The aim of this study was to examine the effect of a bending treatment on miniplates used for bone fixation in oral surgery : the occurrence and propagation of crack on the surface of the plates were studied. Five commercial titanium plates and one stainless steel plate were bent at angles of 60 and 20 degrees followed by SEM observation. Surface topographies of the plates affected crack occurrence significantly. Cracks were clearly observed at the edge of the parallel region of the plates bent 60 degrees. Cracks propagated from the defects produced by the manufacturer under fabrication process on the surface of one plate. Crack occurrence was not evident on the plates bent 20 degrees. Crack occurrence at the edge of the titanium plate was more severe than that of the stainless steel plate. Since the occurrence of microcracks during bending treatment might influence the fracture of the plate in vivo, we suggest careful bending treatment to avoid the occurrence of microcracks on the surface.

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There is a correlation between bone mineral density (BMD) and craniofacial morphology. Polymorphisms in the 3' end of the vitamin D receptor (VDR) gene have demonstrated a correlation with the bone mineral density (BMD) of several skeletal sites, but the relation of VDR polymorphisms to craniofacial morphology is not known. In this experiment, the correlation between VDR polymorphisms and 5 linear measurements (cranial base length, N-S; maxillar length, A'-PTM'; mandibular ramus length, CD-GO; mandibular corpus length, GO-POG'; and overall mandibular length, CD-GN) concerning craniofacial morphology was examined in a normal Japanese female population. Genomic DNA as a template was extracted from the blood of each subject, and the VDR polymorphism was determined by polymerase chain reaction-restriction length polymorphism (PCR-RFLP) with three restriction enzymes (BsmI, ApaI, TaqI). Five linear measurements from a lateral cephalogram and body height were also assessed for each subject. Although VDR is known to play important roles in regulating bone growth and BMD, which influence craniofacial morphology, no statistically significant correlation was observed between VDR polymorphisms and 5 linear craniofacial measurements or body height. The polymorphisms of the VDR gene do not play a significant role in determining craniofacial morphology. The strategy of this study would be useful for evaluating a genetic background in craniofacial morphology.

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To study the provision of a suitable microenvironment for reparative dentine formation, wound healing in rat molar pulps was examined by light and electron microscopy following pulp amputation and direct capping with calcium hydroxide paste, folmcresol, or high molecular-weight hyaluronic acid. The effects of these pulp capping agents were compared. In hyaluronic acid-treated pulps, at 2 days after amputation, wound surfaces were covered with blood and fibrin clots and inflammatory cells such as neutrophils and macrophages. At 1 week after amputation, odontoblast-like cells produced globular calcified nodules along the existing dentine walls. At 2 weeks, a layer of reparative dentine had been formed by odontoblast-like cells over the dentine walls. Between 30 and 60 days, the formation of reparative dentine had extended throughout the pulp chamber. The healing observed after direct capping with hyaluronic acid was, except for the formation of dentine bridges, similar to those seen after calcium hydroxide or formcresol capping. These results suggest that high molecular-weight hyaluronic acid can provide an environment suitable for reparative dentine formation through mesenchymal cell differentiation during healing of the amputated dental pulp.

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To evaluate changes in the viscoelastic properties of the periodontal ligament accompanying tooth movement from a histological perspective, the upper third incisors of adult mongrel dogs were moved mesially with about 150 g of force for 7 days, and histological changes of the periodontal ligament collected from various portions of the root were examined.
The histological architecture of the periodontal ligament, junction between cement and periodontal ligament, and junction between periodontal ligament and alveolar bone, especially in the area where Sharpey's fibers penetrate these parts, was examined by dividing the periodontal ligament into 4 portions, cervicomesial, cervicodistal, apicomesial, and apicodistal, and the architecture was compared before and after tooth movement. Microscopic observation revealed that, in the experimental group, collagen fibers of the periodontal ligament were thin without regular arrangement, while elastic fibers were increased. Electromicroscopic observation revealed three-dimensional changes in the ultra-microscopic structures of both collagen fibers and elastic fibers. It was also revealed that changes in Sharpey's fibers in the junctions were characterized by decreases in the number and diameter of fiber bundles, and this trend was more evident near the tooth neck than near the root apex, more evident on the oppression side than on the traction side, and more evident near the alveolar bone than near the cement.
These findings suggest that the architectural remodeling of matrix fibers and Sharpey's fibers in the periodontal ligament is a biological adaptation reflecting the distribution, directions and intensities of the forces inside the periodontal ligament.

