• The Journal of Korean Academy of Prosthodontics
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• v.45 no.2
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• pp.191-202
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• 2007

Statement of problems: Long-term success of esthetic restorations, depends on various factors, especially on color stability of the restorations. The color stability is affected by resin cements beneath the porcelain laminate veneers. Purpose: The purpose of this study was to comprehend the color stability of resin cements by comparing with 4 different kinds of resin cements (Choice, Variolink II, Nexus 2, Rely-X). Material and methods: Porcelain laminate disk samples were luted with resin cements. After thermocycling of each 1000, 2000 and 3000 cycle, specimens were measured by spectrophotometers and the color differences were. Results: 1. After thermocycling of 1000, 2000 and 3000cycle, color difference, $({\Delta}E^*)$ of all specimens were incresed, but were not statiscally significant differences. 2. In the Choice of A1 shade and the Nexus 2 of A3 shade, color difference$({\Delta}E^*)$ after thermocycling of 3000cycle was $incre^*ased$ significantly than after thermocycling of 1000cycle. However, other groups did not show any statistically significant differences (P<0.05). 3. After thermocycling of 3000cycle, color difference$({\Delta}E^*)$ between A1 shade and A3 shade of Nexus 2 showed statistically significant difference. However no statistically significant differences were observed in other groups (P<0.05). 4. The mean of color difference$({\Delta}E^*)$ is 1.0-2.06 after 3000 thermocycling and the data were ranked in the ascending order of Variolink II, Nexus 2, Choice and Rely-X in A1 shade group and Choice, Rely-X, Variolink II and Nexus 2 in A3 shade group. Conclusion: Above results revealed that, after 3000 thermocycing, the color difference $({\Delta}E^*)$ of experimental resin cements was within clinically acceptable ranges. Color stability of 4 different resin cements was comparatively excellent.

• Journal of the korean academy of Pediatric Dentistry
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• v.47 no.2
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• pp.196-204
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• 2020

The aim of the study is to compare the fluoride release and recharge properties of glass ionomer cements and 'alkasite'. Specimens of two glass ionomer cements (Fuji IX GP and Riva Self Cure), 'alkasite' restorative material (Cention N) and composite resin (Filtek™ Z350XT) were prepared. The fluoride release of each specimen was measured for 28 days. Thereafter, 1.23% acidulated phosphate fluoride (APF) gel was applied to experimental groups. No treatment was performed on control groups. The fluoride release was measured for additional 7 days to evaluate the fluoride recharge properties of each materials. The fluoride release was highest in Riva Self Cure, followed by Fuji IX GP, Cention N (p < 0.05). Fluoride release of Cention N was measured to be approximately 49% of Fuji IX GP's. After the application of 1.23% APF gel, increases in fluoride release were observed in Riva Self Cure, Fuji IX GP and Cention N (p < 0.05). Fluoride recharge was observed in Cention N as well as in glass ionomer cements. Further studies are required to evaluate the anti-cariogenic properties of Cention N at clinical conditions.

• Journal of the Korea Institute of Building Construction
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• v.11 no.3
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• pp.247-255
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• 2011

Currently, there is database for per unit requirements of major construction materials in terms of energy consumption and $CO_2$ emission based on the input-output table published by the Bank of Korea in 2000, but no database for per unit requirements based on input-output tables was published in 2005 and 2007. The purpose of this study was to calculate the unit requirement values of major construction materials in terms of energy consumption and $CO_2$ emission generated by using the input-output tables published in 2005 and 2007. To estimate the unit requirement values, a database building method with the input-output tables was adopted by selecting 16 types of construction materials in wide use on construction sites. When the study results were compared with existing unit requirement values based on the input-output table of 2000, there were small discrepancies, from which it can be interpreted that the method used in the study is reasonable. Unit requirement values estimated based on input-output tables of 2005 and 2007 tended to decrease, and the highest value of energy consumption and $CO_2$ emission were found in the materials using cement and rebar.

