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歯科用貴金属合金の擬似口腔内環境における腐食挙動
Get PDFapplication/pdfThe corrosion resistance of twelve commercially available dental precious metal alloys, pure titanium and Ti6A14V alloy was investigated by measuring anodic polarization and open-circuit potential in de-aerated 1 mass%-lactic acid solution. The open-circuit potentials (E_) ranged from -0.8 to 0.3V vs. SCE and decreased as follows; porcelain-fused-to-metal dental alloys>gold alloys>gold-silver-palladium alloy>silver alloy>pure titanium>Ti6A14V alloy. Open-circuit potentials (E_) and zero-current potentials (E_z) of the porcelain-fused-to-metal dental alloys and the silver alloy were approximately equal. However, the zero-current potentials (E_z) of the gold alloys, the gold-silver-palladium alloy, the pure titanium and the Ti6A14V alloy were lower than each open-circuit potential (E_). The critical current densities for passivation (I_) were of the order of 10^ to 10^1 A・m^. In the silver alloy, the critical current density sharply increased. The values of common logarithm (Log_Q (E_z+E_)) of the integrated corrosion values (Q(E_z+E_)), corresponding to the integrated current density between the zero-current potential (E_z) and the potential of E_z+0.3V (E_z+E_) vs. SCE, was calculated from the anodic polarization curve. Regression analysis was carried out for their values and nobility (Au+Pt+Pd) atomic% indicated that the values of the common logarithm (Log_Q(E_z+E_)) varied linearly with nobility (Au+Pt+Pd) atomic% for the twelve commercial dental precious metal alloys. Furthermore, the values of the common logarithm (Log_Q(E_z+E_)) of the integrated corrosion values (Q(E_z+E_)) of the gold alloys and the gold-silver-palladium alloy were monotonically proportional to Ag/(Au+Ag+Cu) atomic ratio. Based on the findings of this study, it was suggested that dental precious metal alloys with high nobility and gold alloy with a lower Ag/(Au+Ag+Cu) atomic ratio have high corrosion resistance in the pseudo-oral environment.journal articl
有限要素法の原理と歯科における応用
Get PDFapplication/pdfThe finite-element method (FEM) was developed in the 1950s, and is comparatively new. The application range of FEM is very wide; for example, FEM is used in the field of the design of the buildings, cars, aircraft, acoustic equipment, dams and the tunnels, simulation of the global environment, the comet crashes and so on. Therefore, FEM is an indispensable method at present. As for the medical field, FEM is applied to changes of the endovascular bloodstream, inner stress on the jawbone distributed by articulation, periodontal features when receiving an impact and so on. Current personal computers have 10000 times the throughputs of mainframe computers in the 1970s, so impressive analysis is possible without problems. Also, Japanese researchers have the initiative in the world in this field of dentistry. FEM can be analyze flow and heat etc. in addition to structure; therefore, novel ideas from young researchers are expected.journal articl
Posterior discrepancyについて : パノラマエックス線写真による計測法の評価
Get PDFapplication/pdfArch length discrepancy is one of the most important factors in orthodontic diagnosis. This is considered to involve two parts of anterior and posterior discrepancy. Anterior discrepancy is defined as a difference between available arch length which is obtained by measuring the arch perimeter mesial to the first molar and total tooth size of the second premolar to the other side. Recently, posterior discrepancy has been considered a relevant measurement in orthodontic practice. Posterior discrepancy can be defined as a difference between available arch length posterior to the first molar and total tooth size of the first, second, and/or third molars. However, analysis of posterior discrepancy has not been established. This study was to assess the analysis of posterior discrepancy on panoramic image, in comparison with the actual length of a human dry skull. Fifty human dry skulls were used in this study. Two dental panoramic image photographs of the dry skulls with and without metal wire were taken for each skull. Measurement of the actual length of all dry skulls and measurements of the panoramic image of the skulls were measured on both sides of the upper and lower jaws. Five different methods of measurement were tested on panoramic image on both sides. The best measurement of upper posterior discrepancy was obtained by calculating the distance between perpendicular to occlusal plane from half the arc of Ptm and most posterior teeth to the distal line of the second molar. The best measurement of lower posterior discrepancy was obtained by calculating the distance between the intersection points of the anterior ramus line and the horizontal line through the widest points of the second molar and the distal line of the second molar.journal articl
