• The korean journal of orthodontics
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• v.31 no.2 s.85
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• pp.261-270
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• 2001

The purpose of this study was to evaluate the clinical usefulness of plasma arc light which can reduce the curing time dramatically compared by shear bond strengths and failure patterns of the brackets bonded with visible light in direct bracket bonding. Some kinds of brackets were bonded with the Transbond$^{\circledR}$ to the human premolars which were embedded in the resin blocks according to the various conditions. After bonding, the shear bond strength was tested by Instron universal testing machine and in addition , the amount of residual adhesive remaining on the tooth after debonding was measured by the stereoscope and assessed with adhesive remnant index(ARI). The results were as follows : 1. When plasma arc light was used for bonding the brackets, the shear bond strength was clinically sufficient in both metal and ceramic brackets, but resin brackets showed significantly lower bond strength but which was clinically useful. 2. When metal brackets were bonded using visible light, there was no significant difference in shear bond strength due to the light-curing time and the bond strength was clinically sufficient. 3. When the adhesive failure patterns of brackets bonded with plasma arc light were observed by using the adhesive remnant index, the bond failure of the metal and resin bracket occurred more frequently at bracket-adhesive interface but the failure of the ceramic bracket occurred more frequently at enamel-adhesive interface. 4. There was no statistically significant difference of the shear bond strength and adhesive failure pattern between metal bracket bonded for 2 seconds by curing with plasma arc light and 10 seconds by curing with visible light. 6. When metal brackets were bonded using plasma arc light, the shear bond strength decreased as the distance from the light source increased. The above results suggest that plasma arc light can be clinically useful for bonding the brackets without fear of the decrease of the shear bond strength.

• The korean journal of orthodontics
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• v.39 no.4
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• pp.234-247
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• 2009

Objective: The purpose of this study was to evaluate the shear bond strength of rebonded ceramic brackets according to each condition and find an appropriate method to rebond ceramic brackets with proper shear bond strength in clinical practice. Methods: The study consisted of 12 experimental groups, according to the types of brackets, debonding methods, and treatment methods of the bracket base. Shear bond strength was measured, and adhesive residues left on the tooth surface were assessed. The base of the bracket was examined under scanning electron microscopy. Results: The shear bond strength of the monocrystalline ceramic bracket group was significantly higher than thatof the polycrystalline bracket group with only sandblasting (p < 0.05). There was no significant difference in shear bond strength between groups that used rebonded brackets which were debonded with shear force and debonded with laser (p > 0.05). The shear bond strength of the sandblasted/silane group was significantly higher than that of the selectively grinded group with a low-speed round bur and the sandblasted only group (p < 0.001). The retentive structure was more presented in groups where laser was applied than in groups where shear force was applied to debond brackets prior to rebonding. The bracket bases which were treated before rebonding presented smoother surfaces than new brackets. Conclusions: Shear bond strength could be increased by applying a silane coupling agent after sandblasting before rebonding. Also, the bond strength of the selectively grinded group with a low-speed round bur and the sandblasted group showed acceptable bond strength for clinical orthodontic treatment.

• Journal of Korean Ophthalmic Optics Society
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• v.21 no.1
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• pp.1-10
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• 2016

