Effect of the gable bends on the force system of T-loop orthodontic springs after activation: a numerical–experimental study

Abstract

The purposes of this study were to evaluate the effects of different preactivation bends on the force system and the mechanical stresses of beta-titanium T-loop orthodontic springs. A tridimensional T-loop spring finite element model was built aiming to obtain reactive forces and moments in the three directions (x, y and z) as well as the moment–force ratios (M/F) for the sagittal and occlusal planes considering different gable bends. Using a transducer designed to measure forces in the x- and y-axis and moment around the z-axis, experimental tests were performed to validate the numerical analysis. It was observed that Fx increases as the angle between extremities increases. The Fx magnitude changed from 0.2 to 2.0 N. Fy forces presented very low magnitude while in z direction they were null. In the sagittal plane, decreasing the gable bends increases the M/F ratio. On the other hand, in the occlusal plane, no change in the M/F ratio values was observed with the variation of the gable bends. The results obtained from the analyses showed that the M/F ratio presented different values because of different preactivation bends formed between alpha and beta extremities, consequently different types of dental movement can be produced. In the occlusal plane, no movement tendency was observed while in the sagittal plane there was a movement tendency to produce uncontrolled tipping, controlled tipping, translation and finally root correction. Translation tendency was observed during deactivation starting at 5.0 mm without crown rotation.