• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.26 no.2
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• pp.133-145
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• 1996

Aspirating or swallowing foreign bodies is a common occurrence. If they are wholly or partly radiopaque, their localization in and progress through the gastrointestinal tract can be more effective. Of the dental origin foreign materials swallowed, the most common things are fragments of anterior maxillary partial denture. But the radiopacity of denture base resins is not sufficient to determine the location of the objects. The purpose of this study was to develop a radiopaque dental acrylic resin, which has clinically detectible radiopacity with minimal change of mechanical properties and color. The radiopacity, color change(CIE 6..E) and microhardness of acrylic resins were determined after mixing barium sulfate or iodide compound. Thermocycling course was conducted to determine the change of characteristic of resins after using for a long time in the mouth. Five or ten percent of barium sulfate to total weight of cured material was mixed with heat curing dental acrylic resin or chemically curing orthodontic resin. In the case of iodide compound, the mixing ratio was two or three percent. After mixing the high radiopaque materials, resin was cured to 20×20×2 mm plate, polished with #600 sand paper and finally polished with Microcloth(Buehler). The specimens were thermocycled in 5 and 55 t distilled water for 2,000 times, and the measurement of radiopacity, color and Vickers hardness was repeated every 500 times thcrmocycling. The radiopacity of specimens on the X -ray films was measured with densitometer(X-rite). The color change was detennined with differential colorimeter(Model TC-6FX, Tokyo Denshoku), and the Vickers hardness number was measured with microhardness tester(Mitsuzawa). The following results were obtained : 1. All the three variables, the kinds of acrylic resins, the mixing or the kinds of high radiopaque materials and thermocycling, had combined effect on the radiopacity of the dental acrylic resins(p<0.0l). 2. The two variables, the mixing or the kinds of high radiopaque materials and thermocycling, influenced on the radiopacity of the dental acrylic resins(p<0.01). But the kinds of acrylic resins did not influence on the color change of mixed dental acrylic resins(p>0.05). 3. Each of the three variables, the kinds of acrylic resins, the mixing or the kinds of high radiopaque materials and thermocycling, influenced on the radiopacity of dental acrylic resins(p<0.0l). 4. The high radiopaque materials used in this study did not yield clinically usable radiopacity, and the color change was great after mixing those materials.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.3
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• pp.284-294
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• 2006

Statement of problem. Proliferation of Candida albicans is primarily within the plaque on the fitting surface of the denture rather than on the inflamed mucosa. Consequently, the treatment of the denture is equally important as treatment of the tissue. Cleansing and disinfection should be efficiently carried-out as the organisms can penetrate into the voids of the acrylic resin and grow in them, from which they can continue to infect and reinfect bearing tissues. Purpose. The purpose of this study was to evaluate the applicability of photocatalytic reaction to eliminate Candida albicans from acrylic resin denture base, and to investigate the anti-fungal effect with various UVA illumination time. Materials and Methods. The specimens were cured by the conventional method following the manufacturer's instruction using thermal polymerized denture base resin (Vertex RS: Dentimex, Netherlands). $TiO_2$ photocatalyst sol(LT), which is able to be coated at normal temperature, was made from the Ti-alkoxide progenitor. The XRD patterns, TEM images and nitrogen absorption ability of the $TiO_2$ photocatalyst sol(LT) were compared with the commercial $TiO_2$ photocatalyst P-25. The experimental specimens were coated with the mixture of the $TiO_2$ photocatalyst sol(LT) and binder material (silane) using dip-coater, and uncoated resin plates were used as the control group. Crystallinity of $TiO_2$ of the specimen was tested by the XRD. Size, shape and chemical compositions were also analyzed using the FE-SEM/ EDS. The angle and methylene blue degradation efsciency were measured for evaluating the photocatalytic activity of the $TiO_2$ film. Finally, the antifungal activity of the specimen was tested. Candida albicans KCTC 7629(1 ml, initial concentration $10^5$ cells/ ml) were applied to the experiment and control group specimens and subsequently two UVA light source with 10W, 353 nm peak emission were illuminated to the specimens from 15cm above. The extracted $2{\mu}l$ of sample was plated on nutrient agar plate ($Bacto^{TM}$ Brain Heart Infusion; BD, USA) with 10 minute intervals for 120 minute, respectively. It was incubated for 24 hours at $37^{\circ}C$ and the colony forming units (CFUs) were then counted. Results. Compared the characteristics of LT photocatalyst with commercial P-25 photocatalyst, LT were shown higher activity than P-25. The LT coated experimental specimen surface had anatase crystal form, less than 20 nm of particle size and wide specific surface area. To evaluate the photocatalytic activity of specimens, methylene blue degradation reaction were used and about 5% of degradation rate were measured after 2 hours. The average contact angle was less than $20^{\circ}$ indicating that the LT photocatalyst had hydrophilicity. In the antifungal activity test for Candida albicans, 0% survival rate were measured within 30 minute after irradiation of UVA light. Conclusion. From the results reported above, it is concluded that the UVA-LT photocatalytic reaction have an antifungal effect on the denture surface Candida albicans, and so that could be applicable to the clinical use as a cleaning method.

