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Electronic industry makes constant effort to replace the Pb bearing solder with the lead-free solder, because of the growing tendency of being intensified the environmental regulation of the use of lead. It is not yet classified for the evaluation method of mechanical properties such as the shear strength for the lead-free solder paste. Solder joint was made in this research by reflow method with the solder paste Sn-3.0Ag-0.5Cu. In order to standardize the shear test method, the shear strength of solder joint of 2012 ceramic chip was measured at the shear speed of 25 mm/min using with the various shapes of shear jigs. The optimum number of shear test specimens was statistically analysed by the calculation of accumulation average value, standard deviation, and the width of confidence interval. The suitable range of jig height on the ceramic chip was obtained by testing with various location of jig. The fracture surface of solder joint was analysed using by SEM.

keyword : Standardization, Shear test, 2012 Ceramic chip, Lead-free Solder paste

The thermoelectric properties of ReSi(1.73+x)Al(0.02) (-0.02 < × < 0.04) have been investigated in the temperature range between 323 and 1073 K. As a result of Al-addition, the electrical properties of the ternary at low temperatures are changed from the character of nondegenerate semiconductors, which is of binary ReSi(1.75), to that of degenerate semiconductors, and the band-gap along [001] becomes wider than that of the binary. The variation of Si composition affects the electrical properties along [100], but those along [001] are conserved. The change of the band structure due to the variation of Si composition is estimated with the result of the Seebeck coefficient at low and high temperatures. The maximum dimensionless figure of merit (ZT) along [100] is about 0.7 in the temperature between 473 and 773 K and along [001] is 0.67 at 1073 K.

keyword : ReSi(1.75), Thermoelectric properties, Seebeck coefficient, Electrical resistivity, Single crystal

Porous and bioactive composite scaffolds were successfully fabricated by salt leaching method using poly ε-caprolactone (PCL) and hydroxyapatite (HA). The scaffolds have interconnected pore structure with pore size ranging from 200 to 230 ㎛. The pore size of pure PCL scaffolds and PCL/HA scaffolds was similar to that of the salt particles (200-300 ㎛). However, the porosity and the pore size of the PCL/HA composite scaffolds slightly decreased as the HA concentration increased. In addition, the pore walls became thick and the small pores decreased, and consequently the interconnectivity of the pores decreased. The cell viability and response of the scaffolds were assessed by MTT assay. The biological assessment results showed that HA content did not affect initial cell attachment in both scaffolds with and without HA. The osteoblasts proliferated in both types of the scaffolds, but the cell number was higher in the PCL/HA composite scaffolds. It was clearly demonstrated that the incorporation of hydroxyapatite enhances bone cell proliferation rather than initial cell attachment in PCL/HA composite scaffolds. Combining HA and biodegradable polymer could be applicable to bone scaffolding materials.

keyword : Scaffold, Hydroxyapatite, Cell proliferation, Biodegradable polymer, Osteoblast

The mineralized collagen fibrils and tablet-like crystals were observed in the murine femoral trabecular bone, which appeared to have more of a random arrangement with the crystal orientation changed within an approximately 100 nm. The presence of the continuous (002) ring indicates that the c-axis of crystals is mostly parallel to the section and the directions of the c-axis are relatively random with no preferred orientation. The distribution and orientation of mineral apatites in the murine trabecular bone was found to be different from those typically observed in the lamellar bone and the difference can be attributed to the more complex local stress state in the trabecular bone. It was also shown from dark field image analyses that apatite crystals are not single crystalline, but multi-crystalline. This observation is compatible with the suggestion that the formation of a large platelet was attained by joining independent nuclei. The small round crystalline particles (2 nm in size with the lattice fringe lines of 0.28 nm in spacing) observed near or at tip of collagen fibrils were likely to be apatite nuclei nucleated independently. A small misorintation angle between adjacent nuclei can be linked with the multi-crystallinity of apatites observed in the present study.

keyword : femoral trabecular bone, Mineral apatite, Amorphous calcium phosphate, Apatite, SBF, simulated body fluid

The purpose of this study was to investigate the fatigue fracture phenomena of clinically used dental Ni-Ti alloy files. ProTaper(R)(Maillfer, Dentsply, Ballaigues, Switzerland) were used, respectively, for experiment. In order to observe the fatigue surface of clinically used file, the fractured files were classified into three groups: fractured files at the upper, middle and lower part after clinical use. The fractured surface and chemical composition were studied with energy dispersive X-ray spectroscopy(EDS) and field emission scanning electron microscope(FE-SEM) to analyze elements on the surface of fractured file. Fatigue fracture crack of Ni-Ti file was initiated and propagated at defects such as scratch formed by machine under repeated load. Fractured surface of Ni-Ti file showed the brittle fracture behavior at the exterior and ductile fracture behavior at the interior of specimen. The ductile fracture behavior appeared predominantly at the lower part of Ki-Ti file compared with at the upper part of Ni-Ti file.

keyword : Fatigue Fracture, Dental Ni-Ti Alloy Files, Brittle Fracture, Ductile Fracture

