Three-dimensional analysis of an orthodontic delta spring

INTRODUCTION: The purpose of this study was to analyze the force system, moment-force ratios (M/F) and von Mises stresses in an orthodontic delta spring using a 3D finite element model. The M/F ratio produced by an orthodontic spring is related to the different types of tooth movement that are likely to occur in the sagittal and occlusal planes. METHODS: Analyses were performed using a 3D finite element model, and a data acquisition system was used to validate the numerical results. RESULTS: Reactive forces between 0.0 and 2.0 N were observed along the x-axis, while null values were observed along the y- and z-axes. The maximum activation that ensured geometric stability and mechanical stresses below the elastic limit of the material was 10.0 mm. CONCLUSION: The results indicate that a delta spring can provide (i) uncontrolled tipping for activation of less than 1.0 mm; (ii) controlled counterclockwise tipping for activation between 1.0 and 4.5 mm; (iii) translation for activation between 4.5 and 5.0 mm; and (iv) controlled clockwise tipping in the sagittal plane for activation between 5.0 and 10.0 mm. No tooth movement was observed in the occlusal plane for the M/F ratios observed.

ELECTROMYOGRAM PATTERNS DURING SUSTAINED LOW-LEVEL PLANTAR FLEXIONS AND CHANGES IN BLOOD FLOW FOR "ALTERNATE ACTIVITY" AMONG THE TRICEPS SURAE MUSCLES / 体力科学

Several studies have described "Alternate activity", in which individual muscles of the synergistic muscle group alternate between high activity and silent periods, and rotate in a complementary pattern to maintain constant torque, during sustained low-level contractions. The purpose of this study was to investigate the physiological property of alternate activity among the synergists. Eight human subjects performed static contractions at an ankle joint angle of 110° plantar flexion at 10% maximal voluntary contraction (MVC) for 120 min. Simultaneously, a surface electromyogram (EMG) was recorded of the triceps surae muscles. Doppler ultrasound techniques were used to measure blood velocity and the arterial diameter of the popliteal artery during exercise. Maximal torque at MVC and mean EMG (mEMG) level decreased significantly after sustained isometric low-level contractions, but there was no significant difference in the mEMG/maximal force ratio of triceps surae muscles, which is thought to indicate peripheral fatigue between pre- and post-exercise. Throughout the "Alternate activity", arterial diameter and pulse rate did not change, but blood flow significantly increased (p<0.001) depending on an increase in blood velocity. These results suggest that "Alternate activity" among the triceps surae muscles may be one mechanism that functions either to decrease or to postpone peripheral fatigue during sustained low-level contraction.

The reaction of bone regenerate to the various force ratio and periods on distraction osteogenesis with combined distraction force and compression force

Physical properties of various brands of elastomeric chains / 대한치과교정학회지

Forces needed for orthodontic tooth movement are obtained from various appliances such as orthodontic wires or elastic rubber. Orthodontic elastic rubber is widely used clinically, but permanent deformation and force decay may occur from the environmental changes, time of clinical use and the extent of the stertch, making the prediction of force being applied difficult. The present study examined and compared the changes in residual force between three brands of elastomertc chains (Ormco : Generation II Power Chains ; brand A, RMO : Energy-Chain ; brand B, Unitek : Alastik ; brand C) under various environmental conditions, amout of inital force, types of elastomer and the rate of extension. The characteristic physical properies of the elastomeric chains were as follows. 1. In all three brands, the residual force ratio was largest when the chains were stored in air, with no difference between water and saliva. 2. In all three brands, after 24 hours, there was no statistical difference in residual force ratio according to the initial force level. 3. In Brand A and B, the presence of filament had no correlation with the residual force ratio. In Brand C force decay was more severe when the chain contained filament. 4. In each brand, rate of extension had no effect on residual force ratio. 5. Brand B showed relatively higher residual force ratio compared to other brands.