Transplantation of mesenchymal stem cells promotes maturity of the distracted callus. The new experimental model, which allowed to test the mandible as a system by simulating in vivo loading conditions, revealed differences in the mechanical behavior of the halves of mandible.
In this experimental study, the goal was to test the sufficiency of actual fixation plates in zygomatic complex fractures and the efficiency of a modified plate at the zygomaticofrontal suture in a suitable model, which was designed for biomechanical study. To address this issue, a zygomatic fracture model produced by using a cadaveric cranium was simulated and the fractures were fixed by the actual and modified fixation materials. The force simulating masseter muscle pull was applied with the Lloyd material testing apparatus, and the rotation of the zygoma was determined using displacement transducers. In this study, there were three different experimental groups. Although miniplates at the zygomaticomaxillary buttress and microplates at the infraorbital rim were used in all three groups, three different plates (miniplate, microplate, and modified plate) were used at the frontozygomatic suture in these groups. Rotational displacement of the zygoma with the effects of simulated masseter muscle force was determined. According to the results obtained, microplates are not effective in stabilizing the frontozygomatic suture when the masseter muscle forces are within physiological range. Although miniplates stabilize zygomatic complex fractures, it was shown that modified microplates, which have no ondulation along the plate border, have a higher resistance to rotation than that of the conventional plates. The rotation angle at the instant of fracture with microplates was 4.59 degrees, and that with miniplates was 1.26 degrees. The maximum rotation angle with modified microplates was 0.32 degrees. Modified microplates designed for the fixation of fractures in the zygomatico-orbital region have been shown to be suitable in a well-designed experimental model and might be appropriate for clinical use.
Abstract:To examine the evolution of inter-segmental coordination over time, a previously developed multi-variate model of postural coordination during quiet stance (Kuo et al. 1998) has been extended. In the original model, postural coordination was treated as an eigenvalue-eigenvector problem between two segmental degrees of freedom represented by angular displacements of the trunk and lower limb. Strategies of postural coordination were then identified using the sign of the covariance between the two segments' angular displacements. In contrast to the original model, the current model first subdivided the entire trial into smaller time segments, comprising four cycles of perturbation, i.e., a 16 sec window. This window marched along the data advancing in 8.3 ms steps, each time performing the computation from the original model on the terms of the covariance matrix. The resulting time-segment-dependent postural strategies estimated the changes in posture control that took place over the course of the experiment. In addition to the statistical modeling, the auto-power spectrums and cross-spectral density function estimates for the entire trial, as well as for the individual time-segments, were analyzed. In these experiments subjects experienced a 0.25 Hz sinusoidal perturbation of a platform while exposed to a virtual reality environment. The data we collected showed that the statistical and spectral characteristics across the entire trial may differ from individual time segments of the same trial indicating time varying postural behavior. Comparison of these results from young and elderly subjects revealed that the time dependency observed in postural behavior was sensitive to aging. The young population managed to be consistent in their postural behavior throughout the entire trial and responded to the perturbation frequency with an out-of-phase response between the postural segments. Elderly subjects, however, demonstrated inconsistent postural behaviors as they switched back and forth between different postural coordination patterns within a trial.
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