• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1931-1938
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• 2021

Uranium ingot is produced by metallothermic reduction of uranium tetrafluoride using magnesium or calcium as reductant. Presence of oxygen containing compounds viz. uranyl fluoride and uranium oxide in the starting uranium fluoride has a significant effect on the firing time, final temperature of the charge, slag-metal separation and hence the metal recovery. As reported in the literature, the maximum tolerable limit for uranyl fluoride in the UF₄ is 2.5 wt% and limit for uranium oxide content is in the range 2-3 wt%. No theoretical or experimental basis is available till date for these limits. Analyses have been carried out in this study to understand the effect of UO₂F₂ concentration in the starting fluoride on the final temperature of the products and thus the reduction characteristics. UF₄ having uranyl fluoride concentration, less than as well as more than 2.5 wt%, have been investigated. Thermodynamic calculations have been carried out to arrive at a general expression for the final temperature attained by the products during calciothermic reduction of UF₄. Finally, an upper limit for the oxygen containing impurities has been estimated using the CaO-CaF₂ phase diagram.

• 치위생과학회지
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• 제10권5호
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• pp.373-378
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• 2010

불소도포와 치면열구전색은 치아우식을 예방하기 위한 목적으로 임상에서 널리 병용하여 사용되고 있지만, 불소가 치면열구전색제의 표면 구조를 변화시켜 미생물이 서식할 조건을 마련하여 수복물의 수명을 단축시키는 원인이 될 수 있다. 이에 본 연구에서는 현재 치과 임상에서 많이 사용되고 있는 레진계 실란트 Concise와 Eco-S를 사용하였고, 대표적인 불소도포제재 1.23% APF gel과 5% NaF Fluoride Varnish가 치면열구전색제의 표면 구조에 미치는 영향을 평가하기 위해 제작된 치면열구전색제시편을 각각 5군으로 불소제재를 처리하지 않은 I군, APF gel 1분간 처리한 II군, APF gel 4분간 처리한 III군, Fluoride Varnish 1분간 처리한 IV군, Fluoride Varnish 4분간 처리한 V군으로 분류하여 마모실험에 의한 무게변화를 측정하였고, 광학현미경을 이용하여 표면구조를 관찰하여 다음과 같은 결론을 얻었다. 1. 치면열구전색제 Concise를 이용한 마모실험에서 불소제재를 처리하지 않은 I군에 비하여 APF gel 4분간 처리한 III군에 무게 감소가 증가하였으며, Fluoride Varnish 4분간 처리한 V군에서 무게 감소가 적으며(p<0.05), Eco-S를 이용한 마모실험 결과 또한 같았다(p<0.05). 2. 광학현미경으로 표면의 변화를 관찰한 결과 APF gel을 도포한 경우 기질의 소실로 필러가 두드러진 양상을 보였으며, 각 군 별로는 APF gel 4분간 처리한 III군, APF gel 1분간 처리한 II군, 불소제재를 처리하지 않은 I군, Fluoride Varnish 1분간 처리한 IV군, Fluoride Varnish 4분간 처리한 Ⅴ군의 순으로 표면 거칠기가 감소되는 결과를 보였다. 결론적으로, 치면열구전색과 불소도포를 당일 시행하는 경우, 불소도포제를 1.23% APF gel 사용 시 4분 보다 1분 도포하며, 1.23% APF gel보다는 5% NaF Fluoride Varnish 도포하는 것이 치면열구전색제의 표면 구조에 영향을 줄일 수 있다고 사료된다.

• 한국식품과학회지
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• 제22권2호
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• pp.172-176
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• 1990

크릴에 과량 존재하는 불소를 감량시키고자 전기분해 반응에 의한 electrocondensation 방법을 이용하였다. Electrotocondensation 방법에 의한 크릴 불소의 감량정도는 불소이온의 존재형태 (이온 및 결합상태의 불소, 총불소)와 시료의 부위(육질, 키틴질, 건조크릴)에 따라 차이가 있는 것으로 나타났다. 전기분해 반응시간에 따른 불소의 감량곡선을 살펴보면, 반응초기에는 불소의 감량이 빠르게 진행되었으나 일정시간 이후부터는 서서히 감량되는 경향을 나타내어 전기분해반응 120분 후에는 반응전 초기 불소농도의 $30{\sim}70%$ 수준까지 감량시킬 수 있었다. 이상의 결과를 살펴볼 때, electrocondensation 방법으로 크릴에 과량 함유되어 있는 불소를 상당량 제거하였지만. 아직도 많은 양의 불소가 각 시료에 잔재하고 있어, 완전한 불소세거를 위해서는 보다 깊은 연구가 필요로 되는 것으로 생각되었다. 즉 Newman은 세포외 불소가 벼에 집적되는 과정에서 hydroxyl기와의 치환반응을 고찰하였고, Rehbein등은 크릴을 주 먹이사슬로 하는 남극어류의 대부분이 chitinase와 pretense등의 강한 효소활성으로 크릴을 소화하는 과정에서 불소가 유리되어 체외로 방출되는 것으로 고찰하고 있어, 불소의 이동기작 및 집적과정에 대한 깊은 연구와 더불어 electrocondensation 방법을 보다 효율적으로 이용할 수 있는 방안이 모색된다면 크릴의 불소문제는 완전히 해결될 수 있을 것으로 생각되었다.

