Verification of mechanical load generated by functional orthodontic appliances.

Functional appliances are widely used for promoting mandibular growth by utilizing a construction bite position. We aimed to measure the mechanical load generated by movement of functional appliances and determine the factors influencing this load. Thirteen patients aged 8-12 years were selected for the study, and the load was measured using a previously developed measurement device. To investigate the factors affecting the load, the temporomandibular joint morphology and muscles related to the mandible were examined using cone-beam computed tomography. The standard regression coefficients of the factors affecting the load per millimeter of movement distance were 0.64 and 0.66 for (a) the inclination of the articular eminence and (b) the angle between occlusal plane and posterior temporalis, respectively. Measurement of the occlusal plane to the posterior temporalis and the inclination of the articular eminence were significantly different (p < 0.05). The angle of inclination of the articular eminence emerged as a strong influencing factor. Similarly, the influence of measurements from the occlusal plane to the posterior temporalis was considerable since the posterior temporalis muscle is the most active when the mandible is extended forward. We also found a possible relationship between the occlusal force and load at the construction bite position. To our knowledge, this is the first study to determine the actual load associated with the angle of the temporalis muscle to the occlusal plane, inclination angle of the articular eminence, angle between the occlusal plane and the Frankfort plane, and the angle between the geniohyoid muscle and the occlusal plane. Therefore, mechanical considerations need to be more accurate to facilitate safe orthodontic treatment.

Mechanical Bed for Investigating Sleep-Inducing Vibration

In running cars or trains, passengers often feel sleepy. Our study focuses on this physiological phenomenon. If a machine can reproduce this phenomenon, it is feasible to put a person, such as an insomnia patient or an infant, to sleep without any harmful effects. The results of our previous study suggest that low-frequency vibration induces sleep. This report describes a new mechanical bed for inducing sleep and discusses the effects of different vibration conditions. The new bed has two active DOFs in the vertical and horizontal directions to examine the anisotropy of sensation. The bed includes three main parts: a vertical driver unit, a horizontal driver unit, and a unique 2-DOF counterweight system to reduce driving force and noise. With regard to motion accuracy, the maximum motion error in the vertical direction lifting 75 kg load was only 0.06 mm with a 5.0 mm amplitude of a 0.5 Hz sinusoidal wave. The results of excitation experiments with 10 subjects showed a significant difference in sleep latency between the conditions with vibration and without vibration. Furthermore, the average latency with insensible vibration (amplitude = 2.4 mm) was shorter than that with sensible vibration (amplitude = 7.5 mm). These results suggest the ability of appropriate vibration to induce sleep.

Mechanical Bed for Investigating Sleep-Inducing Vibration.

In running cars or trains, passengers often feel sleepy. Our study focuses on this physiological phenomenon. If a machine can reproduce this phenomenon, it is feasible to put a person, such as an insomnia patient or an infant, to sleep without any harmful effects. The results of our previous study suggest that low-frequency vibration induces sleep. This report describes a new mechanical bed for inducing sleep and discusses the effects of different vibration conditions. The new bed has two active DOFs in the vertical and horizontal directions to examine the anisotropy of sensation. The bed includes three main parts: a vertical driver unit, a horizontal driver unit, and a unique 2-DOF counterweight system to reduce driving force and noise. With regard to motion accuracy, the maximum motion error in the vertical direction lifting 75 kg load was only 0.06 mm with a 5.0 mm amplitude of a 0.5 Hz sinusoidal wave. The results of excitation experiments with 10 subjects showed a significant difference in sleep latency between the conditions with vibration and without vibration. Furthermore, the average latency with insensible vibration (amplitude = 2.4 mm) was shorter than that with sensible vibration (amplitude = 7.5 mm). These results suggest the ability of appropriate vibration to induce sleep.

Development of a measurement system for the mechanical load of functional appliances.

Devices called functional appliances are commonly used in orthodontics for treating maxillary protrusion. These devices mechanically force the mandible forward to apply traction force to the mandibular condyle. This promotes cartilaginous growth in the small mandible. However, no studies have clarified how much traction force is applied to the mandibular condyle. Moreover, it remains unknown as to how anatomical characteristics affect this traction force. Therefore, in this study, we developed a device for measuring the amount of force generated while individual patients wore functional appliances, and we investigated the relationship between forces with structures surrounding the mandibular condyle. We compared traction force values with cone-beam computed tomography image data in eight subjects. The functional appliance resulted in a traction force of 339-1477gf/mm, with a mean value of 196.5gf/mm for the elastic modulus of the mandible. A comparison with cone-beam computed tomography image data suggested that the mandibular traction force was affected by the mandibular condyle and shape of the articular eminence. This method can contribute to discovering efficient treatment techniques more suited to individual patients.

Active joint mechanism driven by multiple actuators made of flexible bags: a proposal of dual structural actuator.

An actuator is required to change its speed and force depending on the situation. Using multiple actuators for one driving axis is one of the possible solutions; however, there is an associated problem of output power matching. This study proposes a new active joint mechanism using multiple actuators. Because the actuator is made of a flexible bag, it does not interfere with other actuators when it is depressurized. The proposed joint achieved coordinated motion of multiple actuators. This report also discusses a new actuator which has dual cylindrical structure. The cylinders are composed of flexible bags with different diameters. The joint torque is estimated based on the following factors: empirical formula for the flexible actuator torque, geometric relationship between the joint and the actuator, and the principle of virtual work. The prototype joint mechanism achieves coordinated motion of multiple actuators for one axis. With this motion, small inner actuator contributes high speed motion, whereas large outer actuator generates high torque. The performance of the prototype joint is examined by speed and torque measurements. The joint showed about 30% efficiency at 2.0 Nm load torque under 0.15 MPa air input.