Bending stiffness of two aesthetic orthodontic archwires: An in vitro comparative study

Abstract

The aims of the study were to quantify the transverse stiffness of two aesthetic orthodontic archwires (0.018 inch Teflon-coated stainless steel and 0.017 inch Optiflex) in a simulated clinical setting and to assess the influence of deflection direction on the bending stiffness. The aesthetic archwires were randomly divided into three equal groups: group 1, lingual deflection; group 2, labial deflection; and group 3, occlusal deflection. Each group consisted of six archwires of the same type. The control group consisting of eighteen 0.014 inch stainless steel archwires were also subjected to the same grouping. A total of 54 archwires were tested in the study. The deflection of the archwires was measured with a travelling microscope and the load measured with a calibrated strain gauge ring transducer. The mean stiffnesses of the archwires in the lingual, labial and occlusal deflection groups were found to be 2.9, 0.8 and 2.5 mN/mm respectively for 0.017 inch Optiflex (r = 0.9, P < 0.001), 13.2, 10.5 and 24.5 mN/mm respectively for 0.018 inch Teflon-coated stainless steel (r = 0.9, P < 0.001) and 26.6, 16.4 and 32.3 mN/mm respectively for the control (r = 0.9, P < 0.001). Springback was found to be poor for Optiflex and the archwire remained bent upon deactivation. ANOVA showed that the influence of arch curvature on the bending stiffness was significantly different for Optiflex (P < 0.05), Teflon-coated stainless steel (P < 0.005) and the control group (P < 0.005). Stiffness for the Teflon-coated archwire was found to be higher and more in line with the stiffness for the control. Both the Teflon-coated and stainless steel archwires displayed good springback property. However, Optiflex was found to have low stiffness and resilience. Owing to the poor springback, the clinical efficacy of Optiflex is probably limited.