• The Journal of Korean Academy of Prosthodontics
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• v.43 no.5
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• pp.587-598
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• 2005

Statement of problem: Ceramic restorations should be made of porcelain layers of different opacity, shade, and thickness in order to provide a natural appearance. Lithium disilicate glass-ceramic system has superior color reproducibility, because it uses the ceramic ingot which is similar to teeth shade and uses the staining technique and layering technique. However, staining technique has a fault of discoloration. Also, porcelain is divided core and dentin layer, it is not enough to study about the influence of porcelain layer thickness and shade on the shade of ceramic restorations. Purpose: The purpose of this study was to evaluate the influence of porcelain layer thickness and color on the final shade of ceramic restorations. Materials and method: The CIE $L^*a^*b^*$(CIELAB) values of 72 assembled specimens, each consisting of 3 discs (enamel porcelain 0.2 mm/dentin porcelain -1.2, 0.9, 0.7, 0.5 or 0.3 mm/ceramic core -0.3, 0.5, 0.7, 0.9 or 1.2 mm, diameter is 1.0 mm) were evaluated with a spectrophotometer (Model Chromaview 300, Spectron Tech Co, Korea) for the shade A1, A2, A3 and A4. Distilled water (refractive index: 1.7) was used to attain optical contact between the layers. White, white gray, and white brown backgrounds were used to assess the influence of the background on the final shade. And the mean color difference value$({\Delta}E)$ was calculated. Results and conclusion: The results obtained from this study were as follows. 1. There was a significant correlation between the thickness ratio of the ceramic core/dentin porcelain system and $L^*,\;a^*\;and\;b^*$ values when the total thickness of specimen combination was smaller than 1.4 mm(P<0.05). 2. The specimen which the ceramic core thickness was more than 0.7 mm had the best masking effect against background colors. 3. The mean color difference value$({\Delta}E)$ is smaller than 2 $({\Delta}E<2)$ when the ceramic core thickness was larger than 0.7 mm and the total thickness of specimen was more than 1.4 mm.

• 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.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.5
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• pp.611-620
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• 2007

Statement of problem: Second-generation indirect composite resins have been improved flexural strength, compressive strength, hydrolytic degradation resistance, wear resistance compared to first-generation indirect composite resins, but there are still some problems as hydrolysis and low wear resistance. Some manufacturers claim that wear resistance of their materials has been improved, but little independent study has been published on wear properties of these materials and the properties specified in the advertising materials are largely derived from in-house or contracted testing. Purpose: This study was to evaluate the wear of indirect composite resins (SR Adore, Sinfony, Tescera ATL) and gold alloy against the human enamel. Material and method: Extracted human incisors and premolars were sectioned to $2{\times}2{\times}2mm$ cube and embedded in the clear resin and formed conical shaped antagonist to fit the jig of pin-on-disk tribometer. Total 20 antagonists were stored in distilled water. Five disk samples, 24mm in diameter and 1.5mm thick, were made for each of three groups of indirect composite resins and gold alloy group, and polished to #2,000 SiC paper on auto-polishing machine. Disk specimens were tested for wear against enamel antagonists. Wear test were conducted in distilled water using a pin-on-disk tribometer under condition (sliding speed 200rpm contact load 24N, sliding distance 160m). The wear of the enamel was determined by weighing the enamel antagonist before and after test, and the weight was converted to volumes by average density. The wear tracks were analyzed by scanning electron microscopy and surface profilometer to elucidate the wear mechanisms. Statistical analysis of the enamel wear volume, wear track depth and wear tract width of disk specimens were accomplished with one-way ANOVA and the means were compared for significant differences with Scheffe's test. Results: 1. The enamel wear was most in gold alloy, but there were no statistically significant differences among all the groups (P>.05). 2. In indirect composite resin groups, the group to make the most shallow depth of wear tract was Sinfony, followed by Tescera ATL, SR Adoro (P<.05). Gold alloy was shallower than Sinfony, but there was no statistically significant difference between Sinfony and gold alloy (P>.05). 3. The width of wear tract of SR Adore was larger than the other groups (P<.05), and there were no statistically significant differences among the other groups (P>.05). 4. SEM analysis revealed that Sinfony and gold alloy showed less wear scars after test, Tescera ATL showed more wear scars and SR Adore showed the most. Conclusion: Within the limits of this study, Sinfony and gold alloy showed the least wear rates and showed similar wear patterns.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.2
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• pp.153-158
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• 2004

