Force-Controlled Biomechanical Simulation of Orthodontic Tooth Movement with Torque Archwires Using HOSEA (Hexapod for Orthodontic Simulation, Evaluation and Analysis)

Abstract

This study aimed to investigate the dynamic behavior of different torque archwires for fixed orthodontic treatment using an automated, force-controlled biomechanical simulation system. A novel biomechanical simulation system (HOSEA) was used to simulate dynamic tooth movements and measure torque expression of four different archwire groups: 0.017″ x 0.025″ torque segmented archwires (TSA) with 30° torque bending, 0.018″ x 0.025″ TSA with 45° torque bending, 0.017″ x 0.025″ stainless steel (SS) archwires with 30° torque bending and 0.018″ x 0.025″ SS with 30° torque bending (n = 10/group) used with 0.022″ self-ligating brackets. The Kruskal-Wallis test was used for statistical analysis (p < 0.050). The 0.018″ x 0.025″ SS archwires produced the highest initial rotational torque moment (M_y) of -9.835 Nmm. The reduction in rotational moment per degree (M_y/R_y) was significantly lower for TSA compared to SS archwires (p < 0.001). TSA 0.018″ x 0.025″ was the only group in which all archwires induced a min. 10° rotation in the simulation. Collateral forces and moments, especially F_x, F_z and M_x, occurred during torque application. The measured forces and moments were within a suitable range for the application of palatal root torque to incisors for the 0.018″ x 0.025″ archwires. The 0.018″ x 0.025″ TSA reliably achieved at least 10° incisal rotation without reactivation.

Keywords: 3D measurement; biomechanics; force control; hexapod; orthodontics.

Figure 1

(a) Plaster model in the examination chamber of HOSEA; the force-torque sensor is attached to the anterior segment, while the posterior segment is connected to the moving Stewart platform. (b) Plaster model in the starting position, with superimposed coordinate system used for the measurements.

Figure 2

Graphs depicting rotational moments (Nmm) at the center of force in relation to the rotation of the segment (°). All measurements started at a rotational angle of 0° with an initial moment M_y (R_y = 0.1°). HOSEA rotates the posterior segment until My has come to an equilibrium position and rotation has stopped. Every colored curve corresponds to the measurement of one archwire. Each graph represents the archwires within a sample group.

Figure 3

Graphs depicting collateral forces F_x and F_z at the center of force in relation to the rotation of the segment (°). All measurements started at a rotational angle of 0° with an initial moment My (R_y = 0.1°). Every colored curve corresponds to the measurement of one archwire. Each graph represents the archwires within a sample group.