Influence of normal forces on the frictional behavior in tribological systems made of different bracket types and wire dimensions

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

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 (My) of -9.835 Nmm. The reduction in rotational moment per degree (My/Ry) 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 Fx, Fz and Mx, 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.

Friction Force Adjustment by an Innovative Covering System Applied with Superelastic NiTi Brackets and Wires-An In-Vitro Study

The aim of this study was the investigation of polymeric coverings to adjust frictional forces between V-shaped wires and brackets, both made of superelastic NiTi. Adjustment of frictional forces is relevant for certain stages during orthodontic therapy. Coverings able to generate frictional forces when assembled to such brackets are additively manufactured. Six different internal widths of coverings were examined in three different environments: dry condition at room temperature (RT) or body temperature (BT), or artificial saliva (AS) at RT. The different coverings significantly affected the frictional forces for all media (p < 0.001). A correlation between internal width of the covering and resulting frictional forces was found. BT and dry environment showed the lowest friction forces for all samples. The highest force was found for two covering types at RT in AS, while the remaining four covering types showed the highest values in dry environment (p < 0.001). Friction could, therefore, be adjusted by variation of bracket covering clipped onto brackets, which is useful for orthodontic therapy. Coverings delivering higher friction provide dental anchorage, while coverings with lower friction can be used for tooth movement or purely esthetic reasons. It was shown that the variation of covering width may be used for adjustment of frictional forces.