Ultrasound Imaging Characterization of Soft Tissue Dynamics of the Seated Human Body

To characterize the dynamics of internal soft organs and external anatomical structures, this paper presents a system that combines medical ultrasound imaging with an optical tracker and a vertical exciter that imparts whole-body vibrations on seated subjects. The spatial and temporal accuracy of the system was validated using a phantom with calibrated internal structures, resulting in 0.224 mm maximum root-mean-square (r.m.s.) position error and 13 ms maximum synchronization error between sensors. In addition to the dynamics of the head and sternum, stomach dynamics were characterized by extracting the centroid of the stomach from the ultrasound images. The system was used to characterize the subject-specific body dynamics as well as the intrasubject variabilities caused by excitation pattern (frequency up-sweep, down-sweep, and white noise, 1-10 Hz), excitation amplitude (1 and 2 m/s2 r.m.s.), seat compliance (rigid and soft), and stomach filling (empty and 500 mL water). Human subjects experiments (n = 3) yielded preliminary results for the frequency response of the head, sternum, and stomach. The method presented here provides the first detailed in vivo characterization of internal and external human body dynamics. Tissue dynamics characterized by the system can inform design of vehicle structures and adaptive control of seat and suspension systems, as well as validate finite element models for predicting passenger comfort in the early stages of vehicle design.

Comparison of the Shear Bond Strength of Metal Orthodontic Brackets Bonded to Long-term Water-aged and Fresh Porcelain and Composite Surfaces

Objective

The aim of the present study was to compare the shear bond strength (SBS) of metal orthodontic brackets bonded to long-term water-aged and fresh porcelain and composite surfaces.

Methods

One porcelain (Vitadur Alpha (VA)) and three composite (Filtek Ultimate (FU), Tetric EvoCeram (TEC), and Gradia Direct Anterior (GDA)) materials were evaluated in the present study. First, 10 discs from each material were prepared and subjected to the aging procedure for 5 years. Then, for comparison, another 10 discs from each material were prepared as fresh surfaces and stored in distilled water for 24 h. Metal brackets were bonded to the prepared disc surfaces, and after being stored in water for 24 h, they were subjected to shear bond test using a universal testing machine. Adhesive remnant index (ARI) scores were obtained by examining the disc surfaces under a stereomicroscope at 10× magnification. Kruskal-Wallis test was used to compare the aged and fresh groups.

Results

Although the difference between the SBS between the aged and fresh groups with VA, FU, and TEC was not significant, the SBS was significantly higher in the fresh group with GDA. With regard to ARI scores, there was no significant difference between the aged and fresh groups with FU and GDA, whereas the ARI scores of the aged groups with VA and TEC were higher.

Conclusion

It was concluded that the aged restoration materials have a distinctive influence on the SBS of metal orthodontic brackets.