• 대한치과보철학회지
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• 제38권2호
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• pp.226-241
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• 2000

Recently a new generation of crown and bridge veneering resins containing submicron glass fillers was introduced. These ultrasmall particle hybrid composite materials distinguish themselves, compared with conventional microfill crown and bridge resins, through improved mechanical properties. It is claimed that these composites are suitable for metal free crowns and even bridges using fiber reinforcement. The purpose of this study was to evaluate the effect of thermal cycling on the tensile strength of the following veneering composites: Artglass(Heraeus Kulzer Co., Wehrheim, Germany), Estonia(Kuraray Co.. Japan), Sculpture(Jeneric Pentron Co., Wallingford, U.S.A.), and Targis(Ivoclar Co., Schaan Liechenstein). According to manufacturer's instructions, rectangular tensile test specimens measuring $1.5{\times}2.0{\times}4.5mm$ were made using a teflon mold. Whole specimens were divided into two groups. One group was dried in a desiccator at $25^{\circ}C$ for 10 days, and another group was subjected to thermal cycling($10,000{\times}$) in water($5/55^{\circ}C$). All test specimens were placed in a universal testing machine and loaded until fracture with a crosshead speed of 0.5mm/min. Weibull analysis and Tukey's test were used to analyze the data. The fracture surfaces of specimens were observed in SEM and the aliphatic C=C absorbance peak of Estenia and Targis resin was analyzed using Fourier transform infrared(FTIR) spectroscopy. Within the limitations imposed in this study, the following conclusions can be drawn: 1. Both in drying condition and thermal cycling condition, the highest tensile strength was observed in Estenia testing group(p<0.05). 2. The strength data were at to single-mode Weibull distribution, and the Weibull modulus of all veneering composite resin specimens increased after thermal cycling treatment. 3. After thermal cycling test, the highest tensile strength was observed in the Estenia group, and the lowest value was observed in the Targis group. The tensile strength values showed the significant differences between each group(p<0.05) 4. The aliphatic C=C absorbance peak of Estonia and Targis resin was decreased after light curing, and there was no distinct change after thermal cycling.

• 대한치과보철학회지
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• 제44권5호
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• pp.654-664
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• 2006

Statement of problem: There has been a eat interest in the use of titanium for fixed and removable prostheses in recent because of its excellent biocompatibility. However, the melting temperature and chemical reactivity of titanium necessities casting system different from those used in conventional casting. The current titanium casting systems are based on an electric-arc design for melting the metal in an argon atmosphere and its exclusive investment. Despite the new development in Ti casting system, inadequate mold filling and internal porosity are frequently observed casting defects. Purpose : The purposes of this study were to compare the castibility and reaction layer of the casting titanium under the two casting machines and their investment condition. Material and method: coping and machine-milled titanium coping according to the casting methods and the marginal configurations. The total 28 specimens were used, and these are divided into 4 groups according to 2 casting machines and 2 investments. The castings were analyzed using x-ray microanalysis and microhardness testing. The reaction layer between margin of titanium casting and the investments was observed and analyzed with scanning electron microscope. Result: 1. Castabiliy of casting titanium specimen was best in the group of centrifugal casting machine and Selevest $CB^{\circledR}$ and good that of Selevest CB and pressure differential casting machine, Rematitan plus and centrifugal casting machine, Rematitan plus and pressure differential casting machine in order. 2. There was no significanct correlation in titanium castability in respect of casting machine. However ANOVA indicated that Selevest $CB^{\circledR}$ groups had significantly better castability than Rematitan $plus^{\circledR}$ groups.(p<0.05) 3. There was a significant microhardness difference between centrifugal casting machine groups and pressure differential groups.(p<0.05) Titanium castings in centifugal groups had significantly harder than those in pressure differential groups. 4. The addition of zirconia decreased interfacial reactivity. Conclusion: above result revealed that of the castability of titanium casting specimens had little correlation in casting machines and was better in magnesia-based investment contained ZrO2 groups. However in order to practice casting titanium in clininic, its castability should be improved, also there should be more research on factor of castability so that long-span prothesis and removable partial denture metla frame may be casted completly.

