• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2003.10a
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• pp.15-15
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• 2003

치과재료에 사용되는 금속재료는 주로 스테인리스강, 타이타늄, Ni-Ti, Co-Cr등과 같은 특수합금이 주로 사용되고 있다. 이들 재료는 치과 보철물과 교정재료 및 충전재료로 주로 사용되고 있으며 그 외 치과에서 사용되는 기기나 기구에도 많이 활용되고 있다. 특히 치과 보철물을 사용하여 치료를 원하는 환자가 최근에 급격히 증가하면서 임플란트 고정체와 나사 등을 이용한 치료법의 연구와 개발이 필요하게 되어 세계적으로 연구와 투자가 활발히 진행되고 있다. 그러나 재료의 설계나 합금의 설계 및 제품의 설계상의 문제로 인하여 생체조직과 결합하는데 많은 문제점이 임상적으로 발생되고 있다. 즉 임플란트 표면의 생체적합성부여, 고정체와의 결합시 파절이나 풀림현상, 골에 고정체로 사용하는 나사의 강도와 내마모성문제 등이 개선되어야 할 문제점으로 남아있다. 또한 총의치에 사용되는 자석 어태치먼트의erosion-corrosion문제, 교정선의 탄성 과 마모저항문제 등은 앞으로 계속적인 연구를 행하여야할 과제로 남아있다. 또한 국소의치에서 사용되는 frame은 정밀주조법을 통하여 제조하며 주조상의 결함 등으로 인한 클라스프의 파절 문제점이 발생되고 있다. 따라서 본 연구에서는 치과재료로 사용되는 임플란트 고정체, 나사, 교정용 선등의 문제점을 고찰하고, 지금까지 이루어진 연구를 중심으로 최적의 개선 조건을 찾고자하였다. 최근첨단소재 및 금속재료를 사용하여 치과재료 합금을 설계할 수 있는 연구가 활발히 진행된다면 수입에 의존하고 있는 고가의 치과재료를 값이 싼 고성능의 제품으로 대체할 수 있는 효과가 클 것으로 생각된다.>$\rho$$\sub$0/=1.8 %. As t$\sub$Co/ increases, a transition from the regime of co-existence of superparamagnetic and ferromagnetic behaviors to ferromagnetic behavior was observed. Tunneling barrier called "decay length for tunneling" for the films having the thickness of Co layer from 1.4 to 1.6 nm was measured to be ranged from 0.004 to 0.021 ${\AA}$$\^$-1/.문에 기업간 관계를 연구하는 측면에서는 탐험적 연구성격이 강하다. 더 나아가 본 산업의 주된 연구가 질적이고 기업내부만을 연구했던 것에 비교하면 시초적이라고 할 수 있다. 또한 관계마케팅, CRM 등의 이론적 배경이 되고 있는 신뢰와 결속의 중요성이 재확인하는 결과도 의의라고 할 수 있다. 그리고 신뢰는 양사 간의 상호관계에서 조성될 수 있는 특성을 가진 반면, 결속은 계약관계 초기단계에서 성문화하고 규정화 할 수 있는 변수의 성격이 강하다고 할 수가 있다. 본 연구는 복잡한 기업간 관계를 지나치게 협력적 측면에서만 규명했기 때문에 많은 측면을 간과할 가능성이 있다. 또한 방법론적으로 일방향의 시각만을 고려했고, 횡단적 조사를 통하고 국내의 한 서비스제공업체와 관련이 있는 컨텐츠 공급파트너

• The Journal of the Korea Contents Association
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• v.13 no.9
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• pp.305-311
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• 2013

This study analyzed the oral status after recording the images by using QLF-D with targets of 38 youth people with hearing impairment and hearing language impairment. In order to investigate the state of oral hygiene, plaque index (O'Leary index) and contents of investigation of the state of the teeth included the number of sound teeth, the number of caries teeth, dental caries experience and the number of filling teeth. The following results were obtained. First, women lacked the management on plaque and had more caries teeth compared with men. In terms of impairment classification, subjects with both hearing and language impairment lacked the management on plaque and had more caries teeth. Second, subjects who did not get an oral exam for one year had more caries teeth. Oral hygiene score was the highest with the brushing time for 3-4 minutes. The number of sound teeth was increased as the brushing time was increased. In addition, the oral hygiene management time was the highest when cleaning the teeth, gums and tongue at the same time. Third, it was shown that the satisfaction of oral health education by using the new equipment was high. As a result of this study, in order to improve the oral health level of impaired students, they shall be trained to manage their teeth by themselves and educated to increase their motivation and practice. Thus, it is thought that various approaches which are differentiated from existing methods are required to be tried.

