• The Journal of Korean Academy of Prosthodontics
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• v.54 no.4
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• pp.458-467
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• 2016

Cement-retained implant prosthesis has several advantages in the esthetic and occlusal aspects. However, the difficulty of the retrievability and the possibility of peri-implantitis induced by the cement excess would be a threatening factor to the implant prognosis. Peri-implantitis resulting from the remaining cement could occur later on to the patients with periodontitis history. Retention can be controlled by selecting the right cement type. Retention of the cement was the strongest in the resin cement, followed by resin modified glass ionomer cement, poIycarboxylate cement, zinc phosphate cement and glass ionomer cement. Retention of the provisional cement weakened after thermocycling. Other factors such as the abutment number, abutment alignment, height and taper of the abutment can also affect the total retention. To the success of the cement-retained prosthesis, it's important to select the right cement for the clinical purpose. The prosthesis should be fabricated in accordance with the biomechanical requirements. The prosthesis should be cemented with the techniques to reduce the excess cement as much as possible. In addition, the excess cement should be identified using the radiography and carefully removed.

• Journal of the korean academy of Pediatric Dentistry
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• v.34 no.2
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• pp.322-328
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• 2007

The first molar is important for mastication and also it plays roles to formation of vertical occlusion and growth of jaw bone after mixed dentition. Impaction of mandibular first molar can result in a short lower facial height, formation of a follicular cyst, pericoronal inflammation, resorption of the roots of neighboring teeth and malocclusion. The options of treatment plans are as follows; observation, surgical exposure, orthodontic traction, surgical relocation and extraction. Surgical exposure could be considered as a basic treatment plan. For surgical exposure it is important to maintain patent channel between the crown and the normal eruptive path into the oral cavity, many techniques including cementation of a celluloid crown, packing with zinc oxide-eugenol surgical pack are used. In these cases, we could observe spontaneous eruption of mandibular first molar using surgical exposure with or without removal of odontoma. Also we could obtain the main patency effectively and conveniently by using surgical pack and translucent retainer.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.4
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• pp.426-437
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• 2005

Statement of problem : Although zirconium oxide ceramics are more and more commonly used in restorative dentistry, for many clinical applications only limited data can be found in the literature. However it is quite clear that hydrofluoric acid etching is impossible with zirconia ceramics. Therefore, other bonding techniques are required in order to lute these materials adhesively. Purpose : The purpose or this study was to evaluate the effects of surface treatments on shear bond strengths between two resin cements and a zirconia ceramic. Materials and methods : Experimental industrially manufactured yttrium-oxide-partially-stabilized zirconia ceramic discs (Adens, Korea) were used for this study. The ceramic specimens divided into five experimental groups and a control group (as received). Five surface treatments were studied 1) sandblasting with 110$\mu$m $Al_2O_3$ at 3 bars pressure 13 seconds at a distance of 10 mm, 2) flame-treated with the Silano-Pen for 5 $s/cm^3$, 3) grinding with a diamond bur. 4) sandblasting + Silano-Pen treatment, 5) diamond bur preparation + Silano-Pen treatment. Acrylic plastic tube (5 mm in height and 3 mm in diameter) were filled with composite to fabricate composite cylinders The composite cylinders were bonded to the ceramic specimens with either Superbond C&B or Panavia F resin luting agents. All cemented specimens were tested under shear loading until fracture on universal testing machine at a crosshead speed 1mm/min; the maximum load at fracture was recorded. Sheat bond strength data were analyzed with oneway analysis of variance and Tukey HSD tests (P<.05). Treated ceramic surfaces and fracture surfaces after shear testing were examined morphologically using scanning electron microscope. Results: Ceramic surface treatment with Silano-Pen after sandblasting improved the bond strength of Superbond C&B resin cement. Supevbond C& B resin cement at Silano-Pen aiker sandblasting($27.4{\pm}3.8MPa$) showed statistically higher shear bond strength than the others. Conclusion: Within the limitation of this study, Superbond C& &B resin cement are suitable for cementation of zirconia ceramics and flame-treated with the Silano-Pen after sandblasting is required to enhance the bond strength.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.835-841
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• 1995

The deposition properties of Si$_3$N$_4$ deposited by low pressure chemical vapor deposition were studied to evaluate Si$_3$N$_4$as part of multi-layer coatings for anti-oxidation and anti-wear coating of graphite in the propellant-burning environment. Si$_3$N$_4$was deposited on the pack-SiC coated graphite and the tendencies of deposition rate and surface morphology changes with temperatures and reaction gas ratios were investigated. In low deposition temperatures the deposition rate increased tilth increasing temperature but in high temperatures the deposition rate decreased with increasing temperature. The grain size of Si$_3$N$_4$decreased with increasing temperature. In condition that the range of reaction gas ratios is 20$\leq$NH$_3$/SiH$_4$$\leq$40, the deposition rate and surface morphology did not change. The Si$_3$N$_4$deposited at 800~130$0^{\circ}C$ was amorphous, and by post-annealing at 130$0^{\circ}C$ in a $N_2$ambient, the Si$_3$N$_4$crystalized.

