Mechanical performance of tear-drop loops and tear-drop loops with helix used for space closure in Orthodontics

Abstract

The present study evaluated the force systems produced by tear-drop loops and tear-drop loops with helix, with employment of different transverse sections (0.017"x0.025" and 0.019"x0.025") and different gable bend intensities (0° and 40°). For that purpose, 40 loops for space closure were submitted to mechanical testing, which were centralized in a space of 2mm. The magnitudes of the horizontal force, load/deflection ratio and moment were quantified with a moment transducer connected to a digital indicator for extensometry adapted to an Instron universal testing machine. The loops were submitted to a total activation of 3.0 millimeters, with the values quantified in each 1.0 millimeter of distention. In the statistical analysis of the data achieved, it was employed the Variance Analysis and the Tukey Test for Multiple Comparisons, at a significance level of 5%. The results indicated that the insertion of gable bends in the closure loops resulted in increased magnitudes of moment/force ratio, horizontal force and load/deflection ratio. The increase in the transverse section of the wire used for confection of the closure loop resulted in higher values of horizontal force and load/deflection ratio, with little effect in the moment/force ratio. Analyzing the force systems generated by the tear-drop loop and tear-drop loop with helix, that means the horizontal force, load/deflection ratio and moment/force ratio, it was verified that tested loops produced values of horizontal force adequate to realize tooth movement, but inadequate moment/force ratio to control root movement during space closure.