• Journal of Periodontal and Implant Science
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• v.32 no.2
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• pp.371-378
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• 2002

In this study, 40 hypersensitive teeth of 19 patients were investigated. The procedures performed were as follows: Before desensitization, EPT at occlusal third of buccal surface was done for the evaluation of pulp vitality and the EPT value was recorded for the reference value. And mechanical and thermal test was executed for the test of hypersensitivity. If the tooth responded to the above tests, we did EPT at the exposed surface, using toothpaste as a electrolite medium and recorded the EPT value at patient's response. After the tests had been done, desensitization procedures with Gluma(R) Desensitizer were performed according to the manufacturer's instructions. After desensitization, the same tests except EPT at occlusal third were repeated. All the 40 teeth responded positive before desensitization and negative after desensitization procedures. The EPT value at occlusal third ranged from 31 to 65 (48.9${\pm}$7.2). Before desensitization 34 teeth responded at EPT value of 2 and the remaining 6 teeth was in the range of 17 to 25. After desensitization all 40 teeth responded from 12 to 27 (19.6${\pm}$3.5). The 6 teeth responded at greater number than 2 before desensitization was in the range of 18 to 23. Within the limitations of this study we can conclude that: When a tooth with dentinal hypersensitivity responds to mechanical and thermal stimulation, the tooth shows very low resistance to electricity at the exposed surface while when a tooth is desensitized and doesn't show respond to mechanical and thermal stimuli, the tooth shows increased level of resistance to electric stimulation at the exposed surface. EPT can be used for the diagnosis of dentinal hypersensitivity. Furthermore EPT will be useful to evaluate the outcome of desensitization procedures. However, EPT is not a valid tool for measuring dentinal hypersensitivity.

• Applied Chemistry for Engineering
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• v.27 no.6
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• pp.583-589
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• 2016

Lubricant additives including zinc dialkyldithiophosphate (ZDDP) containing metal have been widely used due to the advantage of very low cost, but they can generate impurities such as ash. In this work, ZDDP containing metals was partially replaced with bis[3-(dialkyloxyphosphorothionyl) thio-2-methylpropanyloxy] butane (BAP4s) which was synthesized conveniently and effectively from alkanediol without any metal components. Also, the wear resistance property of synthesized BAP4s were studied. Wear scar diameter (WSD) values of BAP4s with butyl, octyl, decyl, dodecyl or tetradecyl groups were also measured by four-ball test. As the length of the alkyl group increased from 4 to 8, the WSD value of BAP4s decreased rapidly from 0.59 to 0.45 mm, but from 8 to 14, the value increased very slowly from 0.45 to 0.50 mm. Thus, among all BAP4s, B8P4 having BAP4 with the octyl group, showed the lowest WSD value. Furthermore, the WSD values were measured in a lubricant base oil mixed with a 0.50 percent concentration (w/w) of either BAP4 or ZDDP. The former was 0.55 mm, and the latter was 0.45 mm. The thermal stability and tribofilm formation peroperty were also measured by thermogravimetric analyzer (TGA) and energy-dispersive X-rays spectroscopy (EDS), respectively.

• Journal of the Korean Applied Science and Technology
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• v.31 no.4
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• pp.679-687
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• 2014

In this study, a new paint which is able to resist the cavitation erosion is tried to be developed by using urethane added with nano particles such as multi-wall and single-wall carbon nano tube and spherical and fiber type graphite. The new paint synthesized was characterized with physical properties and resistivity to cavitation erosion($t_{50}$). Among nano particles, fiber type graphite($t_{50}$ 292min) showed high hardness and wear resistance compared with spherical type($t_{50}$ 182min). For carbon nano tube, single-wall type($t_{50}$ 286min) was higher than multi-wall type in wear resistance. Fiber-type graphite was the best nano-particle for paint with resistivity to cavitation erosion. In the application test of paint, the manually painted sample showed surface with smooth but the surface of sample prepared with spray was not smooth. During spray, dust was fixed on the surface.

• 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.

• The Journal of Korean Academy of Prosthodontics
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• v.57 no.2
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• pp.182-188
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• 2019

A proper vertical dimension and a harmonious occlusal plane are essential to satisfy a patient esthetically and functionally. A maxillomandibular occlusal vertical dimension is determined by the elevators which repeatedly contracts to a certain length, and a tooth location is determined by a maxillomandibular vertical dimension. The patient of this case came in with the incongruity of the lips and the occlusal plane. The result of clinical test showed the lack of length of the lower anterior due to the reduction of vertical dimension, the deep overbite of anterior, the excessive attrition of anterior, and the incongruity of occlusal plane. After the diagnostic wax-up, the temporary restoration was installed, and final prosthesis was installed after 6 months. As a result, the patient obtained a functionally and esthetically satisfying result.

