• 대한치과보철학회지
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• 제43권1호
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• pp.15-29
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• 2005

Statement of problem. The adjustable dental impression trays were made for being adjusted their width automatically along the width of dental arch. Purpose. The purpose of this study was to investigate the best retentive form of adjustable dental impression tray, and so to make it a more satisfactory product. Material and methods. The eight pairs of adjustable trays were made of ABS(acrylonitrile butadiene styrene) with different distribution of holes and with or without the rim on the border area of them. The experiment was done with the horse-shoe shaped metal plate to pull out the set impression body from the tray, and the tray jig which was made for holding the tray on a lower part of Universal Testing Machine(UTM, Zwick Z020, Zwick Co., Germany). After the impression in the tray was allowed to set four minutes, a tensile force was applied at right angles to the tray which had been previously seated on the jig. The force was applied to measure a maximum retentive force by use of a UTM at a constant strain rate of 100mm per minute. A 2-factor analysis of variance (p<.05) was used to determine whether differences existed among distribution of retentive holes and between rim existing and not. Results. 1 The retentive force of the upper and lower resin tray with 2mm holes on the tray border was highest(25.83/24.98kg). (p<.05) 2. As the tray had more retentive holes, it was less retentive. 3. There was no significant difference in the retentive force of the varied hole intervals in the case of distributing all the area. (p>.05) 4. The rimless trays were more retentive generally, than the rimmed trays except 2 case: upper tray group-all area / 2 mm, intervals and lower tray group-margin only / 2 mm, intervals.(p<.05) 5. Most of the adjustable trays were showed higher retentive force than perforated metal tray except the lower group that perforated on the all area at intervals of 2 mm.

• 한국과학교육학회지
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• 제19권1호
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• pp.62-77
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• 1999

이상화는 물리학 연구뿐 아니라 물리학을 배우는 학습 과정에서도 중요한 역할을 한다. 본 연구에서는 역학과 전기, 그리고 열역학 영역에서 문제 해결 과정과 현상의 설명 과정에는 어떠한 이상 조건이 포함되어 있다고 생각하는지에 대해 일반계 고등학생과 과학고 학생, 그리고 과학 교사를 대상으로 조사하였다. 조사 결과, 과학교육학자들이 예상했던 것과는 달리 많은 학생들이 다양한 종류의 이상 조건들을 잘 언급하였음을 알 수 있었다. 물론, 이상 조건과 일반적 조건을 구분하지 못하거나 현상을 그대로 기술하거나 법칙을 언급하는 것으로 이상 조건을 대신하기도 하였다. 특히, 이상 조건에 대한 생각에서 여러 가지 오개념이 발견되어 이상 조건에 대한 연구와 오개념 연구가 연관성을 가질 수 있음을 발견하였다.

• 한국수학교육학회지시리즈A:수학교육
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• 제27권1호
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• pp.15-23
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• 1988

We are at the onset of a major revolution in education, a revolution unparalleled since the invention of the printing press. The computer will be the instrument of this revolution. Computers and computer application are everywhere these days. Everyone can't avoid the influence of the computer in today's world. The computer is no longer a magical, unfamiliar tool that is used only by researchers or scholars or scientists. The computer helps us do our jobs and even routine tasks more effectively and efficiently. More importantly, it gives us power never before available to solve complex problems. Mathematics instruction in secondary schools is frequently perceived to be more a amendable to the use of computers than are other areas of the school curriculum. This is based on the perception of mathematics as a subject with clearly defined objectives and outcomes that can be reliably measured by devices readily at hand or easily constructed by teachers or researchers. Because of this reason, the first large-scale computerized curriculum projects were in mathematics, and the first educational computer games were mathematics games. And now, the entire mathematics curriculum appears to be the first of the traditional school curriculum areas to be undergoing substantial trasformation because of computers. Recently, many research-Institutes of our country are going to study on computers in orders to use it in mathematics education, but the study is still start ing-step. In order to keep abreast of this trend necessity, and to enhance mathematics teaching/learning which is instructed lecture-based teaching/learning at the present time, this study aims to develop/present practical method of computer-using. This is devided into three methods. 1. Programming teaching/learning method This part is presented the following five types which can teach/learn the mathematical concepts and principle through concise program. (Type 1) Complete a program. (Type 2) Know the given program's content and predict the output. (Type 3) Write a program of the given flow-chart and solve the problem. (Type 4) Make an inference from an error message, find errors and correct them. (Type 5) Investigate complex mathematical fact through program and annotate a program. 2. Problem-solving teaching/learning method solving This part is illustrated how a computer can be used as a tool to help students solve realistic mathematical problems while simultaneously reinforcing their understanding of problem-solving processes. Here, four different problems are presented. For each problem, a four-stage problem-solving model of polya is given: Problem statement, Problem analysis, Computer program, and Looking back/Looking ahead. 3. CAI program teaching/learning method This part is developed/presented courseware of sine theorem section (Mathematics I for high school) in order to avail individualized learning or interactive learning with teacher. (Appendix I, II)