• 대한소아치과학회지
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• 제23권2호
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• pp.306-326
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• 1996

The purpose of this study was to compare the enamel fluoride uptake and anticariogenic effect following topical application with different physical form of fluoride and application time. The results can be summarized as follows: 1. While the 4-minute applicaton increased the enamel fluoride uptake significantly than 1-minute application regardless of physical form of applied topical fluoride agents, no siginificant difference could be found between foam and gel type when applied for the identical period of time. 2. The application time or the physical form of topical agents had no singificant influence on the reduction of caries lesion. 3. Based upon the above-mentioned results of this study, it cannot be concluded that the amount of enamel fluoride uptake has an absolute impact on the change of lesion depth. Therefore, the clinical application of 1-minute topical fluoride application which appears to have a similar anticariogenic efficacy to 4-minute fluoride application may be encouraged.

• Journal of Oral Medicine and Pain
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• 제21권2호
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• pp.207-224
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• 1996

This study was designed to determine the most effective concentration of fluoride and energy density of laser irradiation for the anticarious effect. For this study surface hardness in enamel was measured before and after irradiation with pulsed Nd;YAG laser and the topical application of fluoride. Of the permanent mandibular anterior hovine teeth, healthy, carious free ones were used. Three hundred specimens were made. Specimens within 25~45 Vickers hardness numbers were assigned to 20 control and experimental stoops ; each containing 15 specimens. After forming artificial carious lesions, 10 J/$\textrm{cm}^2$, 20 J/$\textrm{cm}^2$, and 30 J/$\textrm{cm}^2$ energies were irradiated on the enamel surface of each experimental group. Also NaF, NH4F, Elmex gel(amine fluoride) and APF gel fluoride compounds were applied topically. Next, all the specimens were placed into the pH circulatory procedures for eight days. Vickers hardness numbers were measured using a microhardness tester. Surface changes of the enamel were observed using an scanning electron microscope. The comparative ana1ysis yielded the following results : 1. The reduction of surface hardness of the enamel surface was less in all groups with fluoride application than in the group without fluoride application. 2. The APF gel croup with 10 J/$\textrm{cm}^2$ irradiation showed the lowest reduction of surface hardness. 3. The reduction of surface hardness of the enamel surface in the group of laser irradiation without fluoride application not showed any significant difference according to the energy density of the laser. 4. Under the scanning electron microscope, in enamel irradiated with 10J/$\textrm{cm}^2$ showed appearance similar to acid etching surface. In enamel irradiated with 20 J/$\textrm{cm}^2$, line enamel crack was detected. In enamel irradiated with 30j/$\textrm{cm}^2$, severe enamel crack and fusion of enamel were detected. These results suggest that one could obtain the best anticariogenic effects without damage to teeth in the group of application of APF gel after laser irradiation with 10 J/$\textrm{cm}^2$.

• Fisheries and Aquatic Sciences
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• 제15권3호
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• pp.203-207
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• 2012

The amount of fluoride removed from Antarctic krill via organic acid extraction depends on the extraction time, concentration, extraction volume, and the nature of the acid itself. The fluoride content in Euphausia superba was determined by measuring the concentration of fluoride ion in acidic extracts using an ion-selective electrode. The best results were obtained by adding 50 mL of 0.01 M citric acid to 0.3-0.5 g of krill and extracting for 5 min. Under these conditions, recoveries of fluoride from frozen whole krill and krill meat were 95.6-99.5% and 97.5-101.3%, respectively. The dry basis fluoride contents of krill by-product, krill meat and the boiled krill were 705, 298, and 575 ppm, respectively. These levels were significantly reduced by citric acid extraction.