Purpose: The study was aimed to suggest the most effective color of the tinted lenses by evaluating the effect of the prescription with tinted lenses on the visual quality of the elderly at the age of the sixty or more. Methods: The visual acuity of fifty subjects at the age of sixty or more (17 males, 33 females with the averaged age of $71.0{\pm}6.3$) were corrected to have the visual acuity at a far distance of 0.5 or more using a trial lens frame, and non-tinted, brown-tinted, and gray-tinted lenses were randomly applied on the trial frame. The minimum legibility and minimum separability were measured at a far distance in the aspect of the visual acuity and calculated as LogMAR and then, the visual acuity was compared. The stereopsis and contrast sensitivity were also estimated at a near distance in the aspect of the visual function. The participants' preference for tinted lenses and their subjective symptoms of the visual perception and the movement were further surveyed. Results: The best minimum legibility and minimum separability was shown when wearing non-tinted lenses, and brown-tinted and gray-tinted lenses were in the next. The stereopsis and the contrast sensitivity at a near distance and the visual perception was the best when wearing brown-tinted lenses. It was surveyed that the subjective discomfort was the biggest when wearing gray-tinted lenses, and brown-tinted lenses were the best in the aspect of the subjective preference. Conclusions: As the result of this study, it was revealed that the visual acuity and visual function could be improved by the use of tinted ophthalmic lenses however, its change of visual acuity and visual function was not completely correlated with the subjective satisfaction. Therefore, the appropriate color of ophthalmic lenses should be selected in accordance with the individual visual perception and the main vision lifestyle in the elderly generation. From the present study, the use of non- or brown-tinted lens and brown- or gray-tinted lens can be recommended for distance work and near work, respectively, in the elderly generation under the illumination of about 1,000 lux.

• Korean Journal of Soil Science and Fertilizer
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• v.33 no.6
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• pp.405-415
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• 2000

To determine application rate of elemental sulfur to adjust pH of alkaline soil, buffer curve method was investigated. The elemental sulfur required to control pH 8.3 to pH 6.3 by buffer curve calculation was treated in two soils of silty loam and sandy loam, and the sulfur-mixed soils were moistened with 50% of water holding capacity during incubation of 6 weeks at $30^{\circ}C$. Soil pH was lowered with incubation and reached to target point after 4 weeks of incubation, and elemental sulfur was oxidised entirely to sulfate. This means that buffer curve has the accuracy to determine sulfur application rate in alkaline soil. However it is estimated that application rate of sulfur should be carefully determined in the field scale. Excess application of elemental sulfur resulted in extremely low soil pH and caused the hinderance of lettuce growth by nutritional imbalance and ion toxicity. To simplify the determination procedure of sulfur requirement, buffer curve method by addition of 0.1N-HCl solution as unit of mL was developed, it was compared with theroutine methods which diluted $H_2SO_4$ solution and $Ca(OH)_2$ are added as cmolc per kg soil to adjust each pH step. Buffer capacities, cmolc kg $soil^{-1}$ $pH^{-1}$, calculated from two buffer curves were not significantly different. The result indicates that buffer curve method by 0.1N-HCl can be used to adjust high pH of alkaline soil.

• The korean journal of orthodontics
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• v.38 no.4
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• pp.275-282
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• 2008

Objective: The purpose of this study was to investigate the effect of using laser for ceramic bracket bonding of porcelain surfaces and to compare it with conventional treatment of porcelain surfaces. Methods: Ninety feldspathic porcelain specimens were divided into 9 groups of 10, with each group having different surface treatments performed. Surface treatment groups were orthophosphoric acid, orthophosphoric acid with silane, hydrofluoric acid, hydrofluoric acid with silane, sandblasted, sandblasted with silane, laser etched, laser etched with silane, and glazed surface served as a control group. In the laser etched groups, the specimens were irradiated with 2-watt superpulse carbon dioxide ($CO_2$) laser for 20 seconds. Ceramic brackets were bonded with light-cure composite resin and all specimens were stored in water at $37^{\circ}C$ for 24 hours. Shear bond strength was determined in megapascals (MPa) by shear test at 1 mm/minute crosshead speed and the failure pattern was assessed. For statistical analysis, one-way ANOVA and tukey test were used. Results: Statistical analysis showed significant differences between the groups. The HFA + S group showed the highest mean shear bond strength ($13.92{\pm}1.94\;MPa$). This was followed by SB + S ($10.16\;{\pm}\;1.27\;MPa$), HFA ($10.09\;{\pm}\;1.07\;MPa$), L + S ($8.25\;{\pm}\;1.24\;MPa$), L ($7.86\;{\pm}\;0.96\;MPa$), OFA + S ($7.22\;{\pm}\;1.09\;MPa$), SB ($3.41\;{\pm}\;0.37\;MPa$), OFA ($2.81\;{\pm}\;0.37\;MPa$), G ($2.46\;{\pm}\;1.36\;MPa$), Bond failure patterns of HFA and silane groups, except L + S, were cohesive modes in porcelain while adhesive failure was observed in the control group and the rest of the groups. Conclusions : A 2-watt superpulse $CO_2$ laser etching of porcelain surfaces can provide a satisfactory result for porcelain surface treatment for ceramic bracket bonding. Laser irradiation may be an alternative conditioning method for the treatment of porcelain surfaces.

