A porcine mandible was separated to prepare thin wet periodontium specimen consisting of a retromolar, periodontal ligament, and alveolar bone. Occlusion test was simulated by applying a forced compressive displacement using a tabletop material tester. We photographed the images of the displacing periodontium specimen and obtained the load-displacement curve during the test. The displacement and deformation distributions were visualized by a digital image correlation analysis. Then, we correlated the distributions with the load-displacement curve, which characterized by biphasic behavior in many previous studies. Additionally, to clarify the potential of dried periodontium specimens as the occlusion specimens, similar experiments using well dried periodontium specimens were conducted to compare the distribution and the load-displacement curve to the wet ones. The results were as follows. (1) We succeeded that the displacement and deformation distributions were correlated with the load-displacement curve for the first time. (2) In the biphasic behavior of the load-displacement curve, we experimentally revealed that the first phase indicates the deformation of the periodontal ligament, and the second one indicates the deformations of the alveolar bone and retromolar. (3) A significant difference was observed in the displacement and deformation distributions and the load-displacement curves between the wet and dried periodontia specimens.

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A digital image correlation method was applied to study the polymerization shrinkage of a light cure resin composite in cavities of bovine teeth. A cylindrical cavity prepared using a bonding agent was employed to measure the shrinkage behavior on the top free surface of the cavity. A semi-cylindrical cavity was also used to simulate the cross section of the cylindrical cavity. The resin filled in the cavity was irradiated using a visible-light curing unit and photographed with a CCD camera as a function of time. The cavities prepared without the bonding agent were employed to study the bonding strength at the interface between the resin and tooth substrate, and the following results were obtained. The shrinkage behavior was largely different in the cavities prepared with and without the bonding agent. With the bonding agent, the displacement distribution was continuous at the interface, and its absolute value exhibited the maximum in the resin close to the interface and the minimum near the center of the cavity. Without the bonding agent, there existed the interface which exhibited the discontinuous distribution, and the discontinuity tended to initiate and grow locally at the interface.

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Dentin is a natural composite material consisting of three phases: mineral, organic and water. These three phases are not independent each other, but rather work in harmony to determine the viscoelastic property of dentin. Although the viscoelastic properties of root dentin at a macroscopic level have been studied, those of the crown to root dentin at a microscopic level have not. Dynamic nanoindentation is a new promising method of measuring the dynamic viscoelastic properties of biological tissues with a smaller length and using smaller load scales than those allowed by other testing methods. The objective of the present study was to use the dynamic nanoindentation method to determine dynamic viscoelastic properties such as storage modulus and loss tangent of human crown to root dentin at the microscopic level in a tooth direction. The effects of dentin mineral density (DMD) measured by pQCT on viscoelastic properties at a macroscopic level were also studied. The DMD at the crown dentin was higher than that at the root dentin. The storage modulus of crown dentin was higher than that of root dentin, however the loss tangent of crown dentin was lower than that of root dentin. It was found that a positive correlation existed between the storage modulus and DMD (r = 0.72). The loss tangent was negatively correlated with DMD (r = - 0.23).

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The fixation between a beads-type porous-surfaced dental implant and a surrounding bone is dependent on 3-dimensional anchoring effect which new bones develop into a porous structure. The speed of a bone ingrowth into the porous structure and the good fixation to bone is strongly related to biocompatibility of the implant. To impart a functional fixation by biointegration to the implant, in this study, a pulsed laser deposition (PLD) technique was used to form 300 nm thick hydroxyapatite (HA) film even on the depths of the porous structure. Through X-ray diffraction (XRD) and energy dispersive X-ray spectrometry (EDX) analysis, it was found that HA was crystallized and was deposited on the depths of interconnecting pores of complicated shape. The implants were placed into posterior regions of completely edentulous mandible of a canine. The bone ingrowth condition was scanned by CT scanner. In three weeks after operation, the bone ingrowth speed in the HA-deposited implant was increased as compared with the non-HA-deposited one. In five weeks after operation, no particular differences on the bone ingrowth between the HA-deposited and non-HA-deposited implants were found. HA thin film deposition on a porous-suerfaced implant was effective in the improvement of functional bone fixation.

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The purpose of this study was to photoelastically compare the load transfer characteristics of a distal extension RPD of periodontally compromised abutments with and without implant assisted support in the posterior of a mandible. Two composite photoelastic models of a mandible that included reduced periodontal support of the connected canines and first premolars bilaterally were constructed with different simulants for teeth, bone and periodontal ligament. In one model threaded implants, 3.75mm diameter 7mm length, (Nobel Biocare) were embedded 20mm distal to the first premolars on the posterior edentulous ridges. I-bar partial dentures with mesial rests and distal guide planes were fabricated and physiologically adjusted to the models. The implant support conditions tested were support of 4mm healing abutments. Simulated vertical and lateral occlusal loads were applied at the first molar position and the stresses developed in the abutment teeth and surrounding bone were monitored photoelastically. Both vertical loads and lateral loads, applied to the denture base supported by implants with healing abutments generated high stress concentrations around the apices of ipsilateral implant and the abutment teeth. Posterior implants with healing abutment in the posterior of a mandible tended to assist support of periodontally compromised abutment teeth. of a distal extension RPD.

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It is recognized that the occlusal force is transmitted through the tooth and the periodontal membrane to the alveolar bone. As the periodontal supporting tissue is destroyed by periodontal disease, the occlusal force may tend to concentrate to the remaining tissue. In this study, the mechanical stress to the root apex was experimented by the various conditions of the alveolar bone defects. The quasi-three dimensional photoelastic models of premolar and molar mandibular teeth were used to estimate the stress. These models were loaded up to 98.0N, the color fringe changes were observed. This study suggests that the mechanical stress from the occlusal surface was spread to the wide area of alveolar bone and its surrounding tissue as the load was increased. The stress was concentrated to the root apex regardless of the shape of infrabony defects, and compression and tension of tooth were observed on the root surface. The color fringe pattern was changed by infrabony wall defect.

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In generally, it is known that structures of living things are optimized. The wings of a dragonfly are very thin and light. Although it is having the structure of bearing the load produced in the case of an advanced flight such as “Flapping flight”, “Glide”, and “Hovering”. The wings of a dragonfly are made by veins and membranes. In addition, the wings of a dragonfly have some characteristic structures, such as “Nodus”. Thus, the wings of a dragonfly have many complicated structures. The costal vein configuration of the wings of a dragonfly is different from them of other insects. So, we paid attention to the costal vein configuration of the wings of a dragonfly. Therefore, in this study, we researched about the effect of the costal vein. As a result, it was showed that the configuration of costal vein made the deformation of bending and torsion small. In addition, it was showed that the configuration of costal vein closely related to nodus. In this study, several 3-D models of the dragonfly's wing were created and analyzed by the 3-D finite element method (FEM).

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Magnetic compound fluid is regarded as a mixture of magnetic fluid with particles of nanometer size and magneto-rheological fluid with particles of micron size. The magnetic rubber which is produced by mixing the magnetic compound fluid and a silicone rubber has strong saturation magnetization and small coercive force compared with magnet sheet. In this research, responses of the coupled system of the magnetic fluid layer and the magnetic elastic membrane to applied traveling magnetic field that is generated by 12 coils are investigated experimentally. It is shown that the wave on the magnetic elastic membrane is generated and propagated by applying traveling magnetic field. The amplitude of the wave is affected by frequency of applied magnetic field and depth of the magnetic fluid layer.

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