Capital Investment and Corporate Finance of the State Industry in the NEP era
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マウスガードの歯および歯周組織への効果
Get PDFapplication/pdfVarious types of protective equipment for sports have been developed, such as mouth-guards used in the maxillo-oral region. Mouthguards are considered to exhibit excellent maxillo-oral injury-preventive effects, and their use is recommended in many sporting fields, particularly in contact sports. However, in previous studies on the injury-preventive effects of mouthguards, their impact absorbability was evaluated only by applying impact to mouthguard materials, and by inserting mouthguards into cranial bone models or extracted bovine teeth, without assuming actual impact to the body, or considering the presence of periodontal tissue consisting of the periodontal membrane, alveolar bone, and gingiva. Therefore, the effects of mouthguards on periodontal tissue have not been clarified. In this study, using a pendulum-type impact test machine, impact was applied to bovine mandibular bone bodies whose periodontal tissue had been preserved under conditions highly similar to physiological condition the actual effects of mouthguards, and influence of differences in the thickness and composition of mouthguard materials on the teeth and periodontal tissue were evaluated. The following results were obtained: 1. Impact force applied to the teeth and values for strain occurring in the teeth were significantly lower in the presence than in the absence of a mouthguard. 2. Similarly, the values for strain occurring in alveolar bone periodontal tissue area significantly decreased after wearing mouthguards, in contrast to the absence of mouthguards. 3. Impact force applied to the teeth and values for strain occurring in the teeth were significantly lower with a 4-mm-thick mouthguard than with a 1-mm-thick mouthguard. 4. Similarly, values for strain occurring in the alveolar bone periodontal tissue area (lingual side) were significantly lower with a 4-mm-thick mouthguard than with a 1-mm-thick mouthguard. 5. Differences in mouthguard materials did not cause any significant difference in the impact force applied to the teeth or the strain occurring in the teeth. 6. Differences in mouthguard materials did not cause any significant differences in strain occurring in the alveolar bone periodontal tissue area. These findings suggest that mouthguards decreased the values for strain and degrees of impact acceleration caused by impact force applied to the teeth and alveolar bone area, protecting the teeth and periodontal tissue. Furthermore, our study confirmed that the impact absorption effects of mouthguards on the teeth and periodontal tissue increased with increases in their thickness. It was also suggested that differences in mouthguard materials employed in this study did not show any significant difference in the impact absorption effects on the teeth and periodontal tissue.journal articl
Regenerative Medicine of Bone and Teeth: with special references to biological principles, problems and their indicators\n
Get PDFapplication/pdfSo much anticipation from the side of need patients has been caused by recent advances in tissue engineering technology. However, it seems that effective results can be hardly achieved unless we establish the proper principles for this technology. In this review paper, therefore, we discuss these problems and indicators from the viewpoint of the biological principles of hard tissue regeneration, which are as follows: 1) principles of hard tissue reconstruction, 2) bio-functional nano-composites for regeneration of hard tissue, 3) industrialization of growth factors for hard tissue reconstruction, 4) history and problems of medical ceramic materials, and 5) dentin matrices as a new autograft material for osseous regeneration.journal articl
左鎖骨下動脈を最終枝とする右側大動脈弓の1例
Get PDFapplication/pdfIn this study, we found right aortic arch with left subclavian artery as its last branch in the cadaver of an 84-year-old Japanese male during anatomy practice at Matsumoto Dental University in 2006. The ascending aorta curved right and backward to form the aortic arch. Four branches extended from the aortic arch in the following order from left to right: the left common carotid, the right common carotid, the right subclavian and the left subclavian arteries. The left subclavian artery ran left and upward behind the esophagus. The ligamentum arterio-sum connected the left pulmonary artery with the left subclavian artery. The present case was considered the Nal-type according to the classification by Shibata et al. (1998) and was the 26th case of N-type aortic arch reported in Japan.journal articl