• Restorative Dentistry and Endodontics
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• v.34 no.2
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• pp.145-153
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• 2009

The purpose of this study was to evaluate the effect of instrument compliance on the polymerization shrinkage stress measurements of dental composites. The contraction strain and stress of composites during light curing were measured by a custom made stress-strain analyzer, which consisted of a displacement sensor, a cantilever load cell and a negative feedback mechanism. The instrument can measure the polymerization stress by two modes: with compliance mode in which the instrument compliance is allowed, or without compliance mode in which the instrument compliance is not allowed. A flowable (Filtek Flow: FF) and two universal hybrid (Z100: Z1 and Z250: Z2) composites were studied. A silane treated metal rod with a diameter of 3.0 mm was fixed at free end of the load cell, and other metal rod was fixed on the base plate. Composite of 1.0 mm thickness was placed between the two rods and light cured. The axial shrinkage strain and stress of the composite were recorded for 10 minutes during polymerization. and the tensile modulus of the materials was also determined with the instrument. The statistical analysis was conducted by ANOVA. paired t-test and Tukey's test (${\alpha}<0.05$). There were significant differences between the two measurement modes and among materials. With compliance mode, the contraction stress of FF was the highest: 3.11 (0.13). followed by Z1: 2.91 (0.10) and Z2: 1.94 (0.09) MPa. When the instrument compliance is not allowed, the contraction stress of Z1 was the highest: 17.08 (0.89), followed by FF: 10.11 (0.29) and Z2: 9.46 (1.63) MPa. The tensile modulus for Z1, Z2 and FF was 2.31 (0.18), 2.05 (0.20), 1.41 (0.11) GPa, respectively. With compliance mode. the measured stress correlated with the axial shrinkage strain of composite: while without compliance the elastic modulus of materials played a significant role in the stress measurement.

• The Journal of Korean Academy of Prosthodontics
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• v.58 no.3
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• pp.207-216
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• 2020

Purpose: To compare the polishing characteristics and their influence on Candida albicans adhesion to the recently introduced polyetherketoneketone (PEKK) and the conventional polymethylmethacrylate (PMMA) denture resin material. Materials and methods: Specimens from PEKK (Group E) and PMMA (Group M) were made in dimensions of 8 mm in diameter and 2 mm in thickness. The specimens were further divided into sub-groups according to the extent of polishing (ER, MR: rough; EP, MP: polished, N = 12 each). The specimens were polished using polishing machine and SiC foil. ER and MR group specimens were polished with 600 grit SiC foil only. EP and MP groups were further polished with 800, 1,000, 1,200 grit SiC foils sequentially. To measure the surface roughness values (Sa) of specimens, atomic force microscope (AFM) was used and scanning electron microscope (SEM) observation under 1,000, and 20,000 magnifications was performed to investigate surface topography. The polished specimens were soaked in C. albicans suspension for 2 hours with shaking to promote adhesion. The attached C. albicans were detached from the surface with 10 times of pipetting. The suspension of detached C. albicans was performed by serial dilution to 10³ times, and the diluted suspensions were inoculated on Sabouraud dextrose agar plates using spread plate method. After incubating the plate for 48 hours, colony forming unit (CFU)/plate of C. albicans was counted. Statistical analysis was performed using one-way ANOVA and Tukey HSD test to confirm significant difference between the groups (α=.05). Results: Average Sa value was significantly higher in MR group compared to other groups (P<.05), meaning that additional polishing steps reduced surface roughness effectively only in the PMMA specimens. There was no significant difference in Sa values between MP and EP groups. In SEM images, PEKK specimens showed numerous spikes of abraded material protruding from the surface and this phenomenon was more significant in EP group. The mean CFU/plate value was the highest in EP group and this was significant when it was compared to MP group (P<.05) which was the lowest. Conclusion: Polishing PEKK using serial SiC abrasive foil may result in higher adhesion of C. albicans. In clinic, this should be considered carefully.

