• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.6
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• pp.219-224
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• 2022

CaF₂ single crystal has a large band gap (12 eV), and it is used for optical windows, prisms, and lenses due to its excellent transmittance in a wide wavelength range and low refractive index. Moreover, it is expected to be one of the materials for ultraviolet transmissive laser optical components. CaF₂ belongs to the fluoride compounds and has a face-centered cubic (FCC) structure with three sub-lattices. The representative method for CaF₂ single crystal growth is Czochralski, which method has the advantages of high production efficiency and the ability to make large crystals. In this study, X-ray diffraction (XRD), X-ray rocking curves (XRC) measurement, and chemical etching were performed to analyze the crystallinity and defect density of the CaF₂ single crystals, grown by the Czochralski method. Fourier-transform infrared spectroscopy (FT-IR) and UV-VIS-NIR spectroscopy systems were used to investigate the optical properties of the CaF₂ crystal. The provability of various applications, including UV application, was systematically investigated with various analysis results.

• 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.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.5
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• pp.551-564
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• 2003

Statement of problem : Magnesium oxide may increase pH of alginate, and supply magnesium ions to the polymerization reaction of alginate. Purpose : This study was designed to evaluate the influence of incorporation of magnesium oxide to alginate composition. Material and Method : Seven kinds of experimental alginates were prepared and used for the experiments. Components with unchanging concentrations were sodium alginate 15%, calcium sulfate 14%, sodium phosphate 2%, and zinc fluoride 3%. Contents of magnesium oxide were varied as 0%, 1%, 2%, 3%, 4%, 5%, 6%. Diatomaceous earth were added to each experimental groups as balance to be 100%. Control group was a MgO 0% group. Working time, setting time, elastic recovery strain in compression, compressive strength and tear resistance were measured were measured. Sample size for each groups were 10. Arithmetic means were used as each groups representative values. Regression test between MgO contents and results, Duncan's multiple range test, and One-way ANOVA test were done between groups at level of 0.05. Results : 1 Magnesium oxide made the working time and setting time as longer(p<0.0001). 2 Magnesium oxide did not alter the elastic recovery(p>0.05). 3. Magnesium oxide contents between 2% and 4% exhibited the lowest strain in compression on alginates(p<0.0001). 4. Magnesium oxide made the compressive strength and the tear resistance stronger(p<0.0001). Conclusion : These results mean that setting time of alginate maybe controlled and that mechanical properties maybe improved by the incorporation of magnesium oxide into alginate, without any reduction of elasticity.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.2
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• pp.243-257
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• 2003

The purpose of this study was to search the influences of the increase of the contents of sodium alginate in the experimental alginates on the some mechanical properties. 3 commercial alginates were selected for the purpose of comparison of the results of experiments. 7 experimental alginates were manufactured with the rise of contents of sodium alginate from 8.8% to 18.3% with the decrease of contents of diatomaceous earth and with the constant contents of calcium sulfate 12.5%. sodium phosphate 2.2%, zinc fluoride 2.0%. Splitable metal mold with 12.5mm diameter and 20.0mm height was filled with mixed alginate to prepare the cylinder shaped specimens. Strain in compression, elastic recovery, compressive strength were tested using the ISO specification number 1563, alginate impression material. Experimental groups were 7, and 10 specimens were used for each test items and each groups. Following results were obtained ; 1. Strain in compression was decreased with the increase of sodium alginate contents (p=0.0077, r2 = 0.6302). 2. Elastic recovery was decreased with the increase of sodium alginate contents but was not significant(p=0.0639, r2=0.7449). 3. Compressive strength was increased with the increase of sodium alginate contents (p<0.0001, r2 = 0.9617). These results mean that the increase of sodium alginate contents make alginate harder but may result the increased permanent deformation.

• Archives of Plastic Surgery
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• v.34 no.4
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• pp.471-477
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• 2007

Purpose: Hydrofluoric acid(HF) is one of the most dangerous mineral acids with dissociated fluoride ions. As hydrofluoric acid is present in various household products(such as rust removers), a large population of industrials is at the risk of HF exposure. It is a very strong organic acid, used widely in glass etching, metal washing, and in the semiconductor industry. Even when using adequate safety measures, lack of care on the user's part results in chemical burn by HF. Symptoms caused by HF-induced chemical burns shows delayed manifestations resulting in a loss of proper treatment opportunities. We therefore reviewed 20 cases of HF-induced chemical burns and treatment principle. Methods: The objects of this study were 19 male patients and 1 female treated from March 2004 to March 2006. There were 19 cases of injury on digits and 1 on the wrist area. There were 15 cases of immediate treatment after sustaining HF-induced burns, and 5 cases of delayed treatment. As a principle, in the emergency treatment, partial or complete removal of the nail along with copious washing with normal saline was done, depending on the degree of HF invasion of the distal digital extremities. Results: The 15 cases who came to the hospital immediately after the injury were healed completely without sequelae, and those who delayed their treatment needed secondary surgical measures, due to the severity of inflammation and necrosis of the digital tissues. Conclusion: As the industrial sector develops, the use of HF is increasing more and more, leading to increase in incidences of HF-induced chemical burns. When treating chemical burns caused by HF, washing by copious amounts of normal saline, along with early removal of the nails, rather than calcium gluconate, seems to be a available method for preserving the shape and function of the digits and the nail. The education of patients regarding this subject should be empathized accordingly.