• 한국산학기술학회논문지
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• 제17권4호
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• pp.100-105
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• 2016

3D 프린터의 증가에 따라 대량 생산이 아닌 소량 제품의 빠른 개발 시간을 고려하여 3D 스캐너의 활용도 점차 증가하고 있다. 소량 생산 개발 트렌드뿐만 아니라 최근 자동차 및 전자부품의 제조업에 있어서도 정밀 부품의 개발 및 검사, 측정 등의 품질 문제가 중요한 이슈로 떠오르고 있다. 최근 3D 스캐너 장비 효율성 및 인식기술은 지속적으로 향상되었지만, 이에 반해, 이를 준비하는 스프레이 작업은 시간이 많이 걸리고 환경문제가 유발되기 때문에 제조업 제품 개발자들은 자동스프레이 도포 시스템 개발에 대해 지속적으로 요구해 왔다. 본 연구를 통해서 3D 스캔 준비 작업으로 필요한 스프레이 자동 도포 장비를 개발하였으며, 스프레이 도포 시 균일하게 미세 분말이 도포 될 수 있도록 파라미터 세팅에 대해 실험적으로 연구하였다. 결과적으로 빠르고 쉬운 자동 스프레이 도포 장비가 개발 되었고, 이를 활용해서 3D 측정을 위한 준비 시간이 기존 대비 1/10수준으로 단축되었다. 또한 다양한 조건에 대한 비교를 통해 최적의 도포 조건을 실험적으로 제시하였다.

• Restorative Dentistry and Endodontics
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• 제28권3호
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• pp.195-202
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• 2003

The purpose of this study was to evaluate the color changes of the composite resin resulting from xenon lamp exposure in different environments. Composite resin (Z 250 ; shade Al, A2, A3, A3.5, and A4) were applied in a cylindrical metal mold. Seventy five specimens according to environments of exposure were made as follows; Group I aluminum foiling of the specimens in the air at $37^{\circ}C$ for 1 day and 7 days. Group II : exposure of xenon lamp to the specimens in the air at $37^{\circ}C$ for 1 day and 7 days. Group III: exposure of xenon lamp to the specimens in distilled water at $37^{\circ}C$ for 1 day and 7 days. The color characteristics ($L^{*},a^{*},b^{*}$) of the specimens before and after exposure of xenon lamp were measured by spectrophotometer and the total color differences (${\Delta}E^{*}$) were computed. The results obtained were as follows : 1. In all groups except A1 shade of group III, the ${\Delta}E^{*}$ values presented below 2.0, and group III showed the highest ${\Delta}E^{*}$ values followed by group II and group I in a decreasing order(p<0.05). 2 In all shades and groups, the more the exposure time of xenon lamp and the lighter the shade were, the higher the tendency for discoloration (p<0.05). 3. The composite resins which was exposed to xenon lamp in the distilled water was more discolored than those in the air (p<0.05). 4. The major changes of composite resins which were exposed to xenon lamp in the air were an increase in yellowness through a positive shift of the $b^{*}$ value, and those in the distilled water were an increase in darkness and yellowness through a negative shift of the $L^{*}$ value and a positive shift of the $b^{*}$ value.

• Restorative Dentistry and Endodontics
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• 제22권1호
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• pp.358-373
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• 1997

Resin modified glass ionomers were introduced in 1988 to overcome the problems of moisture sensitivity and low early mechanical strength of conventional glass ionomers and to maintain their clinical advantages. The purpose of this study was to evaluate the color stability of four resin modified glass ionomers(Fuji II LC, Vitremer, Dyract and VariGlass), one resin composite material(Z-100), and one conventional glass ionomer(GC Fuji II) under several conditions. These conditions were as follows: 1) before curing, 2) after curing, 3) after polishing, 4) after 500 thermocycling, 5) after 1,000 thermocycling, 6) after 1,500 thermocycling and 7) after 2,000 thermocycling. Three specimens of each material/shade combination were made. Materials were condensed into metal mold with a diameter of 10 mm and a thickness of 2.0 mm, and were pressed between glass plates. The material was polymerized using a light polymerizing unit(Visilux II, 3M, USA). After removal of excess, the surface was polished sequentially on wet sandpapers. A reflection spectrophotometer(Model TC-6FX, Tokyo Denshoku Co., Japan) was used to determine CIELAB coordinates($L^*,a^*$ and $b^*$) of each specimen. CIE standard illumination C was used as the light source. The results were as follows : 1. In comparing different shades of same material, CIELAB color difference(${\Delta}E^*$) value was not significantly different from each other(p>0.05). 2. CIELAB color difference(${\Delta}E^*$) values between after-curing and after-polishing were ranged from 5.53 to 27.08. These values were higher than those of other condition combinations. 3. CIELAB color difference(${\Delta}E^*$) values between before-thermocycling and after-thermocycling were ranged from 1.40 to 7.81. Despite the number of thermocycling increased, CIELAB color difference(${\Delta}E^*$) value was low. 4. The color stability of resin modified glass ionomers was more stable than that of conventional glass ionomers but less stable than that of Z100.

