• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.1
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• pp.15-18
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• 2003

High purity single crystalline calcium fluoride ($CaF_2$) has excellent optical transmission characteristics down to deep UV and is therefore selected as the main optical material for the next generation of lithography apparatus operating at wavelength of 157 nm. The growth of large sized $CaF_2$ single crystals with the required properties for this optical application can be achieved only by optimizing the crystal growth process by the aid of numerical simulation. This needs especially a precise calculation of the heat transport and temperature distribution in the solid and liquid $CaF_2$ under crystal growth conditions. As $CaF_2$ is considered to be semitransparent, the internal radiative heat transfer in $CaF_2$ plays an decisive role in the simulation of the heat transport. On the other hand it is very difficult to obtain quantitative experimental data for evaluating numerical models as $CaF_2$ is extremely corrosive at high temperatures. In this work we present a newly developed experimental technique to perform temperature measurements in $CaF_2$-crystal as well as in the melt under conditions of crystal growth process. These experimental results are compared to calculated temperature data, which were obtained by using different numerical models concerning the internal heat transfer in semitransparent $CaF_2$. It will be shown, that an advanced model, which was developed by the authors, gives a much better agreement with experimental data as a standard model, which was taken from the literature.

• Restorative Dentistry and Endodontics
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• v.29 no.5
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• pp.454-461
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• 2004

The purpose of this study is to compare and to evaluate the effects of the degree of saturation on the progression of artificial root caries lesion. A total of 8 human premolars without any defects and cracks selected and the cementum were removed and the teeth were cleaned with ultrasonic device and pumice without fluoride. Each tooth was sectioned into 6 pieces and they were ground with #800 sandpaper until they had a thickness of 200pm. Specimens were applied with nail vanish except for the 2-3 mm window area after application of bonding agent. Under the constant pH, the specimens were divided into 6 groups (degree of saturation: 0.1415, 0.1503, 0.1597, 0.1676, 0.1771. 0.1977). Each group was immersed in acid buffer solution for 1. 2, 3, 5 days under controlled temperature ($25^{\circ}C$) and imbibed in water and examined using the polarizing microscope. The results were as follows 1. Although the degree of saturation of demineralization solution decreased, the depth of penetration in the dentin was constant. 2. Erosion was observed on the surface of all the teeth in the group I, II. In the group III, IV, V, surfaces were not changed. The teeth in the group VI showed the more mineralized surface but not the shape of the dentinal tubules distinctively. 3. In all groups, the lesion progressed rapidly at the first day of the experiment, but increased gradually as time elapsed.

• Journal of Technologic Dentistry
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• v.13 no.1
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• pp.61-78
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• 1991

Dental caries is one of the main factors to cause the teeth to be lost. Diet is the important factor in the development of dental caries. Today, Dental plaque control, Fluoride to pical application, Fissure sealing and Diet control are used to prevent dental caries. By the five day diet diary, the author surveyed the food in take of 600 infants aged from 10 to 12 in the subures of Seoul. Using the cariogenic food intake analysis form, the detergent food intake analysis form and the basic food intake analysis form, the data were collected, analysed and discussed. After discussing the results, the author concluded as follows : 1. The intake frequency of meals per day was 4.91 times, of which 2.74 times taken at meals and 2.17 times at between meals. Girls(5.00) had taken more times than boys(4.69) at meals an between meals. 2. The intake frequency of cariogenic food per day was 1.93 times, Liquid cariogenic food was taken 0.05 times at meals, and 0.58 times at between meals. Solid cariogenic food was taken 0.05 times at meals, and 0.08 times at between meals. Girls(1.67) had taken cariogenic food more times than boys(1.46). 3. The percentage of intake without detergent food of each intake time per head per day was 71.62% at meals, and 85.7% at between meals. The highest percentage was at evening meals. Boys(44.00%) had taken more detergent food than girls(56.71%). 4. Both boys and girls had the basic food intake taken enough only in 2nd group of basic food, lacking in the other 4 groups. Girls had taken the basic food comparatively more times than boys.

