Comparison of biomechanical properties of the incisor periodontal ligament among different species

BACKGROUND: The aim of this study was to obtain a more precise understanding of the mechanical properties of the periodontal ligament in continuously erupting incisors by comparing the shear stress-strain relations among teeth from four closely related species. METHODS: Four species of experimental animals (mice, hamsters, rats, and rabbits) were used. Transverse sections of the left mandibular incisors were cut from the incisal, middle, and basal regions of each incisor. The tooth was pushed out of the alveolar bone in an extrusive direction at 5 mm/min using a materials testing machine. The maximum shear stress, maximum shear strain, tangent modulus, and failure strain energy density were estimated from the resulting stress-strain curve. Polarized light microscopic observations of collagen fibers were also made. RESULTS: All the biomechanical measures tended to decrease from the incisal toward the basal regions in all species. There were large species differences, especially in the incisal region, with the greatest maximum shear stress and failure strain energy density in hamsters. The greatest tangent modulus and the smallest maximum shear strain were observed in mice. The birefringent fiber architectures of the periodontal ligaments in the four species appeared to be similarly organized; the incisal periodontal ligament appeared to have more organized and thicker collagen fibres than did the middle and basal ligaments in the four species. CONCLUSIONS: These results suggest that the regional differences in the biomechanical properties of the periodontal ligament depend upon the developmental stages of the periodontal collagen fibers that may be related to the general arrangement, diameters, and densities of the collagen fiber bundles and the fiber insertions into the alveolar bone and cementum. The species differences in the biomechanical properties may be due to differences in the width of the periodontal ligament and the waviness as well as the strength and stiffness of the periodontal collagen fibers.     

Preparation and morphology of as-prepared and highly stretch-aligned polyacetylene

The macroscopic morphology of as-prepared polyacetylene depends on the concentration of the catalyst system. At high catalyst concentration, polymerization occurs on the free surface of the catalyst solution to form a polyacetylene film which retards further polymerization because of the limited diffusion of acetylene monomer through the film. At lower concentrations, however, successive diffusion and polymerization is possible yielding a gelatinous mass. A continuous mass does not form at an extremely low concentration; the product is flock or powder. Despite these differences in macroscopic morphology, electron micrographs show that the fibrillar structure is a common feature of all forms of polyacetylene. However, the average fibril diameter of 200 Å may depend on the polymerization conditions. Orientation of the fibrils by combined mechanical and thermal treatment is possible to produce highly stretch-aligned films which show anisotropic properties.     

Cell cycle analysis of Chinese hamster ovary cells stimulated by phosphatidic acid in serum-free culture

When recombinant Chinese hamster ovary cells were treated with pertussis toxin or genistein, not only lysophosphatidic acid (LPA) but also phosphatidic acid (PA) failed to stimulate progression through the cell cycle in serum-free culture, suggesting that PA and LPA induce cell growth through the same signal transduction pathway. Cell cycle analysis also indicates that cell growth promoted by PA results in enhanced protein production.     

Rate of emulsion polymerization of styrene

In emulsion polymerization, the Smith and Ewart theory gives about two or three times the number of polymer particles obtained by experiment. In this paper, a reaction model is proposed which, from the standpoint of reactor design, can give an adequate explanation of the whole course of an emulsion polymerization of monomer highly insoluble in water. Among other things, the generating process of polymer particles is examined in detail. It is demonstrated experimentally that a new parameter proposed here, which represents the degree of difficulty of monomer initiation in micelles, is indispensable in explaining that process. Also confirmed is that monomer initiation takes place more easily in polymer particles than in micelles. According to the new model, the progress of polymerization, i.e., monomer conversion, the number of the polymer particles, and properties of polymer thus produced can be estimated with satisfactory accuracy. Furthermore, approximate equations are derived for easier estimation.     

Pulsed laser irradiation impact on two marine diatoms Skeletonema costatum and Chaetoceros gracilis

The ability of pulsed laser irradiations to cause damage on the biofouling organisms is recently being investigated. If this technique is employed in industries such as power generation wherein a large quantity of water is being used for the cooling purpose, many organisms other than the targeted would get affected. In this study, we have investigated the damage caused by the pulsed laser irradiations from an Nd:YAG laser (fluence 0.1J/cm(2)) for varying durations such as 2, 5, 10, 30, 60 and 300 s on two marine diatom species namely Skeletonema costatum and Chaetoceros gracilis. Upon exposure to low power laser irradiations, these diatom species showed mortalities between 52.6+/-9.3% to 97.7+/-3.1% in the case of S. costatum and 57.8+/-2.5% to 98.9+/-0.6% in the case of C. gracilis for 2 and 300 s of irradiations, respectively. The mortality increased with the increase in the duration of laser irradiation. The estimation of the chlorophyll a concentration in the irradiated samples showed a considerable reduction varying between 9.8% and 57% in C. gracilis and 3% and 70.3% in S. costatum for 2 and 300 s of irradiations, respectively. The laser-survived cells grew as the non-irradiated (control) samples. C. gracilis frustules were broken by the laser whilst, the cell materials were drained out of the frustules in the case of S. costatum. The study therefore showed that the low power pulsed laser irradiations could cause significant damage on the two species of planktonic diatoms.