• Resources Recycling
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• v.13 no.1
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• pp.14-21
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• 2004

Spent catalysts containing platinum were generated in petroleum refinery and other chemical industries. The reclamation of platinum metals from such wastes has long been attempted in view of their rare, expensive and indispensable nature. In this study, the recovery of platinum from petroleum catalysts was attempted by a method consisting mainly of dissolving alumina carrier with sulfuric acid thereby concentrating insoluble platinum. Also, platinum dissolved partially in sulfuric acid was recovered by a cementation method using aluminum metal as a reductive agent. The effect of temperature, time, concentration of sulfuric acid, and pulp density on the dissolution of carrier was investigated. When the carrier of platinum catalyst was $\Upsilon-Al_2$O$_3$ about 95% alumina was dissolved in 6.0 M sulfuric acid at $100^{\circ}C$ for 2 hours. When the carrier was the mixture of $\Upsilon-Al_2$$O_3$ and $\alpha$-$Al_2$$O_3$ about 92% was dissolved after 4 hours. As a result, more than 99% of platinum could be recovered by this method and aluminum sulfate was also obtained as byproduct.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.5
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• pp.489-500
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• 2004

Statement of problem: The use of zirconia prostheses fabricated with CAD/CAM system is on an increasing trend in dentistry. However, evaluation of the fit related to internal relief and marginal reproducibility of zirconia has not been reported. Purpose : This study was to evaluate the fit related to internal relief and marginal reproducibility of zirconia core fabricated with CAD/CAM system. Materials and methods: The evaluation was based on 30 zirconia cores and 5 IPS-Empress2 cores. Zirconia cores were fabricated in different conditions of internal relief(0, 10, 20, 30, 40 and $50{\mu}m$), and IPS-Empress2 cores were fabricated in accordance with the manufacturer's instructions. Before cementation, the marginal discrepancies or cores were measured on metal die. And then, each core was cemented to stone die, embedded in an acrylic resin and sectioned in two planes(mesiodistally and labiopalatally). The internal gaps were measured at the margin and axial surface. Measurements for the marginal discrepancies, the internal marginal gaps and the internal axial gaps were performed under a measuring microscope(Compact measuring microscope STM5; Olympus, Japan) at a magnification of ${\times}100$. In addition, the marginal conagurations of metal die, zirconia core and IPS-Empress2 core were examined with SEM(S-2700, Hitachi, Japan). Results : Within the limits of this study the results were as follows. 1. Compared with IPS-Empress2 cores, the marginal discrepancies of zirconia cores had no significant differences. the internal marginal gaps were statistically smaller and the internal axial gaps were statistically larger in each condition of internal relief. 2. The marginal discrepancies and the internal marginal gaps of zirconia cores had no significant differences related to the conditions of internal relief(P>0.05). 3. The internal axial gaps of zirconia cores with $0{\sim}20{\mu}$m for internal relief were significantly larger than that with $50{\mu}m$ (P<(0.0001). 4. SEM micrographs showed favorable marginal reproducibility of zirconia core and smooth texture on the milling surface. Conclusion: The marginal discrepancy and the internal gaps of zirconia core were clinically acceptable and the milling surface was showed smooth texture. For fabrication of the durable esthetic restoration, further investigations on complex design of core, milling accuracy, compatability of enamel porcelain and porcelain firing seems to be needed.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.5
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• pp.501-513
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• 2004