• Restorative Dentistry and Endodontics
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• v.25 no.1
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• pp.91-108
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• 2000

Most of cervical abrasion and erosion lesions show gingival margin where the cavosurface angle is on cementum or dentin. Composite resin restoration of cervical lesion shrink toward enamel margin due to polymerization contraction. This shrinkage has clinical problem such as microleakage and secondary caries. Several methods to diminish contraction stress of composite resin restoration, such as modifying cavity form and building up restorations in several increments have been attempted. The purpose of this study was to compare polymerization contraction stress of composite resin in Class V cavity subjected to cavity forms and placement methods. In this study, finite element model of 5 types of Class V cavity was developed on computer tomogram of maxillary central incisor. The types are : 1) Box cavity 2) Box cavity with incisal bevel 3) V shape cavity 4) V shape cavity with incisal bevel 5) Saucer shape cavity. The placement methods are 1) Incisal first oblique incremental curing 2) Bulk curing. An FEM based program for light activated polymerization is not available. For simulation of curing dynamics, time dependent transient thermal conduction analysis was conducted on each cavity and each placement method. For simulation of polymerization shrinkage, thermal stress analysis was performed with each cavity and each placement method. The time-temperature dependent volume shrinkage rate, elastic modulus, and Poisson's ratio were determined in thermal conduction data. The results were as follows : 1. With all five Class V cavifies, the highest Von Mises stress at the composite-tooth interface occurred at gingival margin. 2. With box cavity, V shape cavity and saucer cavity, Von Mises stress at gingival margin of V shape cavity was lower than the others. And that of box cavity was lower than that of saucer cavity. 3. Preparing bevel at incisal cavosurface margin decreased the rate of stress development in early polymerization stage. 4. Preparing bevel at incisal cavosurface margin of V shape cavity increased the Von Mises stress at gingival margin, but decreased at incisal margin. 5. At incisal margin, stress development by bulk curing method was rapid at early stage. Stress development by first increment of incremental curing method was also rapid but lower than that by bulk curing method, however after second increment curing final stress was the same for two placement methods. 6. At gingival margin, stress development by incremental curing method was suddenly rapid at early stage of second increment curing, but final stress was the same for two placement methods.

• Restorative Dentistry and Endodontics
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• v.36 no.2
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• pp.108-113
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• 2011

Objectives: To determine the effect of the spectral output of single and dual-peak light emitting diode (LED) curing lights on the microhardness and color stability of commercial resin composites formulated with camphorquinone and alternative photoinitiators in combination. Materials and Methods: Three light-polymerized resin composites (Z100 (3M ESPE), Tetric Ceram (Ivoclar Vivadent) and Aelite LS Posterior (Bisco)) with different photoinitiator systems were used. The resin composites were packed into a Teflon mold (8 mm diameter and 2 mm thickness) on a cover glass. After packing the composites, they were light cured with single-peak and dual-peak LEDs. The Knoop microhardness (KHN) and color difference (${\Delta}E$) for 30 days were measured. The data was analyzed statistically using a student's t-test (p < 0.05). Results: All resin composites showed improved microhardness when a third-generation dual-peak LED light was used. The color stability was also higher for all resin composites with dual-peak LEDs. However, there was a significant difference only for Aelite LS Posterior. Conclusions: The dual-peak LEDs have a beneficial effect on the microhardness and color stability of resin composites formulated with a combination of camphorquinone and alternative photoinitiators.

• Restorative Dentistry and Endodontics
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• v.36 no.2
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• pp.119-124
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• 2011

Objectives: The purpose of this experiment was to evaluate four different polishing systems of their polishability and polishing time. Materials and Methods: 4 mm diameter and 2 mm thickness Teflon mold was made. Z-250 (3M ESPE) hybrid composite resin was slightly overfilled and pressed with slide glass and cured with Optilux 501 for 40 sec each side. Then the surface roughness (glass pressed: control group) was measured with profilometer. One surface of the specimen was roughened by #320 grit sand paper and polished with one of the following polishing systems; Sof-Lex (3M ESPE), Jiffy (Ultradent), Enhance (Dentsply/Caulk), or Pogo (Dentsply/Caulk). The surface roughness and the total polishing time were measured. The results were analyzed with one-way ANOVA and Duncan's multiple range test. Results: The surface roughness was lowest in Pogo, and highest in Sof-Lex. Polishing times were shortest with Pogo, and followed by the Sof-Lex, Enhance and Jiffy. Conclusions: One-step polishing system (Pogo) is very effective to get the smooth surface in a short time, therefore it can be recommended for final polishing system of the restoration.