• 영재교육연구
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• 제23권1호
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• pp.67-87
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• 2013

본 연구에서는 고등학교 영재학생들의 학업부정행위에 대한 인식의 개념도를 작성하여 영재학생들의 인식에 관한 개념구조를 제시하고, 영재학생들과 일반학생들의 학업부정행위에 대한 인식차를 비교하였다. 본 연구는 영재의 특성에 대해 파악하고 이를 통하여 영재학생들을 지도하는데 있어서 여태까지 강조되어 왔던 지식 영역뿐만 아니라 도덕성, 인성 등과 같은 정의적 영역에 대한 올바른 접근 및 지도방법을 모색하는 데 그 목적이 있다. 이를 위해 고등학교 영재학생 초점집단 63명의 브레인스토밍으로 얻어진 진술문들을 종합하여 64개의 최종 진술문을 확정하였고, 이들 진술문은 초점집단 63명 중 다시 선발된 13명의 연구 참여자에 의해 분류, 평정되었다. 그 후 다차원 척도분석과 위계적 군집분석을 통해 개념도를 작성한 결과 고등학교 영재학생의 학업부정행위에 관한 인식은 총 5개의 군집으로 분류되었으며, 각각의 군집명은 '용납할 수 없는 친구의 부정행위', '사회적 구조, 영재성, 그리고 부정행위 간의 불가분의 관계', '부정행위 요구로 인한 심적 갈등, 대처 및 용인 수준', '개인 내면의 비도덕성(도덕불감증)', '도덕성과 사회정의에 근거한 판단'으로 나타났다. 또한 영재학생 150명과 일반학생 160명을 대상으로 각 진술문에 대한 동의 정도를 likert 6점 척도로 표시하게 한 후 두 집단 사이의 인식 차를 살펴본 결과 '용납할 수 없는 친구의 부정행위', '도덕성과 사회정의에 근거한 판단' 군집은 두 집단 간의 유의미한 차이가 전무하거나 매우 미미한 반면, '사회적 구조, 영재성, 그리고 부정행위간의 불가분의 관계', '부정행위 요구로 인한 심적 갈등, 대처 및 용인 수준', '개인 내면의 비도덕성(도덕불감증)' 군집은 두 집단 간의 인식 차가 매우 큰 것으로 나타났으며, 전체적으로는 영재학생이 일반학생보다 학업부정행위에 관해 더 도덕적인 입장에서 판단하는 것으로 나타났다. 본 연구의 결과는 영재들의 도덕성과 관련하여 논의되었다.

• 대한치과보철학회지
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• 제39권3호
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• pp.243-249
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• 2001

Statement of the problem. The interest in all-ceramic restorations has increased as more techniques have become available. With the introduction of machinable dental ceramics and CAD/CAM systems or Copy-milling systems there is a need for evaluating the quality levels of these new fabrication techniques. Purpose. This study was to evaluate the fitting accuracy of machined all-ceramic crowns made out of an industrially prefabricated feldspathic porcelain. Material and Methods. Three master models with different cutting depth (0.8mm/1.0mm/1.2mm)were produced using a palladium-silver alloy. A total of 36 working dies, 12 of each form, was used for the modellation of prototype resin copings and 36 additional crowns, 12 of each cutting depth, were produced by using the $CEREC^{(R)}2$ system for all crowns. The maginal fit of all 72 crowns was then evaluated on their respective master die at 54 circularly staggered points of measurement per crown under a fixation pressure of 30 N by using a computerized video image system. Results. The medians of the copy-milled $CELAY^{(R)}$ crowns ranged from 29 to $36{\mu}m$. The highest value for the marginal gap was found in group B (cutting depth 1.0mm) at $107{\mu}m$. The median for the $CEREC^{(R)}2$ crowns was found between 43.5 and $70{\mu}m$. The maximum values for all three groups ranged from $181{\mu}m$ to $286{\mu}m$. With $286{\mu}m$ the highest value for marginal gap was found in group C. the Kruskal-Wallis test and multiple comparisons analysis procedure revealed a significant influence of the production technique on the marginal fit in all three groups (p<0,02). Conclusion. 1. The $CELAY^{(R)}$ system is capable to produce all-ceramic crowns with a significantly better marginal fit than the $CEREC^{(R)}2$ system. 2. As far as premolar crowns produced with the $CEREC^{(R)}2$ system are concerned, the cutting depth has a significant influence on fitting accuracy. 3. The production of crowns with an acceptable marginal fit is possible with both systems. However, adhesive luting is recommended for milled feldspathic porcelain crowns.