• Restorative Dentistry and Endodontics
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• v.21 no.1
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• pp.202-217
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• 1996

The purpose of this study was to compare the degree of microleakage of Glass-Ionomer root canal sealer possessed several enviable properties with that of the other sealers and to evaluate clinical performance. One hundred twenty single-rooted teeth were used in this experiment. The teeth were cleaned mechanically and immersed for 24 hours in 5.25% sodium hypochlorite and clinical crowns then were removed. After the root canals were instrumented using a step-back technique. one hundred twenty single-rooted teeth were divided into five groups of 24 in each. Group 1 : Tubli-Seal(Kerr Co., MI, U.S.A/ZOE-based), lateral condensation Group 2 : Sealapex(Kerr/Sybron, Romulus, MI/ $Ca(OH)_2$-based), lateral condensation Group 3 : AH 26(De Trey Co., Zurich Switzerland/Resin-based), lateral condensation Group 4 : Ketac-Endo(ESPE GMBH & CO. KG Seefeld:oberbay. Germany/ Glass Ionomer Cement-based), lateral condensation Control group : no sealer. lateral condensation And then. the root canals were obturated by lateral condensation technique with gutta-percha and experimental sealers. The control group were obturated without sealer. The teeth were placed in a vacuum chamber for 15 minutes and immersed 2% methylene blue under vacuum for 15 minutes. The teeth were passively stained for 1 week and 2 weeks and were cleared and evaluated for linear dye leakage using Tool maker's microscope(${\times}200$). The results were as follows: 1. There were statistically significant differences in the degree of dye penetration between the control group and experimental groups(p<0.05). 2. In the experimental groups, Sealapex($1.2871{\pm}0.9180mm$) exhibited the lowest mean value of dye penetration, followed by Ketac-Endo($1.4432{\pm}0.8082mm$), AH 26($1.5030{\pm}0.7752mm$) and Tubli-Seal($1.6458{\pm}1.0292mm$)(p>0.05). 3. There were statistically significant differences in the variation of microleakage between 1 week and 2weeks in Tubli-Seal and Seal apex groups (p<0.05). 4. The degree of dye penetration of all groups were increased as the time elapsed and AH 26 showed the lowest variation(+0.11) and Tubli-Seal(+ 1.03) showed the highest variation (p<0.001).

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.533-549
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• 2017

In this study, drainage systems were proposed to drain the leakage of groundwater in the existing underground concrete structures. The system consists of drainage board, wire mesh, fixed nail, and mortar with mineral. In order to increase constructability, the drainage board and wire mesh were attached on the surface of cement concrete using the air nailer and fixed nail. The mortar with 30% of blast furnace slag was sprayed on the drainage board and wire mesh using the spray mortar equipment. The field test construction was carried out in a conventional concrete lining tunnel and concrete retaining wall for performance verification of the drainage system in the field. There was no problem with performance degradation in the drainage system for three years after construction. The bond strength tests were performed on the sprayed mortar at 14 days and about 3 years after field test construction. In case of attaching the wire mesh on the drainage board, the bond strengths of the sprayed mortar were 1.04 MPa at 14 days and 1.46 MPa about 3 years. In case of the drainage board without the wire mesh, the bond strengths of the sprayed mortar were 1.13 MPa at 14 days and 0.89 MPa, less than 1 MPa of bond strength criteria, about 3 years.

• Restorative Dentistry and Endodontics
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• v.32 no.5
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• pp.403-410
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• 2007

The purpose of this study was to investigate whether rhBMP-2 (BMP2) could induce synergistic effect with $Pro-Root^{(R)}$ MTA (MTA) in pulpotomized teeth in the rats. Healthy upper first molars from thirty-two, 10 weeks old, Sprague-Dawley rats were used for this investigation. The molars were exposed with round bur, and light pressure was applied with sterilized cotton to control hemorrhage. 1.2 grams of MTA cement was placed in right first molars as a control group. In left first molars, $1\;{\mu}g$ of BMP2 was additionally placed on exposed pulps with MTA. All cavities were back-filled with light-cured glass-ionomer cements. The rats were sacrificed after 2 weeks and 7 weeks, respectively. Then histologic sections were made and assessed by light microscopy. Data were statistically analyzed via student t-test with SPSSWIN 12.0 program (p < 0.05). Inflammation observed in 2 weeks groups were severe compared to the 7 weeks groups. But the differences were not statistically significant. BMP2-addition groups had less inflammation than MTA groups in both periods, though these differences were also not statistically significant. In conclusion, the combination of BMP2 and MTA showed no differences with MTA only for pulpotomy of rat teeth.