• Journal of Periodontal and Implant Science
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• v.29 no.2
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• pp.289-297
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• 1999

최근 생약 추출물의 항균, 항염효과에 관한 관심이 증대되고 있으며 이를 이용한 치주질환의 예방 및 억제효과에 관한 연구들이진행되고 있다. 이 연구의 목적은 시험관 실험을 통하여 이미 밝혀진 후박 및 대조추출물의 치주질환 원인 균에 대한 항균, 항염효과를 성견에서 인위적으로 치주질환을 일으킨 후 실험 약제의 경구투여를 통하여 질환의 진행에 미치는 영향을 알아보는 것이다. 실험동물은 생후 18개월된 비글견 6마리를 이용하였다. 상악은 제2,3 소구치 및 제4소구치에 하악은 제2, 3, 4 소구치 및 제1 대구치를 실험대상 치아로 하였으며 교정용 철사와 봉합사를 이용하여 치경부주위에 결찰하여 인위적 치주질환을 일으켰다. 염증 유발 8주 후에 결찰을 풀고 실험동물을 아무 것도 투여하지 않은 군(음성대조군, 3마리), 후박 및 대조 추출혼합물 투여군(실험군, 3마리)으로 나누었다. 실험 시작 (-8주), 약제 투여 시작(0주), 투여 후 2, 4, 6, 8주째에 치태지수, 치은지수, Florida Probe를 이용한 치주낭깊이 및 치은열구액 등의 임상지수를 측정하였다. 염증유발 8주동안에 치태지수, 치은지수, 치주낭깊이, 치은열구액은 급속히 증가하였다. 결찰은 제거하고, 약제를 투여한 이후 실험군에서 치은지수, 치주낭깊이, 치은열구액은 가장 높은 값을 나타내고 있었다. 실험군에서는 8주가 될때까지 임상지수 수치가 낮아지고 있었으며, 8주째에는 대부분의 지수에서 음성대조군과 유의성 있는 차이를 보이고 있었다. 양성대조군에서 비해서 실험군은 대부분의 경우에 임상지수가 나이지고 있었지만 6주 또는 8주째의 치은지수, 치주낭깊이 중 일부만을 제외하고는 유의성 있는 차이를 보이지는 않았다. 이 연구결과 후박 및 대조 추출혼합물이 in vitro뿐만 아니라 in vivo 상태에서도 치주염의 치료 및 골재생의 효과가 있음을 알 수 있었으며, 이와 같은 동물실험의 결과를 바탕으로 임상시험을 거쳐 향후 사람에게 유용한 치주염치료제로 개발, 사용될 수 있을 것으로 여겨진다.

• Journal of the korean academy of Pediatric Dentistry
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• v.37 no.4
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• pp.422-428
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• 2010

Giomer is fluoride-releasing, resin-based dental materials that comprise PRG(pre-reacted glass ionomer) filler. The purpose of this study was to evaluate the shear bond strength of Giomer using self-etching primer systems to bovine dentin. Bovine incisors were mounted in self-curing orthodontic resin and the facial surfaces were wet ground on SIC paper to expose the dentin. Total 100 samples were made and divided randomly into 4 groups, Giomer group(I), Composite resin group(II) and Compomer group(III), Giomer and single bottle adhesive group(IV). The shear bond strengths of 25 samples per each group were measured using universal testing machine. And data were analyzed statistically with One-way ANOVA and Scheffe test. Giomer group(I) showed the significantly higher bond strength than Compomer group(III)(p<0.05). There was no significant difference between Giomer group(I) and Composite resin group(II)(p>0.05). And there is no significant difference between gourp(I) and group(IV). Based on the results of present study, the use of Giomer as an esthetic restorative material for primary teeth might be justified. It is considered that more study about the fluoride releasing ability is needed to evaluate the anticariogenic effect of giomer.

