• Restorative Dentistry and Endodontics
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• 제18권2호
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• pp.277-290
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• 1993

Dental caries is considered to be caused by demineralization by organic acid produced by microorganism. But the formation of subsurface lesion in initial caries make it diffcult to explain by simple demineralization. This study is carried out on the basis of thermodynamic concept proposed by Margolis and Moreno. The purpose of this study is to evaluate the effects of acid concentration and pH of lactate buffer system on the artificial caries lesion progress. 160 teeth without any crack, defect or opaque enamel were used and coated with nail varnish except the window ($2{\times}3$ mm). Under the constant degree of saturation(D.S.). The teeth were divided into 8 groups according to acid concentration(10mM, 25mM, 50mM, 100mM) and pH(4.3, 5.0, 6.0). Each group was immersed in buffer solution for 3, 6, 9, 18 days under controlled temperature($25^{\circ}C$). After cutting through the window and grinding, the specimens, 100-150 um in thickness, were imbibed in water or air and examined using polarilizing microscope. The depth of the surface and subsurface surface lesion were measured. 1. In the constant pH and D. S. value, the subsurface lesion progresses more rapidly as the concentration of lactic acid increases. (0.01, 0.025, 0.05, 0.1) 2. In the constant acid concentration and DS value, the subsurface lesion progresses more slowly as the pH increases. (4.3, 5.0, 5.5, 6.0) 3. The width of surface lesion seems to be constant independant of pH and acid concentration.

• Restorative Dentistry and Endodontics
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• 제14권2호
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• pp.5-19
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• 1989

The purpose of this study was to observe the microleakage of composite resin filling using several glass ionomer cements. The Class V cavities of eighty noncarious human molars were prepared at the cementoenamel juction on the facial and lingual surfaces of each tooth with a No.330 carbide bur in a high speed handpiece. The cavity dimensions were $3.0{\pm}0.5mm$ wide, $2.0{\pm}0.5mm$ high, and $1.5{\pm}0.5mm$ deep and all enamel cavosurface margins were beveled with a No.558 carbide bur in low speed handpiece. The bevel was approximately $45^{\circ}$ and 0.5-1.0mm in width. A total of the 160 cavities was divided into four groups, and then 144 cavities among them were three experimental groups and remaining sixteen cavities were control group. All of the prepared cavities were restored as follows: group 1 : Preparations were restored with there three glass ionomer cements. group 2 : Preparations were restored with a composite resin with three glass ionomer cement bases placed $0.2{\pm}0.1mm$ short of the cavosurface margin. group 3 : Preparations were restored with a composite resin with three glass ionomer cement bases extened to the cavosurface margin. group 4 : As control group, preparations were restored with a composite resin, PALFIQUE. The specimens were then thermocycled in a range of $6^{\circ}C-60^{\circ}C$ and immersed in a bath of 2.0% aqueous basic fuchsin solution for 24 hours. Dye penetration was read on a scale of 0 to 4 by Tani and Buonocore's method. The following conclusions were derived from the results obtained; 1. All groups showed significantly more leakage at the gingival margins than at the occlusal margins(p<0.0005). 2. At the gingival margins, group 1 showed less leakage than group 3(p<0.01) and group 4(p<0.0005), while group 3 exhibited less leakage than group 2(p<0.01) and group 4(p<0.0005). 3. At the occlusal margins, group 4 showed less leakage than group 3(p<0.1) and group 1(p<0.005), while group 3 exhibited less leakage than group 2(p>0.1) and group 1(p<0.025).

• 보건교육건강증진학회지
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• 제14권2호
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• pp.149-158
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• 1997

This research reached conclusions to prepare indications for activity of Oral health Instruction of the first grade in an elementary school by several items of Oral examination and investigation. 1. The frequency of brushing their teeth of the children that were examined was generally two times a day(64.42%) : it showed that it was the highest after breakfast (30.08%), and hardly any brushed their teeth after lunch(6.36%). 2. Most of the toothbrushes used were for children(97.46%), and the proper time to change their toothbrushes was less than two months(65.25%), but 31.37% of them used their toothbrushes for more than three mouths. 3. They usually used toothpaste. Those using toothpaste were 64.41%. By the way, for adults was the percentage 31.36%, and for those including fluorine it was 74.58%. 4. They mainly ate cookies, beverages, (coke, cider, etc.), fruit, bread, milk and so on for their dessert. 5. Most students had dental plaque (95.76%) : 14.4% of then had calculus and 23.73% had gingivitis. 6. The results of disclosing showed that twelve anterior teeth were colored. The Mandible was comparatively more severe than the Maxillary in the colored -degree. the low -right - laterial incisor was the most severe and the right central incisor was the most severe of the Maxillary. 7. The pressure of tooth - brushing showed that half of the students brushed their teeth severely. The width of the brushing movemtnts was more than 8mm for 51.70%, 5-8mm for 33.05% and less than 5mm for 15.25% Therefore 66.5% of them were shown to move their brushes insufficiently or oppositely. 8. When they brushed, the children who opened their mouth while brushing were more than those who kept their mouth closed.

