• The Journal of the Korean dental association
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• v.11 no.5
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• pp.337-340
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• 1973

The authers have studied the marginal leakage on various filing materials : Composite resin, Polycarboxylate cement, Zinc phosphate cement, Silicate cement and Zinc-oxide eugenol cement, by means of penetration of 2% aquous methylene blue between cavity walls and filing materials at body temperature and at thermal changs in the range of 4~60℃ The results revealed as follows. 1) All the filling materials revealed the penetration of dye between cavity walls and filling materials. 2) Zinc-oxide eugenol cement was the most effective to prevent the dye penetration on the contrary silicate cement cases showed greatest leakage at 37℃ and at temperature changes in range of 4-60℃. 3) The composite resin showed moderate leakage either at 37℃ or at thermal changes 4) Marginal obstructions of polycarboxylate cement were unsatisfactory at 37℃ and at temperature changes.

• The korean journal of orthodontics
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• v.20 no.3 s.32
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• pp.583-591
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• 1990

If the bond strength is sufficient to resist orthodontic force, orthodontic brackets can be bonded to restorations. Orthodontic brackets were bonded to composite resin and glass ionomer cement restorations with no-mix adhesive or glass ionomer cement. The shear bond strength of adhesives bonded to restorations was studied in vitro. Orthodontic brackets were bonded to 10 extracted natural teeth, 40 composite resin restorations and 40 glass ionomer restorations. The surfaces of composite resin restorations were roughened or applied with bonding agent (Scothbond) after surface roughening. The surfaces of glass ionomer cement restorations were conditioned with acid etching or applied with Scotchbond to etched surface. The adhesive was no-mix resin or glass ionomer cement. The shear bond strength was measured. The results were as follows: 1. Orthodontic brackets could be bonded to composite resin restorations effectively as they could be bonded to acid etched enamel with no-mix adhesive. The shear bond strength was sufficient to resist orthodontic force and was not affected by bonding agent greatly. 2. The shear bond strength of no-mix adhesive bonded to acid etched glass ionomer cement restorations was sufficient to resist orthodontic force. However. the fracture risk of glass ionomer cement restorations was increased during debonding. The bonding agent couldn't increase the shear bond strength greatly. 3. The shear bond strength of glass ionomer cement bonded to glass ionomer cement restorations was lower than that of no-mix adhesive. The shear bond strength was sufficient to resist orthodontic force and was greatly decreased by bonding agent. 4. The shear bond strength of glass ionomer cement bonded to composite resin restorations was too low to resist orthodontic force.

• Journal of the Korean Institute of Educational Facilities
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• v.20 no.4
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• pp.35-43
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• 2013

Some results of experimental investigation conducted to assess the effect of cement composite strength and ductility on the shear behavior and crack-damage mitigation of stud connections between existing reinforced concrete frame in school buildings and seismic strengthening elements from cyclically direct shear tests are described. The cement composite strengths include 50 for medium strength and 70 MPa for high strength. Two types of cement composites, strain-hardening cement composite (SHCC) and non-shrinkage mortar, are used for stud shear connection specimens. The special SHCCs are reinforced with hybrid 0.2% polyethylene (PE) and 1.3% polyvinyl alcohol (PVA) fibers at the volume fraction and exhibits tensile strain capacity ranging from 0.2 to 0.5%. Test result indicates that SHCC improves the seismic performance and crack-damage mitigation of stud shear connections compared with stud connections with non-shrinkage mortar. However, the performance enhancement in SHCC stud connections with transverse and longitudinal reinforcements is less notable for those without additional reinforcement.

• Macromolecular Research
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• v.13 no.2
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• pp.120-127
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• 2005

Conventional poly(methyl methacrylate) (PMMA) bone cement has been widely used as an useful biopolymeric material to fix bone using artificial prostheses. However, many patients had to be reoperated, due to the poor mechanical and thermal properties of conventional PMMA bone cement, which are derived from the presence of unreacted MMA liquid, the shrinkage and bubble formation that occur during the curing process of the bone cement, and the high curing temperature ($above 100^{\circ}C$) which has to be used. In the present study, a composite PMMA bone cement was prepared by impregnating conventional PMMA bone cement with ultra high molecular weight polyethylene (UHMWPE) powder, in order to improve its mechanical and thermal properties. The UHMWPE powder has poor adhesion with other biopolymeric materials due to the inertness of the powder surface. Therefore, the surface of the UHMWPE powder was modified with two kinds of silane coupling agent containing amino groups (3-amino propyltriethoxysilane ($TSL 8331^{R}$) and N-(2-aminoethyl)-3-(amino propyltrimethoxysilane) ($TSL 8340^{R}$)), in order to improve its bonding strength with the conventional PMMA bone cement. The tensile strengths of the composite PMMA bone cements containing $3 wt\%$ of the UHMWPE powder surface-modified with various ratios of $TSL 8331^{R}$ and $TSL 8340^{R}$ were similar or a little higher than that of the conventional PMMA bone cement. However, no significant difference in the tensile strengths between the conventional PMMA bone cement and the composite PMMA bone cements could be found. However, the curing temperatures of the composite PMMA bone cements were significantly decreased.