Preformed stainless steel crown is an useful restorative material for the treatment of badly broken down primary teeth. However iatrogenic damage to adjacent teeth might occur during the process of tooth reduction. Such damages might lead to plaque accumulation and increase the risks of caries initiation. Especially the damage can make a problem in the first permanent molar. Purpose of this study was to investigate an iatrogenic damage to the first permanent molar during preparation of second primary molar for preformed stainless steel crown. Twelve children restored with preformed stainless steel crown to second primary molar were selected. Contact areas were separated with separation elastics, and tooth surfaces were cleaned. After taking negative impression using vinylpolysiloxane impression material, the specimens were examined by scanning electron microscope for the detection of iatrogenic damage. The prevalence of iatrogenic damage was 66.7% and variable appearances and So we can suggest that when preparing teeth for preformed stainless steel crown, we should be careful about adjacent teeth not to make an iatrogenic damage.

• Journal of the Korea Society for Simulation
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• v.20 no.1
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• pp.79-85
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• 2011

The problem of evacuating pedestrians from a room or channel under panic conditions is of obvious importance in daily life. In recent years, several computer models have been developed to simulate pedestrian dynamics. Understanding evacuation dynamics can allow for the design of more comfortable and safe pedestrian facilities. However, these models do not take into account the type and state of mind of pedestrians. They deal with pedestrians as particles and the state of mind as a social force, which is represented by conservative and long-range interactions between individuals. In this study, I used the lattice model proposed in my previous study to explore the evacuation behavior of pedestrians with morality. In this model, three types of pedestrians are considered: adults, children, and injured people. Collisions between adults and children result in injured people. When the number of injured people continuously in contact with each other reaches a given value k, the injured people are removed from the lattice space. This situation is the same as that in which pedestrians start stepping over injured people. This behavior was interpreted as the morality of pedestrians. Simulations showed that the evacuation showed down and eventually became jammed owing to the injured people acting as "obstacles" in relation to the morality k.

• The Journal of Advanced Prosthodontics
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• v.1 no.2
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• pp.107-112
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• 2009

STATEMENT OF PROBLEM. Macroscopic and especially microscopic properties of implant surfaces play a major role in the osseous healing of dental implants. Dental implants with modified surfaces have shown stronger osseointegration than implants which are only turned (machined). Advanced surface modification techniques such as anodic oxidation and Ca-P application have been developed to achieve faster and stronger bonding between the host bone and the implant. PURPOSE. The purpose of this study was to investigate the effect of surface treatment of titanium dental implant on implant stability after insertion using the rabbit tibia model. MATERIAL AND METHODS. Three test groups were prepared: sandblasted, large-grit and acid-etched (SLA) implants, anodic oxidized implants, and anodized implants with Ca-P immersion. The turned implants served as control. Twenty rabbits received 80 implants in the tibia. Resonance frequencies were measured at the time of implant insertion, 2 weeks and 4 weeks of healing. Removal torque values (RTV) were measured 2 and 4 weeks after insertion. RESULTS. The implant stability quotient (ISQ) values of implants for resonance frequency analysis (RFA) increased significantly (P <. 05) during 2 weeks of healing period although there were no significant differences among the test and control groups (P >. 05). The test and control implants also showed significantly higher ISQ values during 4 weeks of healing period (P < .05). No significant differences, however, were found among all the groups. All the groups showed no significant differences in ISQ values between 2 and 4 weeks after implant insertion (P >. 05). The SLA, anodized and Ca-P immersed implants showed higher RTVs at 2 and 4 weeks of healing than the machined one (P < .05). However, there was no significant difference among the experimental groups. CONCLUSION. The surface-modified implants appear to provide superior implant stability to the turned one. Under the limitation of this study, however, we suggest that neither anodic oxidation nor Ca-P immersion techniques have any advantage over the conventional SLA technique with respect to implant stability.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.23-32
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• 2017