• Restorative Dentistry and Endodontics
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• v.33 no.5
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• pp.435-442
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• 2008

Type II root canal was defined that two canals leave the chamber and merge to form a single canal at short of the apex. The aim of this study was to analyse the master apical file (MAF) size according to various instrumentation techniques in the type II root canal when each canal was enlarged to working length. Eighty mesial roots of molar with ISO #15 initial apical file (IAF) size in type II root canals were randomly divided into four experimental groups with 20 teeth each. According to enlarging instruments, four groups are: K-$FLEXOFILE^{(R)}$ (KF), engine-driven Ni-Ti $P_{RO}T_{APER}{^{(R)}}$ (PT), HERO $Shaper^{(R)}$ (HS), $K^{3\;TM}$ (K3). All canals were enlarged to each working length with ISO #30 size: #30 in KF, F3 in PT, .04/30 in HS, and .06/30 in K3. The master apical file (MAF) size was confirmed by tactile sensation and universal test- ing machine (EZ test, Shimadzu Co., Kyoto, Japan). The mean MAF size was statistically compared using one-way ANOVA and Tukey HSD test at the 0.05 probability level. These results show that the MAF size was appeared one or two sizes larger than the final enlarging instrument when all canal in type II configuration were enlarged to each working length. Therefore, the clinician have to confirm the apical stop once more after instrumentation of type II root canal.

• Journal of the Korean Institute of Gas
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• v.17 no.5
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• pp.1-7
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• 2013

In this study, simulation work of HCNG refueling system was performed. The hydrogen was produced from steam reforming process by natural gas. The conversion of natural gas is increased as SCR is increased. but it was no significant difference more than 3 of SCR and fuel throughput is increased as GHSV is increased. Both conversion and fuel throughput levels was optimized when the $1700h^{-1}$ of GHSV. CNG was compressed from low pressure natural gas. For the mixing of $H_2$ and CNG is mixed with the high pressure conditions such as 400bar of $H_2$ and 250bar of natural gas. Single-stage compression was required more power than multi stage. So, multi stage compression was suggested for high pressure compression. We calculated the intermediate pressure to minimize total required power of compressors. The intermediate pressure for $H_2$ and natural gas were derived at 61 and 65 bar, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.133-140
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• 2016

The Ministry of Land, Infrastructure and Transport has introduced low-floor buses, which are convenient for passengers getting on and off the bus and for the handicapped. The standard bus model is 11 m long and uses compressed natural gas (CNG). However, this model has drawbacks in narrow rural road conditions such as those in farming and fishing villages and mountainous areas, as well as difficulty in refueling since CNG facilities are not readily available. In this study, running resistance values were obtained by coasting performance tests on actual roads using a Tata Daewoo LF-40 model with three different weight conditions: curb vehicle weight (CVW), half vehicle weight (HVW), and gross vehicle weight (GVW).The test methods include WHVC, NIER-06, and constant-speed driving at 60 km/h. These tests were used to measure the fuel economy of vehicles other than the target vehicles to obtain the combined fuel economy. The energy efficiency was highest in the case of CVW. In the WHVC mode, the fuel consumption rates of HVW and GVW were typically 3.5% and 12% higher than that of CVW, respectively. In constant-speed driving, the fuel efficiency of HVW was higher than that of CVW. Further research is required to analyze the exhaust gas data.

• Journal of the korean academy of Pediatric Dentistry
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• v.46 no.2
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• pp.158-164
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• 2019

The purpose of this study was to compare the bond strength of resin-modified glass ionomer (RMGI) to dentin with saliva contamination at different stages and using different decontamination procedures. Extracted human permanent molars were embedded onto acrylic resin with the dentin surface exposed. Group I was a control group that was conditioned with polyacrylic acid (PAA). Groups II and III were contaminated with saliva before PAA conditioning and Groups IV, V, and VI were contaminated with saliva after PAA conditioning. After saliva contamination, Groups II and IV were dried, Groups III and V were rinsed and dried, and Group VI was additionally conditioned with PAA. After surface treatment, the dentin specimens were filled with RMGI. Group I showed significantly higher bond strength than the other groups. Group VI showed a significantly higher bond strength than the other saliva contaminated groups. However, there were no significant differences in the failure mode between the different groups. Saliva contamination impaired the bond strength of RMGI to dentin, regardless of when the saliva contamination occurred. Decontamination with washing and drying could not improve the shear bond strength of RMGIC. When saliva contamination occurred after PAA conditioning, additional PAA conditioning improved the shear bond strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.573-582
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• 2021

In this study, a series of processes for evaluating the effective protection against barriers that should be equipped in institutions that perform reliability tests on high-risk ammunition, such as high-explosive ammunition, were introduced. The impact that high-explosive bombs can have on personnel includes damage to the eardrum and lungs caused by explosion overpressure and penetrating wounds that can be received by fragments generated simultaneously with the explosion. Therefore, a high-explosive with COMP B explosives as its contents were set up, and an explosion protection theory investigation to calculate the degree of damage, numerical calculations and simulations were performed to verify the protection power. A numerical calculation revealed the maximum explosion overpressure on the protective wall when the high-explosive exploded and the penetration force of the fragment against a 50 mm-thick protective wall to be 77.74 kPa and 41.34 mm, respectively. In the simulation verification using AUTODYN, the maximum explosion overpressures affecting the firewall and personnel were 56.68 kPa and 18.175 kPa, respectively, and the penetration of fragments was 35.56 mm. This figure is lower than the human damage limit, and it was judged that the protective power of the barrier would be effective.