• Smart Structures and Systems
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• v.18 no.2
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• pp.217-231
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• 2016

The present work aims to develop piezoresistive sensors of excellent piezoresistive response attributable to change in nanoscale structures of multi-wall carbon nanotube (MWNT) embedded in cement. MWNT was distributed in a cement matrix by means of polymer wrapping method in tandem with the ultrasonication process. DC conductivity of the prepared samples exhibited the electrical percolation behavior and therefore the dispersion method adopted in this study was deemed effective. The integrity of piezoresistive response of the sensors was assessed in terms of stability, the maximum electrical resistance change rate, and sensitivity. A composite sensor with MWNT 0.2 wt.% showed the lowest stability and sensitivity, while the maximum electrical resistance change rate exhibited by this sample was the highest (96 %) among others and even higher than those found in the literature. This observation was presumably attributed by the percolation threshold and the tunneling effect. As a result of the MWNT content (0.2 wt.%) of the sensor being near the percolation threshold (0.25 wt.%), MWNTs were close to each other to trigger tunneling in response of external loading. The sensor with MWNT 0.2 wt.% was able to maintain the repeatable sensing capability while sustaining a vehicular loading on road, demonstrating the feasibility in traffic flow sensing application.

• Computers and Concrete
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• v.4 no.2
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• pp.157-166
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• 2007

The paper considers a theoretical model to study sulfate ion diffusion in saturated porous media - cement based mineral composites, accounting for simultaneous effects, such as filling micro-capillaries (pores) with ions and chemical products and liquid push out of them. Pore volume change and its effect on the distribution of ion concentration within the specimen are investigated. Relations for the distribution of the capillary relative radius and volume within the composite under consideration are found. The numerical algorithm used is further completed to consider capillary size change and the effects accompanying sulfate ion diffusion. Ion distribution within the cross section and volume of specimens fabricated from mineral composites is numerically studied, accounting for the change of material capillary size and volume. Characteristic cases of 2D and 3D diffusion are analyzed. The results found can be used to both assess the sulfate corrosion in saturated systems and predict changes occurring in the pore structure of the composite as a result of sulfate ion diffusion.

• Restorative Dentistry and Endodontics
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• v.18 no.1
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• pp.103-113
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• 1993

The purpose of this study was to evaluate the tensile bond strength of composite resin inlays according to the their internal surface treatment and types of luting cement and compared them with the conventional direct resin filling thchnique. Class II cavities were prepared in 50 extracted human molar teeth, and then equally divided into five groups. Group 1 : Cavities of control group were directly filled with P-50. Group 2 : Cavities of resin inlay group were luted with resin cement. Group 3 : Cavities of resin inlay group were luted with luting G-I cement. Group 4 : Cavities of resin inlay group were luted with resin cement after sandblasting. Group 5 : Cavities of resin inlay group were luted with luting G-I cement after sandblasting. All specimens were polished with same method and stored in normal saline for 24 hours before testing. An Universal Testing machine(Model No. AGS-100A, Shimadzu, Japan) was used to apply tensile loads in the vertical direction, and the force required for separation was recorded with a cross-head speed of 5mm/min and 100kg in full scale. The results were as follows : 1. The mean tensile bond strength was lowest in group luted with luting G-I cement, with measurements of $14.45{\pm}0.78(kg/cm^2)$ and highest in group luted with resin cement after sandblasting, with measurements of $49.6{\pm}2.74(kg/cm^2)$. 2. The tensile bond strength was greater in resin inlay groups luted with resin cement than in control group and resin inlay groups luted with luting G-I cement(P<0.05). 3. The tensile bond strength was lower in resin inlay groups luted with luting G-I cement than in control group(P<0.05). 4. The tensile bond strength was greater in resin inlay groups luted with resin cement or luting G-I cement after sandblasting than without that(P<0.05).

