Shape Optimization of Bone-Bonding Subperiosteal Devices with Finite Element Analysis

Subperiosteal bone-bonding devices have been proposed for less invasive treatments in orthodontics. The device is osseointegrated onto a bone surface without fixation screws and is expected to rapidly attain a bone-bonding strength that successfully meets clinical performance. Hence, the device’s optimum shape for rapid and strong bone bonding was examined in this study by finite element analyses. First, a stress analysis was performed for a circular rod device with an orthodontic force parallel to the bone surface, and the estimate of the bone-bonding strength based on the bone fracture criterion was verified with the results of an animal experiment. In total, four cross-sectional rod geometries were investigated: circular (Cr), elliptical (El), semicircular (Sc), and rectangular (Rc). By changing the height of the newly formed bone to mimic the progression of new bone formation, the estimation of the bone-bonding strength was repeated for each geometry. The rod with the Rc cross section exhibited the best performance, followed by those with the Sc, El, and Cr cross sections, from the aspects of the rapid acquisition of strength and the strength itself. Thus, the rectangular cross section is the best for rod-like subperiosteal devices for rapid bone bonding

MAGNETIC RESONANCE IMAGING AND PATHOLOGIC STUDIES ON LATERAL FLUID PERCUSSION INJURY AS A MODEL OF FOCAL BRAIN INJURY IN RATS

In this study, morphologic changes in brain lesions initiated by moderate lateral fluid percussion injury in rats were investigated chronologically using high resolution magnetic resonance imaging (MRI) and histopathologic methods. Rats were subjected to moderate fluid percussion injury (average 2.80±0.48 atmospheres) over the exposed dura overlying the right parietal cortex. MRI obtained in vivo were compared with corresponding pathologic findings at 1, 6, and 24 h and at 3, 6,14 and 80 days after injury. T2 weighted images showed scattered low signal intensity in the injured cortex within a few hours after injury, whereas histologic findings revealed intraparenchymal hemorrhages. T2-weighted images of the ipsilateral cerebral cortex and/or corpus callosum showed a high-signal-intensity area 4 h after injury. The high-signal-intensity area became largest in size between 6 and 24 h, then declined gradually, and almost disappeared 14 days after injury. Histologic examination revealed pyknosis, retraction of the cell body of neurons with vacuolated neuropil in the corresponding regions 6 and 24 h after injury, and cystic necrosis 14 days after injury. The location and extent of these pathologic changes were depicted accurately by MRI in vivo. In the hippocampus, pyknosis and retraction of the cell body of pyramidal neurons were observed on the injured side 24 h after injury, and the number of neurons in the CA1 and CA2『 CA3 regions decreased significantly on the same side by 14 days after injury. It is concluded that morphologic changes in the brain following experimental traumatic brain injury in rats are detectable in υivo by high-resolution MRI, and that MRI may be useful for the evaluation of treatment effects in experimental brain injury