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In order to develop an ammonia-free phosphate-bonded investment, Mg (H₂PO₄) ₂ nH₂O and MgO were used as a binder. The ratio (wt%) of MgO to Mg (H₂PO₄) ₂·nH₂O was designed from 3 to 0.5. Setting time and compressive strength were examined to determine a suitable distribution. A mixture with the ratio of 1.0 and 1.2 showed excellent properties as the binder. The setting time became shorter and compressive strength became lower as the ratio increased. X-ray diffraction appeared MgHPO₄·3H₂O after setting and Mg₂P₂O₇ after heated at 800°C. These results suggested that Mg (H₂PO₄) ₂·H₂O can be applied for dental investments.

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Three types of commercially available orthodontic bonding cements, a resin cement (SB) and two resin-modified glass ionomer (RMGI) cements classified as chemical-cured (FO) and light-cured (LC) types, were investigated to determine the setting time, amount of elements and mechanical properties. In addition, they were investigated to observe the powder particles and surface of the set cement.
The setting time of cements differed for each cement, with a range of 4-6 min, and LC showed the longest setting time. The Al/Si ratio of FO (0.68) was higher than that of LC (0.51), which may affect the setting behavior of RMGI cements. Backscattered electron images of the surface of the set RMGI cements demonstrated that smaller particles were filled heavily around the larger particles (10-20 μm). Resin structure separated from the matrix phase in the cement was observed in the surface of FO. The mechanical properties of RMGI cement regarding tensile and bending characteristics were significantly lower than those of SB. Lower elastic deformation revealed that RMGI cements were more brittle than SB. These properties may also affect the fracture type on the surface when brackets are debonded, and the removal property for residual cement from the surface.

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We evaluated the effects of glow discharge treatment (GDT) using an experimentally developed GDT device with alternating current for application to the bonding surfaces of dental prostheses. Tensile bonding tests were performed using resin luting cement containing a functional monomer (MDP) to four metals (cpTi, CoCr alloy, AgPd alloy and AgSn alloy) with and without GDT. Tensile bonding strengths to all metals treated with GDT increased significantly (p<0.05) compared to those without GDT. In addition, since the residual cement area on the fractured surface of the tensile specimens increased significantly (p<0.05) on the specimens with GDT for all cements, the fracture mode was apparently influenced by GDT. These results suggested that GDT was an effective technique for the surface treatment of dental prostheses to enhance bonding characteristics, even if the surface treatment effects were different among the tested metals. Furthermore, an effective decrease in the number of viable bacterial cells on the cpTi plate treated with glow discharge was shown by an in vitro detection assay of bacteria. SEM images on the specimens also demonstrated that the surface apparently became physically clean after GDT. We, therefore, expected that GDT was a promising surface treatment for cleaning and/or sterilizing dental prostheses.

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Partial anodontia is the term used when parts of the complete dentition are missing. There is a familial distribution of congenital absence of teeth in many instances, and heredity as an etiologic factor of importance has been generally accepted. We have experienced a familial case of partial anodontia in a mother and three daughters. In addition, we demonstrated orthodontic treatments of the eldest sister and youngest sister, who both have short roots of maxillary central incisors, ankylosis of labial frenum and diastema. Total number of missing teeth for the eldest sister and youngest sister is 13 and 14, respectively. A multibracket system was applied for the sisters with limited orthodontic treatment objectives. Even though the treatment objectives were limited, total period of active treatment for the eldest sister extended for more than 2 years. Moreover, the relapse of diasthema appeared after a short period of retension. Based upon the treatment result of the eldest sister, we tried to shorten the period of orthodontic treatment for the youngest sister. Her active treatment was shortened to 13 months, while her retention period was extended to 26 months. Fixed prosthodontic treatment was required for both sisters after orthodontic treatment. Long-term care was required for their occlusal rehabilitation, both orthodontically and prosthodontically.

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