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

Inclination Changes in Incisors During Orthodontic Treatment with Passive Self-Ligating Brackets

Background: Correct inclination of the incisors is crucial for function and occlusion. The aim of this retrospective cephalometric study was to investigate the effect of orthodontic treatment with passive self-ligating (SL) brackets on the incisor inclination compared to untreated controls. Methods: This study evaluated an orthodontic treatment group (n = 30, Ø13.4 years, ANB Ø2.3°) before (T1) and after (T2) orthodontic therapy with passive SL-brackets (MBT prescription, 0.022″ slot) by one experienced orthodontist. The control group was matched according to age and sex (n = 30, Ø13.3 years, ANB Ø2.5°). The incisor inclination was evaluated digitally using cephalometric lateral radiographs. Results: The cephalometric evaluation showed a significant incisor proclination during orthodontic treatment with SL brackets. The upper incisors proclined by +3.8° (U1-PP) and +3.7° (U1-SN) and the lower incisors proclined by +4.4° (L1-MP). The control group presented a reclination of the upper incisors by -1.4° (U1-PP) and -0.6° (U1-SN) and the lower incisors by -0.4° (L1-MP). The clinically relevant protrusion effect during orthodontic treatment with SL brackets summed up to +5.2° (U1-PP), and +4.3° (U1-SN) for the upper incisors (+2.0°/year, +1.6°/year) as well as +4.8° (L1-MP) for the lower incisors (+1.6°/year) compared to controls. Sex-specific differences were found. Males showed a greater proclination of the upper incisors by +5.3° (U1-PP) and +5.9° (U1-SN) compared to females in the treatment group. Conclusions: Orthodontic treatment with SL brackets results in protrusion of the upper and lower incisors by +5° compared to controls. These findings must be considered in orthodontic treatment planning according to initial diagnostics.

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.