• Journal of the Korean Institute of Gas
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• v.1 no.1
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• pp.106-112
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• 1997

This study measured the ignition limits of methane-air, propane-air, ethylene-air, and hydrogen-air mixture gases by discharge spark of D.C. power resistive circuit. The used experimental device is the IEC type spark ignition test apparatus, it consists of explosion chamber and supply -exhaust system of mixture gas. Mixture gases (methane-air, propane-air, ethylene-air, and hydrogen-air) were put into explosion chamber of IEC type spark ignition test apparatus, then it was confirmed whether ignition was made by 3,200 times of discharge spark between tungsten electrode and cadmium electrode. The ignition limits were found by increasing or decreasing the value of current. For the exact experiment, the ignition sensitivity was calibrated before and after the experiment in each condition. The ignition limits were found by changing the value of concentration of each gas-air mixture in D.C. 24 [V] resistive circuit. As the result of experiment, it was found that the minimum ignition limit currents exist at the value of methane-air 8.3 [$Vol\%$], propane-air 5.25[$Vol\%$], ethylene-air 7.8 [$Vol\%$], and hydrogen-air 21[$Vol\%$] mixture gases. For each the minimum ignition concentration of gases, the relationships between voltage and minimum ignition current were found. The results are as follows. - The minimum ignition limits are decreasing in the order of methane, propane, ethylene, and hydrogen. - The value of ignition current is inversely proportional to the value of source voltage. - The minimum ignition limit currents increase sharply at more than 2 [A]. The reason is caused by overheating the electrode.

• Journal of Astronomy and Space Sciences
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• v.26 no.4
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• pp.589-602
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• 2009

We investigated 'Song of the Sky Pacers, Adopted to the New Methods'(新法步天歌), the latest version of Joseon's 'Song of the Sky Pacers'(步天歌). Due to the influence of new knowledge on Chinese asterisms imported from the Ching dynasty, 'Song of the Sky Pacers with New Star-Charts' was written in the eighteenth century. However, the disagreement between song and star-charts was causing confusion in practical applications such as Joseon's national examination for selecting astronomers. In order to improve this situation, Royal Observatory of the Joseon dynasty (觀象監) published 'Song of the Sky Pacers, Adopted to the New Methods' based upon star-charts and song in the Sequel of I-Hsiang-K'ao-ch'eng (欽定儀象考成續編). The New Song was edited by a middle-class professional astronomer Yi Jun-yang (李俊養), and corrected by a nobleman Nam Byeong-gil (南秉吉). We establish a brief biography of Yi Jun-yang. The New Song preserves the genuine characteristics of previous Joseon's Song including the format of title of each lunar mansion and description on the location of the Milky Way in the asterisms. The description of the Milky Way was newly written based on the data in volume 31 and 32 of the Sequel of I-Hsiang-K'ao-ch'eng.

• Journal of Oral Medicine and Pain
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• v.35 no.1
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• pp.1-18
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• 2010

I'd like to introduce a teaching method to improve learning efficiency. Most students are likely to ignore what they don't understand in the class of a course. The subject of Occlusion is essential to understanding prosthodontic and orthodontic subjects. It is necessary to let students know and review what they don't understand among parts of a chapter in the course of Occlusion. Therefore I look over the examination papers after every examination and input the problems that each student didn't solve into the C-language computer program and print the list of the contents that each student must study particularly. I give the lists to students and let them review and present their own weak parts of a chapter in the course of Occlusion in the next class. This teaching method leads to improvement in learning and is helpful to students as well as lecturers.