This study investigated ways to improve the mechanical properties of a dental glass polyalkenoate cement.Eight kinds of Aerosil, fillers which are included in composite resin and a round type of high molecular polyethylene were added to glass polyalkenoate dental cement.Specimens were created with various volumes of additives in the powder, then compressive strength, diametral tensile strength and flexural strength were tested.The results indicated that hydrophobic microparticles which were decreased the compressive strength of the cement.However, microparticles under 1μm in diameter increased the diametral tensile strength to control the volume.Fillers that had a polyhedron shape and a sharp edge increased flexural strength.

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We evaluated concentrations of postassium sulfate added to 2% glutarardehyde and 0.1% sodium hypochlorite solutions to decrease surface roughness of dental stone models caused by immersion in disinfectant solutions.Test results indicated that surface roughness(Ra)of dental stone models immersed in glutarardehyde and sodium hypochlorite solutions containing 1-5% potassium sulfate was decreased.In particular, the optimal concentration of postassium sulfate was two or three percent.

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Mechanical properties of recently developed resin-modified glass ionomer cements(RMGI)were compared with those of conventional acid-base glass ionomer(ABGI)cement.We studied three commercial RMGI cements and one ABGI cement as a control.Specimens for compressive, direct tensile, diametral, bending, fracture toughness measurement, and hardness measurement tests were prepared using the specific molds and stored in deionized water at 37℃ for 1 hour, 1 day, and 1 week prior to testing.ABGI was very brittle and fractured with little plastic deformation in each test.However, RMGI fractured after plastic deformation.Tensile, diametral tensile, and bending strengths of RMGI were significantly higher than those of ABGI.In addition, fracture toughness and critical energy release rate of RMGI were significantly higher than of ABGI.Hardness of RMGI increased with the increases in the duration of light exposure.These results indicated RMGI had a higher resistance to fracture than ABGI in the early stage after setting and that use of RMGI would be beneficial in applications involving restorative materials.

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Effect of the thickness of the adhesive layer between two Co-Cr alloy plates on mode I fracture toughness of dental adhesive resin was investigated varying the type of adhesive resin using a double cantilever beam(DCB)test.As adhesive resins typical of the soft and hard types, Super-Bond C&B(SB)and Panavia 21(PV)with filler were used respectively.The respective adhesive layers of the DCB test specimens were of 20, 100 and 200μm thick.The major findings were as follows.In case of SB, crack propagating areas in all test specimens were observed as cohesive failure, and those surfaces became remarkably rougher as the thickness of the adhesive layer increased.Fracture toughness also had a tendency to increase as the adhesive layer became thicker.Next, in case of PV, the fracture modes of the crack propagating area differed with the thickness of the adhesive layer, such as interface failure at 20μm thickness, and cohesive fracture at 100 and 200μm thickness.The cohesive fractures were observed as similar flat surfaces.Therefore, regarding fracture toughnesses, there was no difference due to the thickness of the adhesive layer between 100 and 200μm thickness, however, at 20μm thickness, it was found that the fracture toughness decreased somewhat.

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Ti and HA-G-Ti composite with and without electrochemical surface-modification were applied to bone morphogenetic protein(BMP)carrier.Eight kinds of specimens associated with substrate, surface-modification, and BMP were implanted in the femora of Japanese rabbits.At 3 weeks after implantation, new bone formation was quantitatively analyzed by computer-area analysis through Ca concentration map of the sectioned bone and qualitatively evaluated by histological observation and micro-Fourier transform infrared spectroscopy(FTIR).New bone formation in the specimens with BMP were observed in the whole area of bone marrow, whereas those without BMP were observed only around the specimen.The amount of new bone formation in the former was about twice as much as that in the latter.Effect of the substrate and electrochemical surface-modification on the induction amounts of new bone was not clarified.Photomicrograph revealed that the new bone around the specimen was sound and there was no remarkable difference in the bone tissues between 8 kinds of specimens.FTIR spectrum of the new bone was similar to that of original cortical bone, indicating carbonate containing apatite with collagen.These results suggested that the additing BMP to the specimens strongly accelerated new bone formation in bone marrow.

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Mixing of dental stone was examined using a new planetary mixing machine and two vacuum blade-driven mixing machines under different conditions.The following results were obtained.(1)Setting expansion and compressive strength were obtained using the planetary mixing machine.Increased rotational power resulted in a reduction in setting time.The lowest power used in the planetary mixing machine produced physical properties similar to those obtained with blade-driven mixing machines.(2)Formation of di-hydrate was closely related to setting expansion and compressive strength.(3)The planetary mixing machine is useful for mixing dental stone.

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This study evaluated the impact resistance of tooth-colored restorative materials bonded with resin cements.Different types of restorative materials such as ceramics and resins for crown and bridge were bonded to stainless steel or bovine tooth using various cements, then examined with an HK-impact testing machine.Factors affecting impact resistance were investigated.Resin cements effectively improved impact resistance.For dentin, there was a significant positive correlation between impact fracture energy and shear bond strength.Restorative material with higher resilience showed excellent impact resistance.The impact fracture energy increased with increases in elastic modulus of the substrate.For stainless steel and enamel, composite resin cements with high elastic modulus were superior.However, for dentin, PMMA resin cement with low elastic modulus was superior.In the case of composite resin cement, the fracture energy after thermal cycling did not vary, while in the case of PMMA resin cement, it was decreased significantly.

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The quick heating technique has a great advantage in casting procedures, therefore, several products made of not only gypsum-bonded investments but also phosphate-bonded investments are available on the Japanese market.In this study, properties, such as fluidity, setting expansion, thermal expansion, surface roughness and powder particle size distribution of phosphate-bonded investments for quick heating casting were compared with those of conventional phosphate-bonded investments.There were only a few differences between properties obtained from quick heating investments and those obtained from conventional investments, with the exception of carbon presence for conventional investments and slight differences in powder particle size distribution among these investments.

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Granule types of resorbable bio-active glass(R-BAG) and resorbable hydroxylapatite(R-HA) were examined during bone remodeling in vitro and in vivo.R-BAG and R-HA did not show any cytotoxic effect on cultures of osteoblasts(OB) and peripheral bloodlymphocytes/monocytes(PBL).Higher alkaline phosphatase(ALPase) activity was shown in OB cultured with R-RAG than in those culture with R-HA and ALPase positive cells were recognized specifically around granules of R-BAG.The number of osteoclasts(OC) derived from PBL was suppressed by R-BAG, although OC formed from PBL cultured with R-HA were the same as control PBL.When R-BAG were inoculated into jaw bones of rats, fissures were observed specifically in R-BAG and bone formation was recognized inside the R-BAG.When 10 patients each were inoculated with R-BAG or R-HA respectively after extraction of a tooth, bone remodeling was recognized at the area inoculated with R-BAG after an average 4.7 months and after an average 9.2 months with R-HA.

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