• 대한치과보철학회지
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• 제43권2호
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• pp.264-279
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• 2005

Statement of problem. Intraoral corrosion not only affects the esthetic and function of metallic dental restoration, but also has biologic consequences as well. Therefore, corrosion is considered a primary factor when choosing the dental alloy and laboratory technique. Purpose. The objective of this study was to compare the effects of solder and laser weld on corrosion Material and methods. Test specimens were made of 2 types of gold alloys, Co-Cr and Ni-Cr alloy and fabricated 3 methods, respectively: as cast, solder, and laser weld. For the analysis of corroding properties, potentiodynamic polarization test and immersion test conducted. The potentiodynamic polarization scan curve were recorded in 0.9% NaCl solution(pH 7) using Potentiostat/Galyanostat Model 273A. All specimens were exposed to 0.9% NaCl solution(pH 2.3) during 14 days. Elemental release into corrosive solution was measured by atomic emission spectrometry Differences in corrosion potential and mass release were determined using ANOVA. Results and conclusion. Through analyses of the data, following results were obtained. 1. In Pontor MPF and Wiron 99, corrosion potential of the solder group was statistically lower than as cast and laser weld group (p<0.05) , but there was no difference between corrosion potential of solder group and laser weld group in Pontor MPF and no differences between as cast and laser weld group (p>0.05). In Jel-Bios 10 and Wirobond, there was no difference of corrosion potential according to joining methods(p>0.05). 2. In all tested alloys, the amount of released metallic ion was greatest in the solder group(p<0.05). There was no difference between as cast group and laser weld group in Jel-Bios 10 and Wirobond(p>0.05). 3. In scanning electron microscopic examination. except soldered Wiron 99 specimens, it is impossible to discriminate the corrosive property of solder and laser weld. 4. Under the this experimental circumstances, laser weld appears superior to the solder when corrosion is considered.

• The Journal of Advanced Prosthodontics
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• 제1권2호
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• pp.85-90
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• 2009

STATEMENT OF PROBLEM. Over the years, resin-bonded fixed partial dentures (RBFPDs) have gone through substantial development and refinement. Several studies examined the biomechanics of tooth preparation and framework design in relation to the success rate of RBFPDs and considered retention and resistance form essential for increase of clinical retention. However, these criteria required preparations to be more invasive, which violates not only the original intentions of the RBFPD, but may also have an adverse effect on retention due to loss of enamel, an important factor in bonding. PURPOSE. The object of this in vitro study was to compare the dislodgement resistance of the new types of RBFPDs, the conventional three-unit fixed partial denture, and conventional design of RBFPD (Maryland bridge). MATERIAL AND METHODS. Fifty resin mandibular left second premolars and second molars were prepared on dentiforms, according to the RBFPD design. After model fabrication (five group, n = 10), prostheses were fabricated and cemented with zinc phosphate cement. After cementation, the specimens were subjected to tensile loading at a cross head speed of 4 mm/min in a universal testing machine. The separation load was recorded and analyzed statistically using one-way analysis of variance followed by Duncan's multiple range test. RESULTS. Group V, the pin-retained RBFPDs, had the highest mean dislodgement resistance, whereas specimens of group II, the conventional RBFPDs, exhibited a significantly lower mean dislodgement resistance compared to the other 4 groups (P <.05). There were no significant differences between group I, III, and IV in terms of dislodgement resistance (P>.05). Group V had the highest mean MPa (N/$mm^2$) (P <.05). There was no significant difference between groups I, II, III and IV (P > .05). CONCLUSION. Within the limits of the design of this in vitro study, it was concluded that: 1. The modified RBFPDs which utilizes the original tooth undercuts and requires no tooth preparation, compared with the conventional design of RBFPDs, has significantly high dislodgement resistance (P < .05). 2. The modified RBFPDs which utilizes the original tooth undercuts and requires minimal tooth preparation, compared with the conventional FPDs, has significantly no difference in retention and dislodgement resistance)(P>.05). 3. The pin-retained FPDs showed a high dislodgement resistance compared to the conventional three-unit FPDs (P<.05).

• 대한치과보철학회지
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• 제47권4호
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• pp.385-393
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• 2009