• Journal of the Korean Applied Science and Technology
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• v.31 no.1
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• pp.74-82
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• 2014

For this research, prepared ammonium dihydrogen phosphate aqueous solution and polyurethane dispersion. Use these resin, this article has been analyzed about change of mechanical properties by increasing amount of ammonium dihydrogen phosphate aqueous solution in polyurethan resin on coated leather and dried film. According to measure data for solvent resistance, DPU(polyurethane dispersion) resin and DPU-AD1, D2, D3(samples of polyurethaneresin with ammonium dihydrogen phosphate aqueous solution) had good property. As known in the results, increase of ammonium dihydrogen phosphate constant did not influence to big change of polyurethane resin properties. As test of tensile strength, DPU had highest tensile characteristic($3.114kg_f/mm^2$) and DPU-AD3 had lowest tensile characteristic($2.510kg_f/mm^2$). As same as tensile characteristic, abrasion test determined DPU(50.5 mg.loss) had highest properties. In elongation case, DPU had best properties(602 %) in this experiment.

• Elastomers and Composites
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• v.48 no.3
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• pp.201-208
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• 2013

In this study, effect of different amounts of sulfur and vulcanization accelerators in the acrylonitrile styrene-butadiene rubber (AN-SBR)/silica compounds on the properties of tire tread compound were studied. As a result, cure rate and degree of cross-linking of the compounds were increased due to enhanced cross-linking reactivity by the increased amounts of sulfur and vulcanization accelerators. Also, abrasion resistance and the mechanical properties such as hardness and modulus of the compounds were improved by enhanced degree of cross-linking of the compounds. For the dynamic properties, tan ${\delta}$ value at $0^{\circ}C$ was increased due to the increase of glass transition temperature ($T_g$) by enhanced degree of cross-linking of the compound, and tan ${\delta}$ value at $60^{\circ}C$ was decreased. Initial cure time ($t_1$) showed the linear relationship with tan ${\delta}$ value at $60^{\circ}C$. This result is attributed that reduced initial cure time ($t_1$) of compounds by applying increased amount of curatives can form cross-linking in early stage of vulcanization that may suppress development of filler network. This result is verified by observation on the surface of annealed compounds using AFM (atomic force microscopy). Consequently, decreased initial cure time is considered a very important parameter to reduce tan ${\delta}$ at $60^{\circ}C$ through reduced re-agglomeration of silica particles.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1998.11a
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• pp.72-72
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• 1998

원자력발전소 1차계통내 밸브의 경면처리(hardfa따1잉에 사용되는 재료는 $90~343^{\circ}C$의 고온과 높은 접촉응력 그리고 급격한 압력변화가 일어나는 환경에서 사용되기 때문에 내마모성과 내식성 그리고 cavitation erosion 저항성이 우수한 Co계 Stellite 합금이 현재 사용되어진다. 그러나 Co가 원력발전소 1차계통의 방사선장을 형성하는 주요 원소로 알려지면서 S Stellite 합금을 대체할 수 있는 Fe계 경면처리용 합금을 개발하려는 연구가 진행되고 있다. 현재 Fe계 경면처리용 합금의 개발은 적절환 팝금원소를 첨가하여 적충결함에너지를 낮춤 으로써 전위의 교차슬립을 억제하여 표면을 경화시키고, 소성변형을 억제하여 마모저항성을 향상시키려는 방법으로 연구가 진행되고 있다. 본 연구에서는 Fe-Cr-Ni-Si-C 합금에 Fe계 합금의 적충결함에너지를 감소시키는 것으로 알려진 vanadium을 0, 1, 2wt%첨가하여 첨가량의 변화가 cavitation erosion 저항성에 미치 는 영향을 조사하였다. Cavitation erosion 실험은 초음파를 이용하여 미세한 기포를 발생시키는 vibratory type으로 A ASTM G-32 규격에 따라 제작된 실험장치를 이용하여 $25{\pm}2^{\circ}C$의 온도의 증류수 속에 잠긴 상태에서 실시하였다. 시면은 지름 16mm, 두게 7mm의 버턴형태로 vanadium 첨가량을 변화시킨 조성을 아크 용융 방법을 이용하여 제작하였으며 hom끝단부에 부착하여 cavitation e erosion 저항성 살험을 하였다. 시편의 cavitation erosion 실험시간에 따른 무게감소량을 측 정하였으며 cavitation erosion 시킨 시편의 표면을 SEM으로 관찰하였다.겨지는 열전달 매체액 과 신규 부식억제제가 적용된 시스템 등 객관적으로 확인된 부식억제제 시스랩에 대 하여 다양한 평가 방법을 동원 비교분석하고자 하였다. 실험은 KSM 2142에 의한 무게감량법, 분극곡선 측정에 의한 $E_P$(공식개시전위), $E_R$(재부동태화전위) 측정, 시간에 따른 자연전위 변화 측정 빛 이때의 부식속도(선형분극법), 인위적인 피막 파괴 전,후 의 전위 변화 및 부식속도 측정법에 의한 국부부식 발달 저지능 등을 평가하여 각 실험결과를 비교분석하여 보았다. 수록 민감하여 304 의 IGSCC 와 매우 유사한 거동을 보인다. 본 강연에서는 304 와 600 의 고온 물에서 일어나는 IGSCC 민감도에 미치는 환경, 예민화처리, 합금원소의 영향을 고찰하고 이에 대한 최근의 연구 동향과 방식 방법을 다룬다.다.의 목적과 지식)보다 미학적 경험에 주는 영향이 큰 것으로 나타났으며, 모든 사람들에게 비슷한 미학적 경험을 발생시키는 것 이 밝혀졌다. 다시 말하면 모든 사람들은 그들의 문화적인 국적과 사회적 인 직업의 차이, 목적의 차이, 또한 환경의 의미의 차이에 상관없이 아름다 운 경관(High-beauty landscape)을 주거지나 나들이 장소로서 선호했으며, 아름답다고 평가했다. 반면에, 사람들이 갖고 있는 문화의 차이, 직업의 차 이, 목적의 차이, 그리고 환경의 의미의 차이에 따라 경관의 미학적 평가가 달라진 것으로 나타났다.corner$적 의도에 의한 경관구성의 일면을 확인할수 있지만 엄밀히 생각하여 보면 이러한 예의 경우도 최락의 총체적인 외형은 마찬가지로 $\ulcorner$순응$\lrcorner$의 범위를 벗어나지 않는다. 그렇기 때문에도 $\ulcorner$

