Experimental evaluation of orthodontic bracket slot deformation to simulated torque

In orthodontic fixed appliance therapy, the archwire torque used to refine the teeth position during the treatment imparts significant forces inside the bracket slot. The objective of this study was to measure the torque relevant bracket slot deformation in Stainless Steel (SS) brackets during various degree of archwire twist. Standard edgewise brackets 0.018-inch (in.)/0.022-in. each 20 no. and 0.016 × 0.022, 0.017 × 0.025, 0.019 × 0.025, and 0.021 × 0.025 in. archwires each 10 no. were used. A novel experimental setup consisting of loading fixture and torque key mounted on a Vision Measuring System (VMS) were used to measure the brackets slot deformation. The Top Slot and Middle Slot Deformations (TSD and MSD) of the brackets for 35° angle of twist in 0.016 × 0.022 in. archwire in 0.018-in. slot, 0.019 × 0.025 in. archwire in 0.022-in. slot and for 30° angle of twist in 0.017 × 0.025 in. archwire in 0.018-in. slot and 0.021 × 0.025 in. archwire in 0.022-in. slot were measured. Results showed that the mean TSD and MSD were higher when the archwire size, the slot size and the angle of twist were greater. In the evaluated bracket-archwire combinations, the TSD were higher than MSD and the bracket slots were elastically deformed within the clinically required 35° angle of twist in the archwire. Clinicians should be aware of this torque relevant bracket slot deformation which might be a factor for torque loss and suitably incorporate archwire angle of twist.