• Journal of the Korean Society for Railway
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• v.19 no.4
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• pp.417-426
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• 2016

In this study, the optimal welding condition of an extruded AZ61 magnesium alloy plate was investigated through evaluation of the mechanical properties and microstructure in the friction stir welding zones. The friction stir welding conditions considered in this study were the tool rotation speeds of 400, 600, and 800rpm and the welding speeds of 200, 300, and 400mm/min. To evaluate the welding strength, tensile and hardness tests were carried out. Microstructures of the welded regions were examined using optical microscopes. Under a tool rotation speed of 800rpm and welding speed of 200mm/min, the joint showed the best joining properties. The UTS, yield strength, and elongation of the welded region showed values of 79.0%, 65.4%, and 30.1%, respectively, of those of the base metal.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.7
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• pp.52-59
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• 2020

Automatic tool changers (ATCs) can be divided into drum and chain types. Drum-type ATCs contain a magazine, where the tools are mounted, and a cam gearbox, which swaps the tools via roller gear and grooved plate cams. Drum-type ATCs are advantageous in that the operating time for the tool magazine is more rapid than that of chain-type ATCs and the length of the unit is shorter. Thus, drum-type ATCs can be fabricated into various shapes and forms depending on the number of tools and the magazine size in accordance with machining center requirements and consumer demand. In particular, the price competitiveness of a machining center with a drum-type ATC is higher, while drum-type ATCs are more rigid with fewer parts, possibly reducing the need for regular servicing. This study aims to verify the structural stability and design validity of the magazine base, which is the main structure of a drum-type ATC, using finite element analysis. This study kinematically verifies the specifications of the selected drive motor and reducer and assessed the design of the cam gearbox. It also conducts a structural analysis of the roller camp, which is the core component of the cam gearbox, based on the results of the kinetodynamic analysis, thus validating the structural design.

• The Journal of Advanced Prosthodontics
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• v.6 no.3
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• pp.207-214
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• 2014

PURPOSE. This study characterized the synthesis of a modified PMMA (Polymethyl methacrylate) denture acrylic loading platinum nanoparticles (PtN) and assessed its bacterial inhibitory efficacy to produce novel antimicrobial denture base material. MATERIALS AND METHODS. Polymerized PMMA denture acrylic disc ($20mm{\times}2mm$) specimens containing 0 (control), 10, 50, 100 and 200 mg/L of PtN were fabricated respectively. The obtained platinum-PMMA nanocomposite (PtNC) was characterized by TEM (transmission electron microscopy), SEM/EDX (scanning electron microscope/energy dispersive X-ray spectroscopy), thermogravimetric and atomic absorption spectrophotometer analysis. In antimicrobial assay, specimens were placed on the cell culture plate, and $100{\mu}L$ of microbial suspensions of S. mutans (Streptococcus mutans) and S. sobrinus (Streptococcus sobrinus) were inoculated then incubated at $37^{\circ}C$ for 24 hours. The bacterial attachment was tested by FACS (fluorescence-activated cell sorting) analysis after staining with fluorescent probe. RESULTS. PtN were successfully loaded and uniformly immobilized into PMMA denture acrylic with a proper thermal stability and similar surface morphology as compared to control. PtNC expressed significant bacterial anti-adherent effect rather than bactericidal effect above 50 mg/L PtN loaded when compared to pristine PMMA (P=.01) with no or extremely small amounts of Pt ion eluted. CONCLUSION. This is the first report on the synthesis and its antibacterial activity of Pt-PMMA nanocomposite. PMMA denture acrylic loading PtN could be a possible intrinsic antimicrobial denture material with proper mechanical characteristics, meeting those specified for denture bases. For clinical application, future studies including biocompatibility, color stability and warranting the long-term effect were still required.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.2
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• pp.94-102
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• 2009