• The korean journal of orthodontics
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• v.29 no.2 s.73
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• pp.219-237
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• 1999

This study was designed to evaluate the frequency and the severity of root resorption of the permanent teeth before orthodontic treatment by means of radiograph in the malocclusion patients. In this study the author analysed the frequency and the severity of root resorption in individual teeth, the relationships of the frequency and the severity of root resorption and age, sex, Angle's classification, overjet, overbite, and maxillary and mandibular incisor inclination, and the relationships of the frequency of root resorption and the characteristics of malocclusion and marked occlusal attrition showed in individual teeth. The results were as follows. 1. All of the persons examined showed some evidence of root resorption in one or more of the permanent teeth, $35.84\%$ of the teeth examined and more frequent in female group than male group(p<0.01). 2. On the susceptibility of the root resorption in individual teeth in this study, the author found the mandibular incisors and the maxillary incisors, in the order named, to be most susceptible in all affected teeth, but maxillary central incisors, maxillary first bicuspids, and maxillary lateral incisors, in the order named, were more susceptible to marked root resolution. 3. The more proclined maxillary Incisors the more affected root resorption in four maxillary incisors and the more proclined mandibular incisors the more affected root resorption in four mandibular incisors. 4. Overbite more affected root resorption than overjet, and the higher tender to openbite the more frequent was root resorption. 5. On the characteristics of malocclusion showed in individual teeth, the openbite teeth combined with crossbite, were most frequent in root resolution.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.6
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• pp.468-472
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• 2005

In order to prevent adhering of molten glass on a mold wall, the wall is swabbed with lubricant oil before forming. However, the swabbing process can be removed from the entire processes of the glass forming if the mold wall is made of a porous sintered material. The purpose of the present study is to manufacture a sintered material(having a sintered density of $85{\~}90\%$)which is the most appropriate into. plane material for a glass mold. For the research, SUS310L-based coarse powder (${\~}150{\mu}m$) and SUS420J2-based fine powder ($40{\~}50{\mu}m$) were used for the compact materials, and effects of compaction pressure and sintering condition(atmosphere, temperature) were investigated. The results obtained were as fellows. (1) By means of solid phase sintering, a desired sintering density could not be achieved in any case when using a 310L-based powder having a large particle size. (2) When sintering green compacts(compaction pressure of $2ton/cm^2$) in a commercial vacuum furnace(at $1300^{\circ}C$ for 2 hours), the sintered compacts had densities of $6.2g/cm^3(79\%)$ for 310L + 0.03$\%$B, $6.6g/cm^3 (86\%)$ for 420J2, $7.3g/cm^3(95\%)$ for 420J2+(0.03)$\%$B, and $7.6g/cm^3(99\%)$ for 420j2+(0.06)$\%$B, respectively. As a result, it is regarded that sintered compacts having a desired porosity may be achieved by vacuum sintering the 420J2-based powder (low pressure compaction) and the 310L+0.03$\%$B-based powder (high pressure compaction).