• Restorative Dentistry and Endodontics
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• 제22권2호
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• pp.751-760
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• 1997

Resin-modified glass ionomers were introduced in 1988 to overcome the problems of moisture sensitivity and low early mechanical strengths of the conventional glass ionomers, and to maintain their dinical advantages. The purpose of this study was to evaluate the bi-axial fracture strength of four resinmodified glass-ionomers(Fuji II LC, Vitremer, Dyract, VariGlass), one resin composite material(Z-100), and one conventional glass-ionomer(Fuji II). Three specimens of each material and shade combination were made according to the manufacturers' instructions. Materials were condensed into metal mold with a diameter of 10mm and a thickness of 2.0mm and pressed between two glass plates. Resin-modified glass ionomers were polymerized using a Visilux II light curing unit by irradiating for 60 seconds from both sides, and conventional glass ionomer was cured chemically. After specimens were removed from the molds, surfaces were polished sequentially on wet sandpapers up to No. 600 silicone carbide paper. The specimens were thermocycled for 2,000 cycles between $5^{\circ}C$ and $55^{\circ}C$ distilled water. After thermocycling, bi-axial fracture strengths were measured using a compressive-tensile tester(Zwick 1456 Z020, Germany) with the cross head speed of 0.5mm/minute. The results were as follows: 1. Two factors of the kind and color of materials had a main effect on bi-axial fracture strength (p<0.01), and bi-axial fracture strength was influenced significantly by the kinds of materials (p<0.01). But there was no significant interaction between two variables of the kind and color of materials (p>0.05). 2. Comparing the mechanical properties of the materials, the elastic modulus of Z100 was higher than any other material, and there was no difference in the displacement at fracture among materials. The bi-axial fracture strength of Z100 was significantly higher than any other material, and that of resin-modified glass ionomers was significantly higher than that of conventional glass ionomer (p<0.05). 3. In the same material group, the color of material had little influence on the mechanical properties.

• 한국주조공학회지
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• 제11권6호
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• pp.475-481
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• 1991

In this study the fabrication technology and mechanical properties of AC8A/$Al_2O_3$ Composites by squeeze casting process were investigated to develope for application as the piston materials that require good friction, wear resistance, and thermal stability. AC8A/$Al_2O_3$ composistes without a porosity and the break of preform were fabricated at the melt temperature of $740^{\circ}C$, the preform temperature of $500^{\circ}C$, and mold temperature of $400^{\circ}C$ under the applied pressure of $1200kg/cm^2$ as the results of the observation of microstructures. As the results of this study, the tensile strength of AC8A/$Al_2O_3$ composites was not increased linearly with $Al_2O_3$ volume fraction and so it seemed not to agree with the rule of mixture, which had been used often in metal matrix composite. Also the tensile strength after thermal fatigue test was little different from that before the test. Consequently it was thought that AC8A/$Al_2O_3$ composites fabricated under our experimental conditions had a good thermal stability and subsequently a good interface bonding. Wear rate(i.e., volume loss per unit sliding distance) of AC8A/$Al_2O_3$ composites was decreased with $Al_2O_3$ volume fraction and the sliding speed at both room temperature and $250^{\circ}C$ and so there was a good correlation between wear rate and hardness. Also the wear rate of AC/8A20% $Al_2O_3$ composities was obtained the value of $1.65cm^3/cm$ at sliding speed of 1.14m/sec as compared with about $3.0\;{\times}10^{-8}cm^3/cm$ hyereutectie Al-Si alloy(Al-16%Si-2%Cu-1%Fe-1%Ni), which applied presently for piston materials. The wear behavior of $Al_2O_3$ composites was observed to a type of abrasive wear by the SEM view of wear surface.

