid fixation for the spring ends. This is practical for laboratory studies, but it does not truly represent clinical situations in which orthodontic brackets are used to anchor spring ends. Results from laboratory studies have been applied to clinical situations without regard to what effect, if any, the method of end fixation may have. It is the goal of this study to determine the effects of spring fixation on generated force systems. The springs were held by rigid fixation and bracket ligation with either elastomeric or steel ligature ties. Comparison of these fixation methods was made by testing T-loops of different dimensions, with and without heat treatment at various activation distances. In theory, the wire is ligated rigidly against the bracket, so that the combination acts as a single unit by rigid fixation. Thus, there should be no difference between the generated force systems when spring ends are held by rigid fixation, or when they are held in place with orthodontic brackets and ligated by either elastomeric or steel ligature ties. However, the results indicate that are significant differences among the methods of fixation for each spring variation and heat treatment. The rigid fixation method consistently produced smaller moments and M/F ratios for all springs with every activation and heat treatment combination.