• Environmental Engineering Research
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• v.20 no.3
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• pp.223-229
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• 2015

The application of coagulation for feed water pretreatment prior to microfiltration (MF) process has been widely adopted to alleviate fouling due to particles and organic matters in feed water. However, the efficiency of coagulation pretreatment for MF is sensitive to its operation conditions such as pH and coagulant dose. Moreover, the optimum coagulation condition for MF process is different from that for rapid sand filtration in conventional drinking water treatment. In this study, the use of response surface methodology (RSM) was attempted to determine coagulation conditions optimized for pretreatment of MF. The center-united experimental design was used to quantify the effects of coagulant dose and pH on the control of fouling control as well as the removal organic matters. A MF membrane (SDI Samsung, Korea) made of polyvinylidene fluoride (PVDF) was used for the filtration experiments. Poly aluminum chloride (PAC) was used as the coagulant and a series of jar tests were conducted under various conditions. The flux was $90L/m^2-h$ and the fouling rate were calculated in each condition. As a result of this study, an empirical model was derived to explore the optimized conditions for coagulant dose and pH for minimization of the fouling rate. This model also allowed the prediction of the efficiency of the coagulation efficiency. The experimental results were in good agreement with the predictions, suggesting that RSM has potential as a practical method for modeling the coagulation pretreatment for MF.

• Journal of the Korea Convergence Society
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• v.6 no.6
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• pp.131-137
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• 2015

To study the effects of oral health education on children, weekly education sessions and surveys were held for 214 preschoolers, 6-7 years of age, in 2 K-area kindergartens for 4 weeks in July 2015. Statistics on oral health behaviors such as children with regular dental checkups(p<0.05), children who underwent fluoride application(p<0.05), children without dental caries diagnosis(p<0.001), children with mothers who underwent oral health education(p<0.05) showed significant difference. Oral health knowledge scores(6 being perfect) increased from pre-education scores of 4.96 to post-education score of 5.54. oral health behavior scores(11 being perfect) also increased from pre-education scores of 7.18 to post-education score of 7.75(p<0.001). Therefore, it is the author's opinion that the development of oral health education programs with relatively short cycles, alongside systematic, practical, and repeated education would be beneficial.

• Journal of dental hygiene science
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• v.17 no.3
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• pp.202-208
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• 2017

Korea has been running the community oral health program for the elderly, including topical fluoride application and scaling. The aim of this study was to compare the subjective and objective oral health status of 345 participants according to the number of participants in the program and of 37 participants before and after the 5-year program. The survey consisted of an interview questionnaire and oral examinations. Analysis of variance was used to compare the variables of the 345 participants according to the numbers of participants. Paired t-test was used to compare the oral health statuses before and after the 5-year program in 37 subjects. There was no difference in subjective oral health status according to the number of participants in the oral health program in the elderly, including subjective health status, subjective oral health status, satisfaction with oral health, concern about oral health, need of dental treatment, oral pain, tooth sensitivity, subjective periodontal health, and subjective symptoms of periodontitis. The community periodontal index (CPI) of the 1 time participants was significantly higher than that of 3 times, 4 times or 5 times participants in the upper center, lower left, lower center, and lower right areas. There was a significant improvement in CPI from $2.59{\pm}1.14$ to $1.41{\pm}1.54$ (p<0.001) and positive oral behavioral change (daily tooth brushing frequency from $2.27{\pm}0.73$ to $2.54{\pm}0.90$) before and 5 years after the program. However, the program did not prevent tooth loss as the numbers of the remaining teeth significantly reduced from $23.77{\pm}1.84$ to $21.95{\pm}2.03$ over 5 years. We showed that running the community oral health program for the elderly for more than three years might have positive effects on the periodontal health of participants.