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.487-501
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• 1998

In the case of CAD/CAM ceramic inlay restorations, if isthmus width is widened too much, it may cause fracture of remaining tooth structure or loss of bonding at the luting interface because of excessive displacement of buccal or lingual cusps under occlusal loads. So to clarify the criterior of widening isthmus width, this study was designed to test the tensile bond strength and bond failure mode between dentin and ceramic cemented with luting composite resin cements. Cylindrical ceramic blocks(Vita Cerec Mark II, d=4mm) were bonded to buccal dentin of 40 freshly extracted third molars with 4 luting composite resin cements(group1 : Scotchbond Resin Cement/Scotchbond Multi-Purpose, group2 : Duolink Resin Cement/ All-Bond 2, group3: Bistite Resin Cement/Ceramics Primer, and group4:Superbond C&B). Tensile bond test was done under universal testing machine using bonding and measuring alignment blocks(${\phi}ilo$ & Urn, 1992). After immersion of fractured samples into 1 % methylene blue for 24 hours, failure mode was analysed under stereomicroscope and SEM. Results: The tensile bond strength of goup 1, 2 & 4 was $13.97{\pm}2.90$ MPa, $16.49{\pm}3.90$ MPa and $16.l7{\pm}4.32$ MPa, respectively. There was no statistical differences(p>0.05). But, group 3 showed significantly lower bond stregnth($5.98{\pm}1.l7$ MPa, p<0.05). In almost all samples, adhesive fractures between dentin and resin cements were observed. But, in group 1, 2 & 4, as bond strength increased, cohesive fracture within resin cement was observed simultaneously. And, in group 3, as bond strength decreased, cohesive fracture between hybrid layer and composite resin cement was also observed. Cohesive fracture within dentin and porcelain adhesive fracture were not observed. In conclusion, although adhesive cements were used in CAD/CAM -fabricated ceramic inlay restorations, the conservative priciples of cavity preparation must be obligated.

• The Journal of Korean Academy of Prosthodontics
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• v.30 no.1
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• pp.93-101
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• 1992

The purpose of this study was to evaluate the effectiveness of core materials and luting agents on the retention of full veneer gold crown. The core materials used in this study was dental amalgam, and composite resin, and the luting agents were zinc phosphate cement, polycarboxylate cement, and glass ionomer cement. The obtained results were as follows. 1. In full veneer gold crown supported by composite resin core, the crown retention with zinc phosphate cement was the highest of all. 2. In full veneer gold crown supported by amalgam core, the crown retention was shown no statistical difference by luting agent. 3. There was no statistical difference in the crown retention between the full veneer gold crown supported by composite resin core and dental amalgam core.

• Restorative Dentistry and Endodontics
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• v.19 no.2
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• pp.409-428
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• 1994

Endodontic surgery is performed when conventional endodontic therapy fails or is contraindicated. In such cases, retrograde filling materials including amalgam, composite resin, and various cements have been used. Biocompatibilty and margin sealing ability of retrograde filling materials are important for the long term success of endodontic surgery. In vitro cell culture is frequently used as the method of measuring the biocompatibilty of dental materials. The purpose of this study was to evaluate the cytotoxicity of six kinds of retrograde filling materials including newly developed light curing glass ionomer cements. Each material was mixed according to. the manufacture's instruction and evaluated as : freshly mixed, 24-hour after mixing, and 168-hour after mixing respectively. The elution solution was extracted after 24-hour contact with materials using media. Cytotoxicity was evaluated by direct contact, or elution contact. Test results of radiochromium($^{51}Cr$) release, cell viability using tetrazolium dye (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl dimethyltetrazolium bromide(MTT) test and lactate dehydrogenase(LD) of damaged L929 cells were analyzed. In the $^{51}Cr$ release of direct contact, all experimental retrograde filling materials except amalgam and glass ionomer cement showed increased cytotoxicity compared to control. In the $^{51}Cr$ release of elution solution, the released $^{51}Cr$ was so minimal that it was impossible. to evlauate the cytotoxicity exactly. The elution solutions of glass ionomer cement and IRM showed marked cytotoxicity in MTT test. LD enzyme activity was highest in tests of direct contact with composite, light curing composite, and light curing glass ionomer cement and IRM. Amalgam revealed least cytotoxicity while IRM showed cytotoxicity using all three methods. Composite, light curing composite and light curing glass iomomer cement were cytotoxic in the tests of $^{51}Cr$ release and LD activity. Glass ionomer cement showed cytotoxic effect only in the MTT method. From these results it is suggested that the standardization and optimization of cytotoxicity testing, especially using elution solutions, should be strongly advised.