• Journal of Korean Dental Science
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• v.16 no.1
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• pp.74-79
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• 2023

Purpose: Cention N (Ivoclar Vivadent) was a recently introduced alkasite-based restorative material that was expected to replace amalgam and glass ionomer cement. This material was an esthetic restoration with adequate mechanical strength and release of fluoride and calcium. The purpose of this study was to measure the water sorption and water solubility of Cention N and evaluate its long-term durability compared to other esthetic restorations (Resin-Modified Glass Ionomer cement [RMGIC], Giomer, Composite Resin). Materials and Methods: Twenty specimens each of Cention N (CN), Resin Modified-Glass Ionomer Cement (FJ), Giomer (BF), and Composite Resin (FZ) were made. After each specimen was completely dried in a desiccator for 24 hours using a vacuum pressure pump, the specimen was weighed (m1). After that, the specimen was immersed in distilled water at 37℃ for 7 days, stored in a drying oven, and weighed (m2). After drying completely for 24 hours in a desiccator, the specimen was weighed (m3) to calculate the water absorption and water solubility using Formulas 1 and 2. The measured values were statistically processed and analyzed using SPSS, and the significance level was set at 0.05. Result: When measuring water sorption, FJ (122.61 ㎍/mm³) showed significantly higher water sorption than CN (35.42 ㎍/mm³) (P<0.05). There was no significant difference between FZ (18.03 ㎍/mm³) and BF (14.76 ㎍/mm³) (P=0.930). When measuring water solubility, CN (6.65 ㎍/mm³) showed significantly higher water solubility than FJ (1.47 ㎍/mm³) (P<0.05). Conclusion: Cention N had lower water sorption than RMGIC, but higher water solubility, indicating that it is more vulnerable to moisture and has lessened long-term durability.

• Journal of dental hygiene science
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• v.16 no.2
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• pp.176-182
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• 2016

The purpose of this study was to evaluate the in-vitro efficacy of the active ingredients of dentifrice following treatment time. The whitening effect was evaluated by a change in lightness value relative to the contact time of hydrogen peroxide, by using artificially stained hydroxyapatite discs. The anti-calculus effect was assessed based on the amount of calcium eluted from the human dental calculus by sodium pyrophosphate. Remineralization was evaluated by the Vickers hardness test following the application of sodium fluoride to bovine enamel. In order to view dentinal tubules occlusion, the formation of insoluble calcium salts by bovine dentin specimens was observed using scanning electron microscopy. Change in lightness value (${\Delta}L$) was $5.50{\pm}1.51$ after 1 min of treatment, $5.73{\pm}0.43$ after 3 min, $8.64{\pm}0.24$ after 10 min, $18.93{\pm}0.76$ after 30 min, and $27.35{\pm}0.54$ after 60 min. The amount of calcium eluted from the human dental calculus was $4.23{\pm}0.14ppm$ after 1 min of treatment, $4.51{\pm}0.04ppm$ after 3 min, $12.12{\pm}0.16ppm$ after 10 min, $17.85{\pm}0.81ppm$ after 30 min, and $25.15{\pm}0.32ppm$ after 60 min. The Vickers hardness change value (${\Delta}VHN$) was $1.96{\pm}1.44$ after 1 min, $1.52{\pm}1.06$ after 3 min, $9.06{\pm}0.15$ after 10 min, $10.83{\pm}5.13$ after 30 min, and $12.55{\pm}2.09$ after 60 min. Partial dentinal tubules occlusion was observed at 10 min and complete occlusion was evident at 60 min. In summary, the use of patch type dentifrices for 10, 30, or 60 min were 1.57 to 8.26 times more effective than using the paste type dentifrices for 1 to 3 min. Based on these findings, it is reasonable to expect that the use of patch type dentifrices for 10 min would lead to remineralization, anti-calculus and dentinal tubules occlusion effects, and that use for 30 min would result in a whitening effect.

• Journal of Periodontal and Implant Science
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• v.29 no.2
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• pp.401-415
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• 1999