• Membrane Journal
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• v.27 no.5
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• pp.458-467
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• 2017

In this study, we prepared PVDF membranes via TIPS for water treatment applications. PVDF was used for its excellent chemical and mechanical properties. The effect of coagulation bath composition, temperature, and heat capacity on the overall membrane morphology was studied and observed using SEM. A mixture of DOP and DBP was used as the diluent, and silica was used as an additive. It was observed that as the heat capacity of the coagulation bath increased, the crystallization rate of PVDF decreased yielding larger pores. Also, as the heat capacity of the coagulation bath decreased, the crystallization rate of PVDF increased yielding smaller pores.

• Journal of the Korean institute of surface engineering
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• v.42 no.3
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• pp.109-115
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• 2009

Magnesium is one of the lightest metals, and magnesium alloys have excellent physical and mechanical properties such as high stiffness/weight ratios, good castability, good vibration and shock absorption. However their poor corrosion resistance, wear resistance, hardness and so on, have limited their application. To improve these defects, many techniques are developed. Micro arc oxidation(MAO) is a one of the surface treatments under anodic oxidation in which ceramic coating is directly formed on the surface of magnesium alloy. In this study, the characteristics of anodic film were examined after coating the AZ31B magnesium alloy through the MAO process. MAO was carried out in potassium hydroxide, potassium fluoride, and various concentration of sodium silicate in electrolyte. The morphology and chemical composition of the coating layer were characterized by SEM, XRD, EPMA and EDS. The hardness of anodic films was measured by micro-vickers hardness tester. As a result, the morphology and composition of anodic film were changed by concentration of sodium silicate. Thickness and Si composition of anodic film was increased with increasing concentration of sodium silicate in electrolyte. The hardness of anodic film was highly increased when the concentration of sodium silicate was above 40 g/l in electrolyte.

• Journal of Technologic Dentistry
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• v.39 no.1
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• pp.55-65
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• 2017

Purpose: The study has been undertaken on several factors that may influence on the orthodontic treatment satisfaction with the subject of male and female university students who have experience in receiving the orthodontic treatment by visiting orthodontic clinic. Methods: This study has implemented questionnaire survey for 350 male and female university students who have experience in receiving the orthodontic treatment by visiting orthodontic clinic due to the mall occlusion, From the 350 questionnaires collected, a total of 291 copies (83.1%) excluding the questionnaires that have inconclusive response or erroneous response is used as the research analysis data Results: The orthodontic treatment satisfaction is significantly higher for students in large cities and mid- to small sized cities than students in rural area, and it was higher for students with mid-economic class that students of upper class and lower class. It is shown for a student that began the orthodontic treatment from the elementary school, a student that had 5 times or more of brushing teeth for each day had significantly higher level of satisfaction that students that are not. In addition, a student that knows well of the oral hygiene management method, a student that had the fluoride application treatment during the orthodontic treatment period and a student that used the toothbrush for orthodontic service had significantly higher level of satisfaction that students that are not. Conclusion: Factors influencing on the orthodontic treatment satisfaction are very diverse and it is considered that it requires effort to improve the quality of medical service and sufficient understanding on several factors to improve the orthodontic treatment satisfaction for patients as well as the encouragement for orthodontic treatment patients of the relevant people in orthodontic clinics that provide the orthodontic clinic service.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.3
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• pp.598-603
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• 1998

Amelogenesis imperfecta is a group of hereditary defects of enamel unassociated with any other generalized defects. The prevalence of this condition has been estimated to range from 1 in 14,000 to 1 in 16,000, depending on the population studied. It may be differentiated into three general types : hypoplastic, hypocalcified, and hypomaturation, depending on the clinical presentation of the defects and the likely stage of enamel formation that is primarily affected. The dentin and root form are usually normal, but the enamel may lack the normal prismatic structure, being laminated throughout its thickness or at the periphery, with the result that these teeth are more resistant to decay. This case is that of an six-year-old girl brought to the pediatric dentistry department by her parents for esthetic reasons and also because of slight dental sensitivity. Clinical and radiographic examinations confirmed amelogenesis imperfecta. The author has treated with the crowning of the primary molars, using prefomed NiCr crowns and periodic fluoride application on whole dentition.