Experimental studies for the progressive assessment of stress distributions on orthodontic archwire

This paper presents experimental studies to examine effect of crowding stages on stress distributions on orthodontic archwire using loading tests and 2D photogrammetry technique. Three specimens representing crowding II, crowding I, and alignment stage were fabricated based on a 3D images of upper teeth. Engaged NiTi archwire is loaded with weights to induce deformation, and 2D photogrammetry technique was used to loaded wire and curvature change of the engaged wire from the captured images. Axial and flexural stresses were obtained, which were used to calculate von Mises stress distributions along the wire. The results show that the averaged von Mises stress of archwire was released in about 10% when the alignment of teeth changes from crowding II to I and crowding I to alignment. Comparing all three stages, it was common that flexural stresses were much larger than the axial stresses. In addition, the wire stresses were concentrated more on molar teeth area due to anchorage effect, regardless of crowding stage. This study shows not only how stresses were distributed along the wire but also how stress distributions on wire change as orthodontic treatment proceeded, which can be used to improve effectiveness of treatment and develop wire design.