A survey done recently showed that almost 30 percent of the accidents occurred during oral implant surgery were concerned with the mandibular canal in the trabecular bone region and most of them were related to the drilling process. One of the reasons known is due to the clinicians' lack of knowledge and experience. In order to overcome the problem, through the educational approach, we proposed and developed a new system mainly for dental colleges' students, by focusing on drilling the mandibular trabecular bone. The system comes in the form of an oral implant surgery training simulator that enables student to sense the reaction force during drilling. The developed system was then evaluated by expert clinicians and dental college's students. A total of 8 clinicians and 24 students tested all three samples of drilling force database. The clinicians were asked to describe the drilling force based on a stiffness scale while the students are required to drill two samples first before drilling the third sample. They were asked to sketch the third samples based on the comparison of previous samples. Based on the evaluation done, it was found that the quantification of force sensed during drilling could be derived from the combination of drilling force and speed obtained through the relative value of comparison with the previous or accumulated experience of drilling. The results of this study also indicate that the oral implant surgery training simulator could help students learn the difference of drilling force sense dependent on the bone quality through repeated usage and practices.
Atherosclerosis is a major cause of mortality and morbidity worldwide. In advanced atheromatous plaques, stiffening is often accompanied by calcification. Although the fibrous cap is more deformable than calcified regions, it is unknown to which extent it deforms with a presence of calcified region. In the present study, we excised human aortas with calcified/noncalcified plaques at autopsy and investigated the correlation between the presence of calcification and the deformation of the luminal surface. Rectangular specimens were stretched uniaxially in the circumferential direction. A digital image correlation (DIC) technique was applied to scattered spots on the specimen surface with an applied strain of 0.04 - 0.05 to obtain the distributions of normal strain in the stretching direction. The distance between the calcified region and the lumen was measured at the location of minimum strain on the luminal surface from cross-sections of computed tomography (CT) images of specimens and photographic images of formalin-fixed specimens. The calcified region was also identified upon histological examination. Our results showed that two calcified plaques had a minimum strain of zero on the luminal surface with calcified regions 10 - 20 μm off the lumen in the fibrous cap and one had a minimum strain of 0.006 with calcified regions 496 μm off the lumen in the lipid core, while two noncalcified plaques had minimum strains of 0.004 and 0.008. These results indicate that the local deformation of the fibrous cap is restricted completely in cases where it is calcified. The average deformation is about one tenth of that observed on the surrounding vascular tissue surface in the cases where calcification is not present, or is present in a deep layer of the fibrous cap or in the lipid core. These findings may facilitate better understanding of calcified plaques, aiding image-based diagnosis.
Prediction of rupture status in cerebral aneurysms remains challenging for clinicians, and the important rupture indicator (wall shear stress, WSS) is controversially discussed. Recent studies report that flow instabilities appear to play an influential role in the evolution and rupture of aneurysms and it is strongly correlated with both geometries and inlet flow rate waveforms. However, how frequency harmonics in inlet flow rate waveforms influence the flow instabilities and hence WSS fluctuations in cerebral aneurysms are still unclear. In this study, we used a computational fluid dynamic (CFD) model of anatomically realistic cerebral aneurysms combining with Fourier series and power spectral density (PSD) analysis to investigate the association between inflow waveform's harmonic frequencies and flow fluctuations in terminal cerebral aneurysms. Our simulated results demonstrated that there exists a harmonic frequency dependency in inlet flow rate waveforms inherently associated with flow instabilities in cerebral aneurysms: low-frequency harmonics play a crucial role in causing significant WSS fluctuations. This is partly explained by that the low-frequency harmonics govern a primary local adverse pressure gradient at late systole during flow deceleration, which induces flow instabilities while giving it sufficient time to develop into flow instabilities whereas high-frequency harmonics do not but decay rapidly. This implies that flow fluctuations in cerebral aneurysms may be of some robustness, dependent mainly on the primary harmonic frequency initiated by heart contraction but against unpredictable high-frequency perturbations in the inflow waveforms.
Fall-related injuries are one of the most common injuries in daily life. Occasionally, particularly in children and the elderly, fall accidents can lead to fatal injuries. Therefore, it is necessary to clarify the mechanism of human falls and to develop a method to prevent such accidents. In previous studies, many researchers have estimated fall-related injuries, such as bone fractures, using the finite element method or a dummy. However, to adequately evaluate fall injuries, the pre-injury phase (such as avoidance or protective reactions) should be evaluated, because impact forces are related to such reactions and their ineffectiveness may be the main cause of falls in children. Therefore, in this study, infants’ protective reactions were focused on as a first step in analyzing the pre-injury phase. The natural fall behaviors of 16 infants measured in a lab imitating a living room environment were captured. Then, the joint angle data were analyzed to extract the special features of fall behavior and determine the time at which the protective reaction starts. The special features of fall behavior such as the parachute reflex were extracted using the principal component method. In 12 out of 16 cases, the start time of the protective reactions was extracted using the singular spectrum conversion method. Then, the durations of protective reactions and skill of protective reactions were defined using principal component analysis. Using these definitions, we propose an evaluation method for the effectiveness of protective reactions in different fall behaviors.
Improving the inflow characteristics of the right ventricular function and pulmonary circulatory hemodynamics was essential for more precise evaluation of newly designed heart valves. To examine a pulmonary hemodynamics, the authors have been developing a pulmonary mechanical mock circulatory system. In this study, the pneumatically driven right atrium model was newly developed for clarifying the effect of atrial contraction on the dynamic behavior of pulmonary prosthetic valves. We focused on the hemodynamic behavior of the outflow mechanical heart valve of the right ventricle that could be affected by the right atrial dynamic motion. A medical-grade bileaflet valve was employed and installed into the outflow portion of the right ventricle model and examined its changes in hemodynamic behavior caused by the active right atrial contraction. With the active atrial contraction, hemodynamic waveforms of either the right ventricle or atrium were obtained using the modified pulmonary mock circulatory system. The characteristics with atrial contraction were well simulated as the natural hemodynamics. The right ventricular output increased by around 5% and the peak regurgitant flow at the moment of valve closing significantly decreased by the presence of the atrial contraction. Our mechanical circulatory system could simulate the end-diastolic right ventricular inflow characteristics. We found that the atrial contraction under the low pressure condition such as pulmonary circulation promoted earlier valve closing and prolonged closing duration of prosthetic valve. The simulation of right atrial contraction was important in the quantitative examination of right heart prosthetic valves for congenital heart malformation.
To analyze the biomechanical behavior of human bone, micro-CT image-based static FEM analyses considering trabecular architecture have been carried out. In the field of dental biomechanics, not only the static analysis but also dynamic analysis against impact load is required. In this paper, a desktop micro-CT was used for the right half of a human mandible with 0.103 mm resolution after dissecting. The lost information by a saw was recovered by the homogenization model. The impact load was applied to the implant in the molar part and the load transfer from the implant to the cortical bone and trabecular bone was considered. The stress wave pathways from the implant to the condyle were analyzed by comparison with virtual FEM models with eliminated materials on pathways. It was revealed that the stress wave transferred from the implant neck and end part to peri-implant trabecular bone played a significant mechanical role. It was also found that the apparent wave speed in the trabecular bone region was as fast as that in the cortical bone.
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