Conceptual design of scroll expander and scroll compressor for 10kW-class Stirling engine utilizing solar energy as heat source has been carried out to estimate the applicability of scroll mechanism for Stirling cycle. CO2 was chosen as working fluid, since it has lower expansion index and higher density among probably usable gases. Gas temperature at the expander inlet was set at $700^{\circ}C$, and that at the compressor inlet was at $40^{\circ}C$. System efficiency reached maximum at the pressure ratio of about 2.5, and the peak efficiency increased with increasing high side pressure. Due to safety concern, the pressure condition of 6 MPa/2.5 MPa was chosen as design condition. Orbiting scroll members for the expander and compressor were designed to have double-sided structure in order to reduce the overall scroll size and to cancel out the axial gas forces acting on the orbiting scroll base plate. By parametric study on the scroll profile, smaller possible size for the scroll members was obtained. With the shaft speed of 3600rpm, the shaft output of the designed scroll expander was calculated to be 45.4kW, while input power for the scroll compressor was 34.5kW, yielding 10.9kW for the output power of the Stirling engine. System efficiency was estimated to be about 7.3%, and overall efficiencies of the scroll expander and compressor were around 84.1% and 88.3%, respectively.

• Journal of Institute of Convergence Technology
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• v.8 no.1
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• pp.21-25
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• 2018

We developed nano-porous $TiO_2-SiO_2$ composites (commercial name : PTI, porous titania insulator) with low thermal conductivity as thermal insulating material as well as function of photocatalyst. The objectives of this paper are, firstly, to evaluate of the thermal conductivity of the PTI powder in the temperature range from -160 to $250^{\circ}C$, secondly to evaluate of thermal conductivities of insulation materials that is applied PTI powder. The structure of the PTI powder that has the pores size of 20-30 nm and the particle diameter of 2-10 nm. The PTI had a high surface area of $400m^2/g$ and a mean pore size of $45{\AA}$, which was fairly uniform. The thermal conductivity was measured by GHP(guarded hot plate) method and HFM(heat flux method). The PTI structure is a three-dimensional network nano-structures composed by a pearl-necklace that involved a precious stone in the center of the necklace. The thermal conductivities of PTI-PX powder by the GHP and HFM were 0.0366 W/m.K, 0.0314 W/m.K at $20^{\circ}C$, respectively. This is similar to values that are proportional to the square of the absolute temperature of the thermal conductivity of static air. The thermal conductivities of insulating sheets coated with PTI powder were similar results with that of the PTI powder.

• Journal of Korean Dental Science
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• v.16 no.1
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• pp.23-34
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• 2023

Purpose: This study aims to investigate the force delivery profile of thermoformed aligners (TFA) compared with direct-printed aligners (DPA) and to explore the effect of different activation amounts on forces and moments of respective groups. A secondary objective is to observe the amount of stress relaxation that occurs over the 7~14 days when aligners are maintained in a simulated intraoral environment. Materials and Methods: An in vitro setup was created to quantify forces and moments. It consisted of a three dimensional-printed base plate and segmented maxillary teeth, placed in a semi-enclosed chamber to maintain a temperature of 37℃. Ninety clear aligners were divided into nine groups of ten aligners each based on material types (Zendura, ATMOS, TC-85) and activation amounts. Aligners were created with 0.00, 0.25- and 0.50-mm activations for lingual bodily movement of the upper left central incisor and kept on models in the "stressed" position in a 37℃ water bath. Three force components acting on the upper left lateral incisor, upper left central incisor, and upper right central incisor were measured for each time point, beginning from the initial baseline measurement, 8 hours, 16 hours, 24 hours, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, and lastly, 14 days. Result: TC-85 aligners in every activation group showed less force on teeth than Zendura and ATMOS. Significant force levels from 0.0 mm activation were present and stayed consistent over the course of 14 days. Comparisons made for baseline measurements to 7-days and 14-days showed statistically significant change from the baseline force level. Conclusion: TC-85 aligners demonstrated lower, more consistent forces with fewer side effects. Aligners can generate forces even when no activation is programmed. No major decreases in force levels over time were observed; the intra-oral clinical simulated environment and length of observation time could contribute to this.