Root surfaces affected by periodontal disease undergo various forms of changes. Cementum exposure from gingival recession may result in absorption of calcium, phosphorus, and fluoride and subsequent hypermineralization and increased radiodensity. Although some reports have suggested that inorganic content with root cementum might show various changes depending upon age or extent of periodontal disease, but no consensus can be reached regarding the the distribution of various elements. The present study examines the difference in mineral content between healthy and periodontal diseased roots by analyzing three areas per tooth along the root surface in cervico-apical direction using electron probe and scanning electron microscope. Healthy tooth that was extracted for orthodontic purpose was used as control. Experimental teeth include those with periodontal pocket depth exceeding 6mm and those with gingival recession and periodontal pocket depth of 2-4mm. Levels of Ca, P, Mg and Na were measured using wavelength dispersive x-ray spectrometer at three areas per tooth. The examined areas were located apical to cemento-enamel junction in control and periodontal ligament-depleted areas in experimental teeth. The corresponding areas were also examined with scanning electron microscope(x70) The results are as follows. 1. Minerals were detected in order of Ca, P, Mg and Na. In all root surfaces, levels of Ca and P were higher in dentin than in cementum. 2. Level of Mg was twice as high in dentin than in cementum. There was no significant difference in the level of Mg and Na between normal and periodontal diseased roots or between the various locations in the same root. 3. Level of Ca and P in the surface cementum showed no difference between normal and periodontal diseased root, although the areas in dentin with high level of either ion also showed high level of corresponding ion in cementum. 4. Difference in the Ca and P content between various locations within the same root was noted, although no coherent pattern existed. These results suggest that although the mineral content of the root cementum in periodontitis-affected tooth is affected by exogenous ions from saliva and food, but there was no difference in the mineral contents between normal and periodontally diseased root.

• Journal of Korean society of Dental Hygiene
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• v.3 no.1
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• pp.25-43
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• 2003

In Korea, changes in children's diet patterns accelerate their physical growth and development: frequent snacking has been presumed to be a major cause of increasing dental caries. The present study attempts to clarify the relationship between the physical development of growing children and their tooth decay. For this purpose, 632 six-grade children in 4 elementary school located in Urban(Seoul) and Rural(Po-gok, Yang-In) were classified into three groups based on the Weight Length Index(WLI), known to reflect the nutritional conditions of school-age children, and the relationship was analyzed between each group and the variables considered to be related with dental caries. The result is as follows: The average weight and height of the male is $44.88{\pm}10.89$ kg, $148.49{\pm}7.33$ cm and female is $43.35{\pm}9.60$ kg, $149.23{\pm}6.73$ cm, respectively, which are in the similar level with the Korean Physical Standard. The classification of the children by the WLI reveals a relatively high distribution of over-weighted child ren - 212 persons, 335% of the entire population. The DMFT Index was a little high in the rural area(3.15 teeth in urban and 3.31, in rural). Among the groups of children classified by the WLI, the over-weight group have the highest DMFT index(3.69 teeth). The relationship between the frequency of taking in basic nutrients and the DMFT index is also found: the relationship is not evident in case of the foods containing rich calcium, protein, as well as fruits and vegetables. But, in the protein-rich food, higher frequency of its intake means significantly lower DMFT index in the normal-weight group of the urban children. In case of carbohydrate, higher frequency of its intake means significantly higher DMFT index in all the groups of the rural children. The DMFT index has some correlations with the relevant variables: the index has a positive correlation with the frequency of snacking, and a negative correlation with the economic status. That is, the higher the frequency of snacking is, and the lower the economic status is, the higher the DMFT index may be. In the logistic multiple regression analysis conducted with the presence of DMFT as a dependent variable, only the frequency of tooth brushing is turned to be a variable affecting the presence of either decayed, missing, or filled teeth. Based on the above result, the variables affecting the DMFT index are a time spent on eating, frequency of intake of protein and carbohydrate for a week, frequency of snacking, regular dental check-ups, preventive behaviors for oral health(fluoride gargling, tooth brusing after each meal, proper tooth brushing method). These variables have a relationship with the DMFT index, but the degree is somewhat different between the groups classified either by the region or by the WLI. Therefore, appropriate nutrition management should be conducted according to the individual's nutritional conditions when the services like nutritional education are provided based on the closely-examined characteristics of each target group. And, at the same time, oral health education should be strengthened, and its importance should also be emphasized so that people can pay attention to their own oral health.

• Journal of the Korean Applied Science and Technology
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• v.35 no.3
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• pp.848-856
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• 2018

The aim of this study was to investigate the hematology and serum chemistry values on Sprague-Dawley rats, used krill (Euphausia superba) meal diet and sodium fluoride (NaF) for 5 weeks. Seven-week-old male rats were divided into five groups and fed experimental diets containing three krill meal contents, administrated orally 10 mg of NaF, basal diet group (BG), basal diet plus 10 mg of NaF group (BFG), 10.0% krill meal plus 10 mg of NaF group (KMF10), 20.0% krill meal plus 10 mg of NaF group (KMF20), and 30.0% krill meal plus 10 mg of NaF group (KMF30). Concentrations of non-esterified fatty acid (NEFA), blood urea nitrogen (BUN), creatinine in sera were significantly lower in the KMF10, KMF20, KMF30 than BFG (p<0.05). In uric acid concentration KMF10 showed no significant difference with the BFG group, was significantly lower than KMF20 and KMF30 (p<0.05). Total calcium (T-Ca) concentrations was all observed to be no significant difference, was increased with krill meal content (p<0.05). Phosphorus (Pi) concentration was no change in the content of krill meal. Accordingly, krill meal was considered to be effective in improving NEFA and BUN, creatinine, uric acid concentration.