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Displacement of actin filament and its binding proteins in mouse myoblasts under locally applied deformation was analyzed by manual method or digital image correlation method. Cyotoskeletal components labeled by immunofluorescent technique or green fluorescent protein-fused protein were deformed via the movement of a glass needle which was poked into a cell. First, we confirmed the digital image correlation method is able to use to analyze displacement map by comparison of the manual method. Next, we examined whether the applied deformation isotropically propagates into cell body. At focal adhesions, fluorescent signals from the deformed area unchanged under the application. Mainly, focal adhesions around the poked area were moved to the direction of the movement of the needle. In addition, some adhesions away from the poked area were moved. Similar results were observed in phalloidin-stained cells. Finally, we applied the local deformation to live cells. However, displacement at the locally deformed area was not observed due to the disappearance of fluorescent signals. These results indicate that applied deformation propagated heterogeneously into a cell, and may imply that biochemical signals disrupt actin fibers under local deformation.

A porcine mandible was separated to prepare thin periodontium specimens, consisting of a molar, periodontal ligament (PDL), and alveolar bone. Occlusion was simulated by applying a forced compressive displacement, using a table-top material tester. We photographed images of the displacing periodontium specimen and simultaneously obtained the load-displacement curve during the test. The displacement and deformation distributions were examined using digital image correlation analysis. Then, we correlated the distribution with the load-displacement curve, which was characterized by biphasic behavior, as noted in many previous studies. We found that the displacement and deformation distributions of actual periodontium correlated with the load-displacement curve during dental occlusion. Regarding the biphasic characteristics of the load-displacement curve, we showed experimentally that the first phase indicated deformation of the PDL and the second indicated deformation of the alveolar bone and tooth.

The polymerization shrinkage of dental restorative resin composites in cavities was studied using a digital image correlation method. The cylindrical and semi-cylindrical cavities in bovine teeth were used to examine the shrinkage behavior on the top free surface and the simulated cross section, respectively. The cavities filled with the resin after spreading a bonding agent were irradiated using a visible-light curing unit and photographed with a CCD camera as a function of time. The two images photographed were correlated to study the deformation during the polymerization process. Experiments were also performed on the cavities without the bonding agent, and its effect on the bonding strength at the interface between the resin and tooth structure was examined.

In this study, we clarified dental occlusion functions by visualizing the displacement and deformation patterns of the periodontium under dental occlusion. A digital image correlation method served as a visualization and deformation analysis method using fresh porcine periodontium specimens. Also using dried periodontium specimens, we conducted the occlusion test to characterize the differences in displacement and deformation patterns between fresh and dried specimens. Results indicated that the periodontal ligaments deform first, followed by alveolar bones. Marked differences in displacement and deformation patterns were observed between the fresh and dried periodontium specimens.