The Swarm rat chondrosarcoma is a well established model system for the biochemical studies of cartilage proteoglycans. In this study, we observed the ultrastructure of mitotic chondrocytes in this tumor to confirm whether it is also useful as a morphological model system to examine the mitosis of chondrocytes. As a result, the mitotic chondrocytes in this tumor contained fairly prominent cell organelles, and the endoplasmic reticulum was mainly vacuolized and the Golgi stacks were replaced by the cluster of small vesicles during the later stage of the mitotic cycle. Although the cytoplasmic division began at the telophase, the cytoplasmic cleavege furrow was so narrow that dividing chondrocytes looked as if they were partitioned by a slit. These findings are almost consistent with the changes that occurred in the mitotic chondrocytes of the tibial growth plate, although the degree of disorganization in the Golgi apparatus is slightly different. Therefore, this tumor is useful as a convenient morphological model system to examine the mitosis of chondrocytes because of the facility for taking specimens.

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In selecting the teeth for fabrication of complete or partial dentures, each patient s anatomic and physiologic requirements and the properties of the artificial teeth themselves should be taken into consideration. The purpose of this study was to evaluate the mechanical properties of the artificial teeth by the static compression test and the impact test. Specimens were the lower first molar porcelain and resin teeth (Livdent FB-20 teeth by G.C. Co., Tokyo, Japan). All were of the same shape. In the static compression test, the fracture load and deformation of the artificial teeth were measured with an Instron-type universal testing machine at a cross-head speed of 1.0 mm/min. Elastic modulus, ultimate strength and absorbed energy were calculated. In the impact test, the acceleration of a falling impactor was measured with a drop impact apparatus. The load applied to the specimen was equivalent to 300N. Absorbed energy and deformation were calculated. The resin teeth showed a lower elastic modulus, higher fracture toughness and shock-absorbing ability than the porcelain teeth. Resin teeth should be selected when the first requisite is high shock absorbing ability, and porcelain teeth should be selected when the first requisite is high masticating efficiency.

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The mandibular first permanent molar has been reported to be the first permanent tooth to erupt. However, according to the recent reports, a considerable increase in the number of children has been observed with the eruption of the mandibular first permanent molar after the eruption of the mandibular central incisor. The purpose of this study is to investigate whether there is any morphological difference in the mandible including the mandibular corpus and the ramus between the subjects with the mandibular first permanent molar erupting prior to the mandibular central incisor (Group A) and the subjects with the mandibular central incisor erupting prior to the mandibular first permanent molar (Group B). Lateral, posteroanterior, 45-degree oblique cephalometric radiographs and dental plaster models were used as the materials. Based on the data statistically analyzed, the results are summarized as follows: 1. No significant differences were found in the conventional angular lateral cephalometric measurements between the two groups. 2. No significant difference was found in the mandibular length between the two groups. 3. Significant differences were found in the mandibular corpus and the ramus between the two groups. In other words, the children in Group A have a narrower ramus, longer corpus and a larger eruption space for the mandibular first permanent molar than the children in Group B. These results indicate that even though there was no significant difference in the anteroposterior dimension of the mandible between the two groups, the internal proportion of the mandible represented as the ratio between the corpus and ramus was significantly different. This may suggest that the different proportional constituents of the mandible have a close relationship with the eruption timing of the mandibular first permanent molar.

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In a series of studies to investigate the structural features of the biological crystals, using electron microscope, we examined the ultrastructure of the human dentin crystals at near atomic resolution through the cross and longitudinal sections of the crystals The materials used for this study were the deep layer of the non-carious coronal dentin from freshly extracted human erupted permanent molars. The small cubes of the dentin were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut wth a diamond knife without decalcification. The sections were examined with the HITACH H-700 type of transmission electron microscope operated at 200kV. Each crystal was observed at the initial magnification of 300,000 times and at the final magnification of 10,000,000 times and over. Using this approach, the authors have been able to show the configuration of the hydroxyapatite structure in the cross and longitudinal sections of the dentin crystals deposited within and between the collagen fibrils (intrafibrillar and interfibrillar crystal) in the intertubular dentin and observe the basic hexagonal pattern of the unit cell viewed down the c axis. The authors sincerely believe that the electron micrograph shown in this report is the first atomic image to be obtained from a hydroxyapatite crystal from the human dentin, using the sections.

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The purpose of this study was to determine the immunodominant antigens of P. gingivalis 381 and to examine their composition and molecular weight. Fourteen periodontal patients, with high antibody titers to P. gingivalis 381 sonicated extract, were selected. Whole cell fraction, sonicated extract and outer membrane protein of P. gingivalis 381 were used as antigens in the untreated form as well as in the heated form and treated with papain. Total volume of sugar, protein and lipopolysaccharide (LPS) was estimated in each one of the three antigens. Antibody binding capacity to the three antigens was evaluated, before and after heat and papain treatment, by an enzyme-linked immunosorbent assay (ELISA). In addition, the immunoblotting analysis was performed. The quantitative assays showed that the whole cell fraction contained about ten times more LPS than the other two preparations while the outer membrane protein contained twice the amount of carbohydrates than the other two preparations. The 14 sera were classified into three groups according to the rate of reduction of antibody binding under heat and papain treatment. Concerning heat treatment, most of the sera showed a high reduction of antibody binding when reacting with the sonicated extract. However, antibody binding to the outer membrane protein antigen was hardly decreased by heat treatment in three sera. Also, these three sera showed almost the same response to the whole cell fraction antigen under heat treatment. Under papain treatment, almost all sera showed a moderate reduction of antibody binding when they reacted with the sonicated extract and whole cell fraction while they showed a low reduction of antibody binding when they reacted with the outer membrane protein. From the present study it could be concluded that a main proteinaceous antigen of P. gingivalis was recognized by the majority of the patients suggesting that the proteinaceous portion is an important part of the antigen, while some patients seemed to recognize the LPS or carbohydrate as the antigenic determinant.

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Since 1980 we carried out a longitudinal dental survey in Ile-Ife, as a joint study with the dental school of Ife University, Nigeria, being supported by A Grant under The Monbusho International Scientific Research Program for ten years. One thousand one hundred seventy-one children and adults were examined in the 1991 survey. The data were compared with the data in the previous survey and Japanese survey. Results were as follows: 1) Caries prevalence rate and the average number of DMFT were still very low, especially showing that both the caries prevalence and the average number of DMFT decreased in the rural areas because the attrition proceeded faster than the caries, 2) Nigerian deciduous and permanent dentition were larger than in the Japanese in all items measured , 3) the condylar head was transform ed from the round shape to the ultra-flat shape with age, 4) there was a fewer incidence of severe periodontal diseases despite of the marked deposition of calculus, 5) with respect to Nigerian foods, there was no difference between the rainy and dry seasons in both the urban and rural communities, 6) the weaning period of the baby is decided by their mother, taking care of the health of the baby, almost all babies at one year to two years and a few at three years and 7) the menu for the breakfast, lunch and supper of the baby was made considering the nutritional aspect of the baby.

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