The aim of this investigation was to analyze surface of clinically failed dental implant fixture in order to determine possible causes of failure. The failed implants were classified into three groups; 3 and 5 month used implant, 19 and 60 month used implant, and fractured implant, after implantation for 33 month and 120 month in patient jaws. The topography and surface chemical composition were studied with energy dispersive x-ray spectroscopy(EDS) and field emission scanning electron microscope(FE-SEM) to analyze elements on the surface of flank and bottom of thread. Evaluations were performed at the upper, middle and lower implant fixture. From surface observation of 3 and 5 month used implant, contaminants were detected in the middle and lower part of implants. Overall, foreign elements such as silicon, carbon, oxygen, zinc, sulfur, zirconium, and chloride were detected in failed implants. From surface observation of 19 and 60 month used implant, the corrosion was accelerated at the bottom of thread that was accumulated chloride. Corrosion products showed in the bottom of thread including dissolution elements, such as Au, Cu, Ag, from suprastructure of dental implant system. From surface observation of fatigue fractured implants, the crack were nucleated in the bottom of thread and the crack of corrosion fatigue was predominantly propagated. The corrosion products including chloride were found opposite side of starting point of corrosion fatigue crack. We could find the fatigue striation and estimate the dimple fracture of implants.

keyword : Failed Dental Implant Fixture, Suprastructure, Fatigue Fractured Implant

Silver is one of the most universal antimicrobial substances. Nano-technogy enables us to expand the surface area of silver particles markedly. Silver nano-particles were successfully produced less than 10 nm in size. Nanosilver showed excellent antibacterial activities against Salmonella typhi and Pseudomonas aeruginosa around 1 ppm and Mycobacterium tuberculosis around 10 ppm. Nanosilver induced the severe morphologic changes in cell wall and cytoplasm of bacteria. Antimicrobial mechanisms of nanosilver were different according to the species of bacteria; plasmolysis in Salmonella typhi and metabolic disturbance due to ingestion of nanosilver in M. tuberculosis. To confirm the toxicity of nanosilver, four groups of mice (60 mice in total) have been fed with nanosilver suspension (0, 10, 30, 100 ppm) for 6 months. Their behaviors, weight changes and hematologic findings of mice after feeding of nanosilver showed similar results with those of the control although the mice had been fed 100 ppm of nanosilver for 6 months. From the results, silver nanoparticles probably will be available as a good and safe antibiotic alternative.

keyword : Nanosilver, Antimicrobial mechanism, In vivo study

The main cause of re-operation in patients who received total hip arthroplasty is wear debris-mediated osteolysis in bone-implant interface. Recently, alumina or zirconia ceramic hip joint have also become available. Therefore, Al2O3 particles induced cytotoxicity on osteoblast-like MG-63 cells and osteoclastlike Raw 264.7 cells was observed through in vitro and in vivo study. Low concentration of Al2O3 powders did not induce cytotoxicity, however the proliferation of osteoblast cultured with high concentration of Al2O3 powders were significantly inhibited. Al2O3 particles were also observed on the surface and inside the MG-63 and Raw 264.7 cells accompanied with the morphological changes of cytoplasmic organelles. Al2O3 particles injected in subcutaneous tissue of rats did not induce inflammatory response.

keyword : Al2O3 Particle, Osteoblast, Osteoclast, Viability, Morphologic change

We report on advanced β-titanium alloys having excellent biocompatibility without containing V or Al that has been known as a toxic element for human body, and on a low elastic modulus to be used in the fields of artificial joint and dental implant in the replacement of natural human bone. Ternary Ti-Nb-Si alloys consisting of biocompatible alloying elements have been produced to investigate the alloying effect on microstructure, elastic modulus and mechanical properties. On the basis of experimental results obtained, it is suggested that Si has an effective role to suppress the formation of ω-phase leading to reduction in elastic modulus.

keyword : β-titanium alloy, Biocompatibility, Ti-Nb-Si, Low elastic modulus, Martensite, ω-phase

In order to examine the influence of variation in grain size and microstructure on mechanical properties of Co-29Cr-6Mo alloy for biomedical implant materials, the tensile properties and the dry friction wear characteristics of the forged Co-29Cr-6Mo alloy without Ni and C addition were investigated. The microstructure of as-forged alloys, consisting of fcc phase mixed with athermal hcp martensite, is found to become finer as the increasing of forging ratio. The hot-forging process for fabricating the fine microstructure with different grain sizes of 43, 11 and 3 ㎛ has been successfully established under the condition that forging temperature of higher than 1273 K is strictly kept during forging. The tensile properties, such as the yield stress, the tensile stress and the elongation, are improved with decreasing the grain size and thereby increasing the volume fraction of the fcc phase in the microstructure. Worn surfaces are hardened during the wear tests, forming oxide films. This results from significantly high work hardening rate of the forged alloy, caused by the strain-induced martensitic transformation from an fcc-γ phase to an hcp-ε phase, which contributes to the improvement in the dry wear resistance. Wear mechanisms of the forged alloy are discussed on observations of the wear scars formed on the alloy disc and the alumina ball surfaces. It is suggested that a delamination wear resulting from the fatigue fracture likely occurs under the present dry wear condition.

keyword : Co-Cr-Mo alloy, Forging, Stacking fault energy, Work hardening rate, Strain-induced martensitic transformation, Dry friction wear