The joints between precast PSC slabs of the intermediate road slab in double deck tunnel are inevitably generated in the road traffic vehicle traveling direction. Therefore, it is important to make the behavior of parts on the joint in one piece. The imtermediate road slab system of double deck tunnel in great depth proposed in this study will be constructed with precast PSC slab in order to minimize the construction period. And the joint connection between the precast slab has been developed in two methods: the 'Transverse tendon reinforcement method' and 'High strength bolts connection method'. Also, the experiments were performed for the full scale model in order to evaluate the performance of the intermediate road deck slab with two type joints systems, the structural stability was verified through the F.E.M analsysis. The results of static loading test and F.E.M analysis investigated a very stable behavior of intermediate road deck slab in double deck tunnel applying the joint methods developed in this study, in the cracks and deflections to satisfy the design standards of Highway Roads Bridges (2011), it was determined that there is no problem even servicebility.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.1023-1026
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• 2006

There are some cases in trouble with monitoring emergency patient by existing electrode sensor in measuring instrument in home and hospital etc. And there are problem to measure because of coming down electrode in emergency car or vessel of shaking and fat, humidity of patient. In this study, it has designed band-type for patient to put on the breast easily and go around anywhere freely putting band electrode on his body. Gold has used as electrode material in this electrocardiogram because of its excellent electronic resistance peculiarity and no trouble with skin. And it is able to monitor multi-body-signal by additional design of periphery temperature. There are good results of body signal transmission in the breast or the rib, and get a little body signal in abdomen. We get a result it is better case of gold than usual electrode on signal detection, and know usual electrode was disposable, but we have more correct result from gold electrode sensor, being semi-permanent ana. great contact ability even if movement.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.1
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• pp.15-21
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• 2004

It is possible to detect flaws in pipelines without interruption using all EMAT transducer because it is a non-contact transducer which can transmit ultrasonic waves into specimens without couplant. And it ran easily generate guided waves desired in each specific problem by altering the design of coil and magnet. In the present work, EMAT systems have been fabricated to generate surface waves, and selectively the plate wave of $A_1\;or\;S_1$ mode. The surface wave of 1.5MHz showed a good signal-to-noise ratio without distortion in its propagation along a pipeline, while the $S_1$ mode of 800kHz and the $A_1$ mode of 940kHz were distorted according to their dispersive properties. The wider the excitation pulse becomes, the better the mode selectivity of the plate waves becomes. A pipe of 256mm inner diameter and 5.5m thickness with 5 flaws was used for comparing the flaw detectability among the modes under consideration.

• Journal of the Korean Society for Computer Game
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• v.31 no.4
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• pp.157-166
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• 2018

Communication between customers and service providers is an important issue at sites where various businesses and transactions take place. In particular, the ability to solve problems quickly and accurately when a problem arises and when an inquiry is received is directly linked to trust in the site. In this paper, we propose a method of handling complaints and inquiries of site users by using chatbot technology on talent market platform site. First, we implemented chatbot that can communicate with the inquirers in real time, so that users can use the site usage and word search functions. For various errors and problems of the site which can not be defined by a few words or sentences, I have specified an error code and database it. Users of the site were able to contact chatbot with the error code that was output when an error occurred and get the corresponding response in real time. The chatbot implemented in this study provided a satisfactory experience because that was able to provide quick and accurate answers to users who experienced errors or inquiries when using the site. This will have a positive impact on the credibility and favorability of the site over the long term, and will help reduce manpower and time costs for error inquiries.