연구목적: 임플란트 경부 디자인의 차이가 경부 치밀골의 응력분포에 미치는 영향을 유한요소법을 이용하여 분석하고자 한다. 연구재료 및 방법: 몸체 형상은 유사 (직경 4.3 mm, 길이 10 mm)하나 경부 디자인이 internal형, external형, 및 submerged형으로 다른 3종의 임플란트 시스템 ((주)덴티스, 대구, 대한민국)에 대하여 축대칭 유한요소모델을 사용하여 해석하였다. 악골 폭경은 7 mm로 동일하게 모델링하였고 하중 조건으로는 임플란트 장축에 평행한 수직하중 50 N, 임플란트 장축에 $45^{\circ}$방향으로 작용하는 경사력 50N을 설정하였다. 결과: 해석한 3종의 임플란트 모두 경부 피질골에 응력집중을 발생시켰으며 디자인 차이에 따른 응력 수준의 차이가 관찰되었다. 경부 피질골의 최대 응력은 수직력 조건에서 internal형, submerged형, external형의 순으로 컸으며, 그 값은 각각 2.71, 2.60, 2.48 MPa였다. 경사력 조건에서는 internal형, external형, submerged형의 순으로 컸으며 그 값은 각각 9.30, 9.14, 8.97 MPa였다. 결론: 임플란트 경부 디자인이 주위 치밀골의 응력 분포에 영향을 미칠 수 있지만 그 차이는 크지 않은 것으로 분석되었다.

• 대한치과보철학회지
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• 제45권6호
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• pp.780-786
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• 2007

Statement of problem. The performance and maintenance of implant-supported prostheses are primarily dependent upon load transmission both at the bone-to-implant interface and within the implant-abutment-prosthesis complex. The design of the interface between components has been shown to have a profound influence on the stability of screw joints. Purpose. The Purpose of this study was to compare the strength and the fatigue resistance of 1-piece and 2-piece abutment connected to oral implant, utilizing an internal conical interface. Material and methods. Twenty $Implatium^{(R)}$ tapered implants were embedded to the top of the fixture in acrylic resin blocks. Ten $Combi^{(R)}$(1-piece) and $Dual^{(R)}$(2-piece) abutments of the same dimension were assembled to the implant, respectively. The assembled units were mounted in a testing machine. A load was applied perpendicular to the long axis of the assemblies and the loading points was at the distance of 7mm from the block surface. Half of 1-piece and 2-piece abutment-implant units were tested for the evaluation of the bending strength, and the others were cyclically loaded for the evaluation of the fatigue resistance until plastic deformation occurred. Nonparametric statistical analysis was performed for the results. Results. Mean plastic and maximum bending moment were $1,900{\pm}18Nmm,\;3,609{\pm}106Nmm$ for the 1-piece abutment, and $1,250{\pm}31Nmm,\;2,688{\pm}166Nmm$ for the 2-piece abutment, respectively. Mean cycles and standard deviation when implant-abutment joint showed a first plastic deformation were $238,610{\pm}44,891$. cycles for the 1-piece abutment and $9,476{\pm}3,541$ cycles for the 2-piece abutment. A 1-piece abutment showed significantly higher value than a 2-piece abutment in the first plastic bending moment (p<.05), maximum bending moment (p<.05) and fatigue strength (p<.05). Conclusion. Both 1-piece and 2-piece conical abutment had high strength and fatigue resistance and this suggests long-term durability without mechanical complication. However, the 1-piece conical abutment was more stable than the 2-piece conical abutment in the strength and the fatigue resistance.

• 대한치과보철학회지
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• 제45권3호
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• pp.303-309
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• 2007

Statement of problem. The effect of gold electroforming on gold alloy was not studied. Purpose. This in vitro study investigate the effect of gold electroforming on gold-silver-palladium alloy. Material and methods. Three pieces of gold strips had undergone the electroforming procedures on one side and then half of the side again electroformed. The set mode for this study was program 1 ($200{\mu}m$). And the processing time was 15min (1/20 time to form $200{\mu}m$ coping). The confocal laser scanning microscope (PASCAL 5, Carl Zeiss, Bernried, Germany) was used to measure the thickness of the pure gold layer electroformed on the gold strips. Half of the gold strip was coated two times with electroformed gold, and the other half one time. The data from the cone focal laser system was processed to get the vertical profile of the strips and the difference of the vertical height between the double coated and single coated layer was regarded as the thickness of the gold coating. The layer thickness value to built 3D image of the cone-focal laser was set $0.5{\mu}m$. Next to the measurement of the thickness of the coating, the Vicker's hardness test was done. It was performed on the double coated surface, single coated surface and non-coated surface (back side) three times each. Results. The mean thickness value gained from gold electroforming technique was measured to be $22{\mu}m$ for sample 1, $23{\mu}m$ for sample 2, $21{\mu}m$ for sample 3. In the same condition of time, power and the amount of electrolyte, the data showed no difference between samples. According to the results of variance analysis, the differences among the variations in number of coating were statistically insignificant (p>0.05), meaning that the two times of gold electroforming coating did not change the hardness of gold-silver-palladium alloy. Conclusion. The test of thickness of gold coating proved the coherency of the gold electroforming procedure, in other words, when the power, the exposed surface area, processing time and the amount of electrolytes were set same, the same thickness of gold would be coated on. The hardness test showed that the electroformed gold coating did not change the hardness of the gold-silver-palladium alloy when it is coated not more than $45{\mu}m$.