Purpose : The purpose of this study was to evaluate the effects of etching time on shear bond strength of four resin cements to IPS Empress 2 ceramic. Material and Methods: Forty rectangular shape ceramic specimens ($10{\times}15{\times}3.5mm$ size) were used for this study. The ceramic specimens divided into four groups and were etched with 10% hydrofluoric acid for 0, 10, 30, 60, 180, 300, 420, 600, and 900 seconds respectively. Etched surfaces of ceramic specimens were coated with ceramic adhesive system and bonded with four resin cement (Variolink II, Panavia F, Panavia 21, Super-Bond C&B) using acrylic glass tube. All cemented specimens were tested under shear loading untill fracture on universal testing machine at a crosshead speed 1mm/min: the maximum load at fracture (kg) was recored. Shear bond strengh data were analyzed with oneway analysis of variance and Tukey HSD tests (p<.05). Etched ceramic surfaces (0-, 60-, 300-, and 600-seconds etching period) and fracture surfaces after shear testing were examined mophologically using scanning electron microscopy. Results : Ceramic surface treatment with 10% hydrofluoric acid improved the bond strength of three resin cement except for Super-Bond C&B cement. Variolink II (41.0$\pm$2.4 MPa) resin cement at 300-seconds etching time showed statistically higher shear bond strength than the other resin cements (Panavia F: 28.3$\pm$2.3 MPa, Panavia 21: 21.5$\pm$2.2 MPa, Super-Bond C&B: 16.7$\pm$1.6 MPa). Ceramic surface etched with 10% hydrofluoric acid for 300 seconds showed more retentive surface texture. Conclusion: Within the limitation of this study, Variolink II resin cement are suitable for cementation of Empress 2 all-ceramic restorations and etching with 10% hydrofluoric acid for 180 to 300 seconds is required to enhance the bond strength.

• Economic and Environmental Geology
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• v.43 no.2
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• pp.85-100
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• 2010

Devonian Cairn Formation is one of the important hydrocarbon reservoirs in Alberta, Canada. However, the Cairn Formation, outcropped in the study area, is not prospective reservoir with poor porosity and permeability by some late diagenetic processes. In this study, geochemical characteristics of the Cairn Formation were studied to use these preliminary results for advanced geological and geophysical petroleum explorations in the near future. Rock-Eval pyrolysis showed that total organic carbon content is less than 0.3 wt.%, indicating a minor amount of bitumen and/or other hydrocarbons. The carbonates in the Cairn Formation are mainly composed of subhedral and anhedral dolomites. Pore sizes in the carbonate are various, ranging from nanometer to micrometer. Clastic sediments increase in the upper and lower parts of the Cairn Formation, probably due to changing its depositional conditions. The Cairn Formation can also be divided into several intervals based on Ca/Mg ratio in dolomite and degree of amount of calcite. These could be formed by different sedimentary environment, degree of cementation and recrystallization, different saline/fresh water, etc.

• Journal of the Korean Geotechnical Society
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• v.27 no.12
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• pp.17-25
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• 2011

A fabric of soil media may change due to certain factors such as dissolution of soluble particles, desiccation, and cementation. The fabric changes affect the mechanical behavior of soils. The purpose of this study is to investigate the effects of geo-material dissolution on shear strength. Experiments and numerical simulations are carried out by using a conventional direct shear and the discrete element method. The dissolution specimens are prepared with different volumetric salt fraction in sand soils. The dissolution of the specimens is implemented by saturating the salt-sand mixtures at different confining stresses in the experimental study or reducing the sizes of soluble particles in the numerical simulations. Experimental results show that the angle of shearing resistance decreases with the increase in the soluble particle content and the shearing behavior changes from dilative to contractive behavior. The numerical simulations exhibit that macro-behavior matches well with the experimental results. From the microscopic point of view, the particle dissolution produces a new fabric with the increase of local void, the reduction of contact number, the increase of shear contact forces, and the anisotropy of contact force chains compared with the initial fabric. The shearing behavior of the mixture after the particle dissolution is attributed to the above micro-behavior changes. This study demonstrates that the reduction of shearing resistance of geo-material dissolution should be considered during the design and construction of the foundation and earth-structures.

• Journal of the Korean GEO-environmental Society
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• v.17 no.12
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• pp.17-26
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• 2016

The experimental investigation aims at developing controlled low strength materials (CLSM) using a self-cementitious fly ash (FA) as a binder and a bottom ash (BA) as a aggregate. The fly ash and bottom ash used in this study were obtained from a circulating fluidized bed combustion boiler (CFBC) which produces relatively high CaO containing fly ash. To find the optimum mixing condition satisfying flow consistency and unconfined compression strength (UCS), the CLSM specimens were prepared under various mixing conditions, including two types of aggregate and different weight fractions between fly ash and aggregate. Additionally, the prepared specimens were evaluated using a scanning electron microscope (SEM) and X-ray diffraction (XRD). The results of this study demonstrate that the water content satisfying flow consistency ranges from 42% to 85% and the flowability is improved with increasing the fraction of aggregate in whole mixture. The USC ranges from 0.3 MPa to 1.9 MPa. The results of UCS increases with increasing the fraction of aggregate in FA-sand mixtures, but decreases with increasing the fraction of aggregate in FA-BA mixtures. SEM images and XRD patterns reveal that the occurrence of both geopolymerization and hydration. The results of this study demonstrate that CFBC fly ash could be used as an alternative binder of CLSM mixtures.