• Journal of the Korea Institute of Building Construction
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• v.12 no.3
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• pp.275-283
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• 2012

Nitrite-type hydrocalumite (calumite) is a material that can adsorb the chloride ions ($Cl^-$)that cause the corrosion of reinforcing bars and liberate the nitrite ions ($NO_2{^-}$) that inhibit corrosion in reinforced concrete, and can provide a self-corrosion inhibition function to the reinforced concrete. In this study, VA/E/MMA-modified mortars with calumite were prepared with various calumite contents and polymer binder-ratios, and tested for corrosion inhibition, chloride ion penetration, carbonation and drying shrinkage. As a result, regardless of polymer-binder ratio, the replacement of ordinary Portland cement with hydrocalumite has a marked effect on the corrosion inhibiting property of the polymer-modified mortars. However, chloride ion penetration and carbonation depths are somewhat increased with higher calumite content, but can be remarkably decreased depending on the polymer-binder ratios. The 28-d drying shrinkage shows a tendency to increase with the polymer-binder ratio and calumite content. VA/E/MMA-Modified mortars with 10 % calumite did not satisfy KS requirements. Accordingly, a calumite content of 5 % is recommended for the VA/E/MMA-modified mortars with calumite.

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.347-354
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• 2013

Recently, crushed fine aggregates are being widely used due to the shortage of natural sand. In Korea, the amount of fine particles under 0.08 mm contained in crushed fine aggregates is restricted to be less than 7%, which is similar to the regulations of ASTM but is still very strict compared to the regulations of the other nations. In addition, the crushed aggregates already have in them about 20% of fine particles under 0.08 mm which occurs while they are crushed. The fine particles are not easy to wash out, and also to maximize the use of resources it is deemed necessary to review the possibility of enhancing the limit of the amount of fine particles. Therefore, this study conducted experiments to analyze the characteristics of fine particles under 0.08mm and their influence on the properties of concrete. Experiments using silt and cohesive soil were also done for comparison. In the experiments on fine particles, the methylene blue value was more in the soil dust contained in silt and cohesive soil than in the stone powder contained in crushed fine aggregates. Also, the methylene blue value had a close correlation with packing density and liquid & plastic limit. In the experiments done with concrete, the quantity of high range water reducing agent demanded to obtain the same slump increased as the fine particle substitution rate heightened. However, in the experiment which used stone powder testing the compressive strength and tensile strength of concrete in the same water-cement ratio, there was little change in strength with less than 20% addition of fine particles among the fine aggregates, and no meaningful difference in the amount of drying shrinkage of concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.7-14
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• 2015

The aim of this research is suggesting dry processed bottom ash as a new and economical source of lightweight aggregate for mortar and concrete. The dry process of bottom ash is an advance method of water-free and no chloride because only cooled down by double dry conveyer belt systems. Furthermore, because of relatively slow cooling down process helps burning up the remaining carbon in bottom ash. Using this dry process bottom ash, to evaluate the feasibility of using as a lightweight aggregate for mortar and concrete, two-phase of experiments were conducted: 1) improving shape of the bottom ash, and 2) controlling grade of the bottom ash. From the first phase of experiment, additional abrasing process was conducted for round shape bottom ash, hence improved workability and compressive strength was achieved while unit weight was increased comparatively. Based on the better shape of bottom ash, from the second phase, various grades were adopted on cement mortar, standard grade showed the most favorable results on fresh and hardened properties. It is considered that the results of this research contribute on widening sustainable method of using bottom ash based on the dry process and increasing value of bottom ash as a lightweight aggregate for concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.442-449
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• 2017

In this study, a method to inject small amount of activation agent from the outside of the pipeline to the inside wall of the pipe was newly proposed to enhance pumping efficiency of cementitious materials. The activation agent is injected into the slip-layer, which is generally formed in the vicinity of the inside wall of the pipe during pumping cementitous materials. Through the injections, it is expected to decrease viscosity of slip-layer, namely, the friction between the mateirals and the pipe. The proposed method was verified by lab-scale pumping tests with mortars having water to cement ratio of 47%. The tests were performed with two different type of activation agents(superplasticizer and anionic surfactant) and three different amount of the agents(0.14, 0.28, 0.42% of the mortar volume). The compressive strength were measured with and without injecting the activation agent, and the internal pressures of pipeline were measured. When the anionic surfactant was used, there was no change in the compressive strength. As the amount of anionic surfactant increased, the pumping pressure decreased up to 71.4% at the maximum.