Displacement and stress distribution of Kilroy spring and nickel-titanium closed-coil spring during traction of palatally impacted canine: A 3-dimensional finite element analysis

Objective: To compare the stress distribution and initial displacements during traction of palatally impacted canine between Kilroy and nickel-titanium (NiTi) closed-coil springs by means of the finite element analysis.

Setting and sample population: A finite element method analysis of two traction methods for a maxillary impacted canine.

Materials and methods: The corresponding periodontal ligaments (PDLs), brackets, molar tubes and a 0.019 × 0.025-in base stainless-steel (SS) wire were modelled and imported to ANSYS SpaceClaim version 2020 R1. Traction was simulated under two different set-ups with equal force magnitude (60 g); (1) the Kilroy spring, which is made of 0.016-inch SS, and (2) the NiTi closed -coil spring. Von Mises stress distributions and initial displacements of the maxillary teeth were analysed.

Results: In both mechanics, while the highest stress was seen on the impacted canine (Kilroy, 10.41 kPa; NiTi closed-coil, 5.27 kPa), the stress distribution decreased as the distance from the impacted canine increased. The Kilroy spring showed a greater total displacement (465.60 μm) on the impacted canine. The higher stresses on the adjacent lateral (5.29 kPa) and premolar (6.41 kPa) occurred with the Kilroy spring.

Conclusions: The Kilroy spring yielded higher stresses than the NiTi closed-coil spring on the impacted canine and the adjacent teeth. The difference between distribution of the stresses over the impacted canine induced greater displacement with the Kilroy spring, particularly in the vertical direction.