• 박물관보존과학
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• 제4권
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• pp.23-32
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• 2003

경주 황남동의 통일신라시대 생활유적에서 출토된 철솥을 유리공방에서 사용된 도가니로 추정하고 있어, 이에 대한 과학적인 분석을 통해 철솥의 용도를 밝혀보기로 하였다. 우선 보존처리를 실시해 철솥의 원형을 찾아주고, 철솥 표면에 발생한 부식물 5점에 대해 SEM-EDS 분석 및 XRD 분석을 수행하였다. 철솥의 외형에 있어 도가니로 추정하는 데 가장 큰 역할을 했던 주구부분의 편이 보존처리 과정에서 발견되어 구연부는 완전한 상태로 복원되었다. 금속시편의 조직을 관찰한 결과 열처리없이 서서히 냉각시킨 주조철제로 밝혀졌다. 부식물의 성분원소는 Fe과 O를 주성분으로 한 P, Si, Ca, S 등으로서, 주요 구성 화화물은 quartz, vivianite, goethite, akaganeite, lepidocrocite, hematite 등이었다. 이와 같은 구성 성분들은 유리의 제조원료로서 이들이 철솥 외부표면의 부식물층에서 용융상태가 아닌 원료로 확인되었다는 것은 철솥이 출토된 유적이 유리제조와 관련된 공방지였다는 것을 알려주는 증거가 될 수는 있으나, 철솥이 유리 용융 도가니로 사용되었다는 증거가 될 수는 없다. 또한 철솥 출토 당시 우물지 안에 퇴적되어 있던 유기물 부식토와 사질점토 등을 고려해 보면 이들이 철솥의 부식물 형성인자로 작용한 것으로 볼 수도 있다. 따라서 철솥은 전형적인 주조철제로 도가니로 사용되지는 않은 것으로 결론지을 수 있다.

• 한국융합학회논문지
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• 제11권9호
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• pp.175-180
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• 2020

본 연구에서는 화물 운송 차량들을 모델링하였고 화물 운송 차량의 화물칸 및 윈드 디플렉터의 유무에 따른 유동해석을 수행하였다. Model A, B, C 모두, 100km/hr의 운행 속도를 기준으로 하여, 모델 형상의 윗부분에서 58m/에서 59m/s 사이로 가장 높은 유동 속도가 나타났다. Model A, B, C 세 모델들 모두 모델 형상의 앞부분에서 652Pa에서 671Pa사이에 공기저항의 압력이 가장 높게 나타났다. Model A의 최대 압력은 Model B 및 C에 비하여, 작게 나타나서, 속도에 대한 유동 저항이 가장 적게 작용한 것으로 사료된다. 따라서 Model A가 유류비 측면에서 공기 저항에 대한 유리한 조건을 가짐을 알 수 있다. Model C는 화물칸에서 급격하게 유동저항이 발생하는 Model B와 달리 유선형 형상의 윈드 디플렉터를 타고 공기가 조금 더 원활하게 흐르는 것을 확인할 수 있다. 따라서 각진 형상보다 유선형의 형상에서 공기저항 측면에서는 더 유리하다고 사료된다. 트럭 화물칸 및 윈드 디플렉터에 따른 운행중 공기흐름에 대한 해석 연구 결과를 적용함으로서, 본 연구가 실제적인 효율적인 설계와 미적인 융합에 적합하다고 보인다.

• Restorative Dentistry and Endodontics
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• 제30권4호
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• pp.327-334
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• 2005

본 연구에서는 ProFile로 근관형성 시 anticurvature filing 방법의 영향을 평가하고자 하였다 변형된 Bramante 법을 이용해 36개의 레진 블록을 치근단으로부터 8mm부위와 근관의 최대 만곡 부위에서 절단한 후 재조립하였다. 근관형성의 동작에 따라 anticurvature filing motion, circumferential filing motion, straight up-and-down motion의 3가지 실험군으로 분류한 다음 ProFile로 근관을 형성하였으며, 술 전$\cdot$후의 단면을 stereomicroscope로 촬영, 저장하고 중첩하여 근관 단면의 변화와 근관의 중심 이동률을 비교 평가하였다. 모든 위치에서 단면적 변화량, 만곡 내측으로의 형성량과 중심 이동률은 세 군간에 유의한 차이가 없었으며, 만곡 외측으로의 형성량은 치근단으로부터 8mm 부위에서 anticurvature filing motion, circumferential filing motion, straight up-and-down motion의 순으로 많았으나, 근관의 최대 만곡 부위에서는 차이가 없었다 이상의 결과에서 만곡 근관의 위험 부위에서 ProFile로 근관형성 시 anticurvature filing motion의 영향은 다른 motion과 비교해 볼 때 유의할 만한 차이가 없는 것으로 생각된다.