Deformation and warping of the bracket slot in select self-ligating orthodontic brackets due to an applied third order torque

Abstract

To measure the plastic deformation of three different self-ligated brackets as a result of third order torque by analysing slot dimensions and determine its impact on torque play. Three different self-ligating orthodontic brackets (0·022-inch slot) were investigated: Damon Q®, In-Ovation R®, and Speed® (30 per group). A digital SLR camera coupled to a microscope was used to capture images of the slot profile of each bracket before and after torquing. Each bracket was torqued to 63° in the same manner using a 0·019×0·025-inch SS wire. The mean change in slot height as measured at the top of the slot was 0·013 mm (SD 0·020), 0·007 mm (SD 0·010) and 0·070 mm (SD 0·03) for Damon Q®, In-Ovation R® and Speed®, respectively. Slot taper increased 0·75° (SD 0·96), 0·41° (SD 1·05) and 9·30° (SD 4·24), respectively. Increase in torque play was calculated to be 0·9, 0·6 and 7·7° respectively, as calculated using the novel formula presented in this study. Damon Q® and In-Ovation R® maintain high levels of linearity in the shape of the slot walls and experience small, but significant amounts of plastic deformation that are physically insignificant. Speed® demonstrates the most plastic deformation with visually identifiable warping in the bracket slot.