• Restorative Dentistry and Endodontics
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• 제16권1호
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• pp.216-225
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• 1991

The purpose of this study was to evaluate the desensitizing effect of potassium oxalate(Group I), sodium fluoride (Group II), and control group (Group III). The 120 teeth of 26 patients who had been complained dentinal hypersensitivity were divided into three groups by applicating agent. The observation was done before and immediately after treatment. The data were statistically analyzed and the results were as followed. 1. Potassium oxalate showed the best desensitizing effect to the stimuli, followed by sodium fluoride, control group, and there was a significant difference (p<0.05) in desensitizing effect among the groups. 2. Potassium oxalate showed the best desensitizing effect to the stimuli, followed by sodium fluride, control group on both cervical abrasion and gingival recession, and there was a significant difference (p<0.05) in desensitizing effect among the groups on both cervical abrasion and gingival recession. 3. There was no significant difference (p<0.05) in effect of the desensitization between cervical abrasion and gingival recession. 4. The scratch and air blast I were more effective in desensitiziation than other stimuli with significant difference (p<0.05). In view of the results mentioned above, it can be conceived that potassium oxalate is more effective than sodium fluoride on the reduction of dentinal hypersensitivity.

• Restorative Dentistry and Endodontics
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• 제22권2호
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• pp.575-595
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• 1997

Replacement resorption is followed by the delayed replantation of an avulsed tooth. Currently no effective treatment is substantiated for replacement resorption. The purpose of this study was to investigate the effect of stannous fluoride, bisphosphonate (etidronate disodium) and gallium nitrate, which have been shown to reduce dentin resorption, on human dentin. Osteoclasts were collected from tibeas of chick embryo. The cells were well agitated to prevent adhesion and seeded onto the sliced human dentin wafers which had been soaked in either culture media (control), or several different concentrations of stannous fluoride, etidronate disodium (l-hydroxyethylidene -1,1-bisphosphonate disodium), and gallium nitrate. Resorption was measured by counting the number of resorptive pit produced by the cells. Results are as follows. Stannous fluoride and etidronate disodium showed statistically significant reduction of dentin resorption(p<0.05) but the effect of stannous fluoride seemed to be its high cytotoxicity. Etidronate disodium did not show cytotoxicities in all experimented concentrations. Gallium nitrate did not show differences in resorption either between different concentrations or from the control group.

• Environmental Analysis Health and Toxicology
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• 제13권1_2호
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• pp.19-26
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• 1998

In Korea, fluoride was first introduced into the drinking water of residents of Jinhae, KyungNam in 1981 for the prevention of dental caries. Ever since, growing numbers of communities favor fluoridation. The mechanism of F prevention of tooth decay is well known: fluoride ions substitute for hydroxyl ions in hydroxyapatite of hard tissues, which result in crystal perfection, with consequent reduction in dental caries. Soluble fluorides such as sodium fluoride are almost completely absorbed from the gastrointestinal tract. However, the presence of divalent or trivalent cations such as aluminum, magnesium, and calcium that can complex with F can reduce the degree of absorption. In U.S.A., over 7000 communities are now adding F to their drinking water. However, some portion of population oppose fluoridation, voicing both concern about the safety of fluoridation as well as for personal choice. Thus, This paper reviews the interaction of fluoride and cations as well as fluoride and suggests possible problems associated with fluoridation, a controversial issue.

• Journal of Korean Academy of Oral Health
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• 제42권4호
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• pp.118-123
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• 2018

Objective: This study aimed to investigate the effects of fluoride-containing acidic tea beverages on bovine teeth surfaces. Methods: The pH values and fluoride concentrations of 11 kinds of mineral water and 23 kinds of tea were measured. The fluoride-containing Seopyenje black tea beverages with pH 3.48 were chosen for the experimental group. Distilled water that did not contain fluoride and had the same pH value as that of the Seopyenje black teas served as the positive control. The Jeju Samdasoo mineral waters with neural pH (pH 7.52) and no fluoride were chosen as the negative control. Bovine teeth in each group were submerged for 10 minutes. Thereafter, surface microhardness of each bovine teeth was measured and the results were analyzed. Results: The pH value range was 6.94-8.09 ($mean=7.37{\pm}0.08$) for the 11 kinds of mineral water and 3.48-6.74 ($5.62{\pm}0.05$) for the 23 tea beverages. Titratable acidity of the Seopyenje black tea beverages was higher than that of the distilled water mixed with citric acid, and the pH was 5.5 and 7.0, respectively. The fluoride content of the 11 kinds of mineral water was 0-1.09 ppm ($mean=0.44{\pm}0.02ppm$) that of the 23 tea beverages was and 0-0.74 ppm ($0.64{\pm}0.06ppm$). In terms of enamel microhardness reduction of the bovine teeth, the tea beverages had the largest effects. There was no significant difference in microhardness reduction between the tea beverages and distilled water mixed with citric acid (P>0.05). Conversely, a significant difference was found between the kinds of mineral water and tea beverages, and also between mineral water and distilled water mixed with citric acid (P<0.05). Conclusions: Acidic tea beverages appeared to erode the surfaces of bovine teeth. The amount of fluoride in the tea beverages was not enough to inhibit erosion. Therefore, frequent intakes of acidic tea beverage are likely to increase erosion on the surfaces of bovine teeth, by affecting the enamel microhardness of teeth.