• Journal of Periodontal and Implant Science
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• 제27권1호
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• pp.179-189
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• 1997

Teeth mobility is an important part of a periodontal examination, because it represents a function of the persisting height of the alveolar bone and the width of the periodontal ligament. The purpose of this study was to evaluate clinical difference in teeth mobility after treatment with the modified Widman flap and the undisplaced flap in humans. Twenty males with moderate periodontal disease were selected. The severity of periodontal disease was evaluated with sulcular bleeding index, pocket depth and attachment level and tooth mobility was measured with Periotest(Siemens Co., Germany) at the initial examination, 1, 2, 4, 6, 8 and 12 weeks following the modified Widman flap and the undisplaced flap operation using the split-mouth technique. The relation of mobility to clinical parameters was statistically analyzed by multiple regression and the change of teeth mobility according to healing process by independent t-test using SPSS program. The results were as follows: 1. There was a strong relationship between the Periotest value(PTV) and attachment level. 2. The change of teeth mobility in both flap procedures was increased significantly at 1 week post-op. and was decreased to preoperative level at 4 weeks post-op, in modified Widman flap and at 6 weeks post-op. in undisplaced flap. 3. The change of teeth mobility in premolar teeth group in undisplaced flap compared to modified Widman flap was generally increased but these changes were not statistically significant. The changes of teeth mobility in molar teeth group in undisplaced flap was increased significantly at 2 weeks post-op.. 4. The change of teeth mobility following undisplaced flap was increased significantly compared to that of modified Widman flap at 2 weeks post-op.

• Restorative Dentistry and Endodontics
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• 제22권2호
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• pp.519-535
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• 1997

The responses of human pulp fibroblastic cells to Ga-As Semi-Conductor-Dens-Bio Laser (Frequency: 5 Hz~10,000 Hz Model: SD-101A RCA, U.SA)) were examined in vitro using pulp fibroblastic cells obtained from the pulp tissue of human tooth. The mitogenic effect of soft laser was assessed by measuring the MTT assay. The morphologic effect for soft laser showed under the scanning and transmission electron microscopy. The results as follows; 1. The mitogenic response of the soft laser was not observed until 4th time of radiation, while the mitogenic response at 4th time increased mitogenic effect by as much as 1.7 fold compared to the control value. 2. The mitogenic response of the soft laser on pulp fibroblast differ from the mitogenic response on other fibroblasts. 3. In scanning electron microscopic study, The microvilli of cell surface increased gradually with width and length after laser radiation, it demonstrate that development of microvilli have close connection with differentiation of cells. 4. Under the transmission electron microscope, The laser-treated cells maintained their elongated shape and a high degree of cellular polarization. The large cell body containing a well developed Golgi complex, a large number of profiles of rough endoplasmic reticulum, and great numbers of mitochondria. 5. The laser-treated cells maintained the long straight bundles of closely apposed microfilaments or individual filaments forming a cross-linked network. These findings suggest that the laser may have important roles in promotion of pulp healing and consequently may be useful for clinical application in pulp regenerative procedures.

• 대한치과교정학회지
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• 제24권2호
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• pp.247-273
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• 1994

The purpose of this study was to evaluate the dental arch morphology and the occlusal characteristics in the Koreans from the dental-anthropological point of view. The sample consisted of dental stone casts obtained from 120 Korean adults and 142 Japanese adults. Japanese casts and Caucasian data had been preserved at the Dept, of Orthodontics of Tokyo Medical and Dental University. Tooth size and dental arch morphology of the Koreans were compared with that of the Japanese. On the other hand, the variations of 30 crown traits, categorized and quantitatively graded, were compared between two peoples and the frequency distribution of each crown traits were analyzed by means of Chi-square test. The results were summerized as followings ; 1. There was a significant sexual difference in dental arch length and width in the Korean, in which male had a longer and wider dental arch than female. There was a close resemblance for dental arch morphology between the Koreans and the Japanese, except for a little longer mandibular arch of the Japanese. 2. In general, Korean male had wider crown than female, particulary in central incisor,canine,1st molar of maxilla and canine, 1st and 2nd molar of mandible with significance. The Korean had wider maxillary first molar, smaller mandibular first and second molar than the Japanese in both sex. 3. In crown traits of the Korean, shovel-shaped incisor showed lower frequency distribution than in the Japanese, but higher than in the Caucasians. Frequency of incisor reduction was shown higher distribution than in the Japanese and the Caucasians. Carabelli's tubercle showed higher frequency distribution than in Japanese, but remarkably lower than in Caucasians.

