Finite Element Analysis of Three Dimensional Force System from Beta Titanium and Steel Preactivated Retraction Springs

The aim of this study was to investigate the effects and interactions of first– and second– order preactivation bends on three dimensional force system of steel and beta titanium canine retraction springs.Method and materials: In a non- linear finite element analysis, three retraction springs including, vertical loop, vertical helical loop and T– loop were studied. All combinations of first-order bend (0, 20, 40 and 60 degrees), second-order bend (0, 20 and 40 degrees) and wire material (stainless steel, beta titanium) were applied to each design. All appliances activated incrementaly to reach elastic limit in 0.05 mm steps. Moment/ force ratios (in occlusal and sagital plan) and load/ deflection rate of appliances were measured using ABAQUS, V6.8 and CATIA, V5.13 softwares. It was found that the second–order bend can somewhat reduce moment/ force ratio in occlusal plan but first order bend have no effect on moment/ force ratio in sagital plan. The addition of helix into the vertical loop reduced load deflection rate of spring but did little to alter the moment/ force ratios of spring. First and second–order preactivation of retraction springs produced the desired effects, without significant interfering with each other. Helices added to the vertical loop may improve some mechanical characteristics of retraction springs.