• 전기전자학회논문지
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• 제14권2호
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• pp.90-97
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• 2010

본 논문에서는 DT-CMOS(Dynamic Threshold voltage CMOS) 스위칭 소자와 DTMOS Error Amplifier를 사용한 고 효율 전원 제어 장치(PMIC)를 제안하였다. 높은 출력 전류에서 고 전력 효율을 얻기 위하여 PWM(Pulse Width Modulation) 제어 방식을 사용하여 PMIC를 구현하였으며, 낮은 온 저항을 갖는 DT-CMOS를 설계하여 도통 손실을 감소시켰다. 벅 컨버터(Buck converter) 제어 회로는 PWM 제어회로로 되어 있으며, 삼각파 발생기, 밴드갭 기준 전압 회로, DT-CMOS 오차 증폭기, 비교기가 하나의 블록으로 구성되어 있다. 제안된 DT-CMOS 오차증폭기는 72dB DC gain과 83.5위상 여유를 갖도록 설계하였다. DTMOS를 사용한 오차증폭기는 CMOS를 사용한 오차증폭기 보다 약 30%정도 파워 소비 감소를 보였다. Voltage-mode PWM 제어 회로와 낮은 온 저항을 스위칭 소자로 사용하여 구현한 DC-DC converter는 100mA 출력 전류에서 95%의 효율을 구현하였으며, 1mA이하의 대기모드에서도 높은 효율을 구현하기 위하여 LDO를 설계하였다.

• 농업과학연구
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• 제47권2호
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• pp.327-335
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• 2020

The purpose of this study was to analyze the load distribution and contact safety factor for the power take off (PTO) gear of a 71 kW class agricultural tractor. In this study, a simulation model of the PTO gear-train was developed using Romax DESGINER. The face load factor and contact safety factor were calculated using ISO 6336:2006. The simulation time was set at 2,736 hours considering the lifetime of the tractor, and the simulation was performed for each PTO gear stage at the engine rated power conditions. As a result of the simulation, the face load factors for the driving gear at the PTO 1^st, 2^nd and 3^rd stages were 1.644, 1.632, and 1.341, respectively. The contact safety factors for the driving gear at the PTO 1^st, 2^nd and 3^rd stages were 1.185, 1.216, and 1.458, respectively. As the PTO gear stage was increased, the face load factor decreased, and the contact safety factor increased. The load distributions for all the PTO gears were concentrated to the right of the tooth width. This causes stress concentrations and shortens the lifespan of the gears. Therefore, it is necessary to improve the face load factor and the contact safety factor with macro-geometry and micro-geometry.

• The Journal of Advanced Prosthodontics
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• 제5권2호
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• pp.187-197
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• 2013

PURPOSE. The purpose of this study was to evaluate various core designs on stress distribution within zirconia crowns. MATERIALS AND METHODS. Three-dimensional finite element models, representing mandibular molars, comprising a prepared tooth, cement layer, zirconia core, and veneer porcelain were designed by computer software. The shoulder (1 mm in width) variations in core were incremental increases of 1 mm, 2 mm and 3 mm in proximal and lingual height, and buccal height respectively. To simulate masticatory force, loads of 280 N were applied from three directions (vertical, at a $45^{\circ}$ angle, and horizontal). To simulate maximum bite force, a load of 700 N was applied vertically to the crowns. Maximum principal stress (MPS) was determined for each model, loading condition, and position. RESULTS. In the maximum bite force simulation test, the MPSs on all crowns observed around the shoulder region and loading points. The compressive stresses were located in the shoulder region of the veneer-zirconia interface and at the occlusal region. In the test simulating masticatory force, the MPS was concentrated around the loading points, and the compressive stresses were located at the 3 mm height lingual shoulder region, when the load was applied horizontally. MPS increased in the shoulder region as the shoulder height increased. CONCLUSION. This study suggested that reinforced shoulder play an essential role in the success of the zirconia restoration, and veneer fracture due to occlusal loading can be prevented by proper core design, such as shoulder.

• 한국산업융합학회 논문집
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• 제23권4_2호
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• pp.701-708
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• 2020

In this paper, we analyzed the optical properties of the LED module for dental care, which has the effect of promoting cell regeneration and scar treatment. The LED module is a U-shaped module suitable for the shape of teeth. It is manufactured with an LED module (632 nm) and an LED module (632 nm + 870 nm), analyzes the results of optical properties, sets the irradiation distance, irradiation time, and is effective in healing skin wounds. Evaluation was conducted. It was tested in 6 test groups according to the light irradiation conditions, and light was irradiated to the scar site every other day for 7 days, 1 day and 3 days. As a result, it was confirmed that the effect of scar treatment was the highest when the combined wavelength of 632 nm + 870 nm was irradiated in pulse mode than when the single wavelength was irradiated and the composite wavelength was continuously irradiated. In group C group irradiated with PW Mode: pulse mode (period 36 ms, pulse width 35 ms) using a composite wavelength with LED module (632 nm + 870 nm) than group A without light irradiation, the length of scar reduction was 19 %, the area of the scar was further reduced by 10%, and it was confirmed that it is effective in treating scars in the wound area.