• Restorative Dentistry and Endodontics
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• v.22 no.1
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• pp.358-373
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• 1997

Resin modified glass ionomers were introduced in 1988 to overcome the problems of moisture sensitivity and low early mechanical strength of conventional glass ionomers and to maintain their clinical advantages. The purpose of this study was to evaluate the color stability of four resin modified glass ionomers(Fuji II LC, Vitremer, Dyract and VariGlass), one resin composite material(Z-100), and one conventional glass ionomer(GC Fuji II) under several conditions. These conditions were as follows: 1) before curing, 2) after curing, 3) after polishing, 4) after 500 thermocycling, 5) after 1,000 thermocycling, 6) after 1,500 thermocycling and 7) after 2,000 thermocycling. Three specimens of each material/shade combination were made. Materials were condensed into metal mold with a diameter of 10 mm and a thickness of 2.0 mm, and were pressed between glass plates. The material was polymerized using a light polymerizing unit(Visilux II, 3M, USA). After removal of excess, the surface was polished sequentially on wet sandpapers. A reflection spectrophotometer(Model TC-6FX, Tokyo Denshoku Co., Japan) was used to determine CIELAB coordinates($L^*,a^*$ and $b^*$) of each specimen. CIE standard illumination C was used as the light source. The results were as follows : 1. In comparing different shades of same material, CIELAB color difference(${\Delta}E^*$) value was not significantly different from each other(p>0.05). 2. CIELAB color difference(${\Delta}E^*$) values between after-curing and after-polishing were ranged from 5.53 to 27.08. These values were higher than those of other condition combinations. 3. CIELAB color difference(${\Delta}E^*$) values between before-thermocycling and after-thermocycling were ranged from 1.40 to 7.81. Despite the number of thermocycling increased, CIELAB color difference(${\Delta}E^*$) value was low. 4. The color stability of resin modified glass ionomers was more stable than that of conventional glass ionomers but less stable than that of Z100.

• Restorative Dentistry and Endodontics
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• v.30 no.3
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• pp.170-177
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• 2005

This study was conducted in order to assess whether the form of the shade guide affects in deciding the color of the teeth using the shade guide Eight shade light cured composite resins (Esthet-X, Dentsply, Milford, USA) were used in this study. Shade guides including the model of maxillary central incisors, teeth-form shade guide, doughnut form shade guide, and shade guide with perforated gray shield were prepared with eight shade composite resins and provided the codes randomly After arranging the models of teeth, 19 dentists working at the clinic of the Dentistry of Chonnam University Hospital and 65 students of college of dentistry, Chonnnam University selected the shade guides corresponding to the color of each tooth on the gray board under the D$_{65}$ standard illuminant. Bl shade showed highest accuracy of about 95% among all shade guides of 3 forms applied to the test and regardless of observer, tooth form shade guide showed the highest accuracy (p < 0.05) , and the doughnut form showed the lowest accuracy (p < 0.05). At the time of deciding on the color of the teeth using the shade guides as a result of above, the forms of the shade guides can affect the accuracy, and it suggests that the development of the diversified forms of shade guides, which may obtain more accurate results, is required.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.29 no.6
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• pp.397-406
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• 2003

The purpose of this study was to observe the titanium implant osseointegration in the osteoporosis-induced animal model. Seventy rats, 11 weeks of age, were divided into two groups : an ovariectomized group and a control group. Titanium screw implants(diameter, 2.0mm; length, 3.5mm) were placed into left tibias of 70 rats, 35 in the control group and 35 in the experimental group. The rats were sacrificed at different time interval (1, 2, 3, 4, 6, 8, and 12 weeks after implantation) for histopathologic observation, histomorphometric analysis and immunohistochemistry with fibronectin and CD34 antibody. The results obtained from this study were as follows: 1. Histopathologically findings, newly formed bone was seen at 3 weeks and became lamellar bone at 8 weeks, and mature trabecullar bone was seen at 12 weeks control group. In experimental group, thickness of regenerated bone increased till 8 weeks gradually and mature trabecullar bone was seen at 12 weeks. 2. By histomorphometric analysis, marrow bone density and contact ratio of marrow bone to implant decreased significantly from 8 to 12 weeks in experimental group compared to control group and also total bone to implant contact ratio decreased significantly from 8 to 12 weeks in experimental group. 3. Fibronectin immunoreactivity was strong at 3 weeks control group and reduced after 8weeks gradually. But it was continuously strong from 3 to 8 weeks in experimental group. 4. CD34 immunoreactivity was very strong in the newly formed osteoblasts from 3 to 8 weeks control group. But it reacted minimally later. While in experimental group, it reacted continuously strong from 3 to 12 weeks. The results of this study suggest that osteoporosis is not an absolute contraindication to dental implantation if sufficient period suggested after fixture installation till second stage surgery.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.33 no.2
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• pp.131-138
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• 2007

The purpose of this study was to observe the effect of calcium and vitamin D to the titanium implant osseointegration in animal model. 32 rats, 10 weeks of age, were divided into two group: additional calcium and vitamin D supplementation group and a control group. Titanium screw implant(diameter, 2.0mm; length, 3.5mm; pitch-height 0.4mm) were placed into tibia of 32 rats, 16 in the control group and 16 in the experimental group. The rats were sacrificed at different time interval(1, 2, 4, and 8 weeks after implantation) for histopathologic observation, histomorphometric analysis and immunohistochemistry with osteocalcin and osteopontin antibody. Histopathologically findings, newly formed bone was seen at 1 weeks and became lamellar bone at 2 weeks, and mature trabecullar bone was seen at 4 weeks experimental group. In control group, thickness of regenerated bone increased till 4 weeks gradually and trabecullar bone was seen at 8 weeks. By histomorphometric analysis, bone marrow density was increased significantly at 1 and 2 weeks in experimental group compared to control group. Osteocalcin immunoreactivity was strong at 1 week experimental group and reduced after 4 weeks gradually. But it was continuously weakly from 1 to 4 weeks in control group. Osteopontin immunoreactivity was very strong in newly formed bone from 2 to 8 weeks experimental group. And the amount of osteopontin expression was more abundant in experimental group. The results of this study suggest that calcium and vitamin D supplementation promotes bone healing around dental implants

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.2
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• pp.172-183
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• 2002

This study is going to compare the degree of color change which occurs in the following two cases of the factors which cause the color change of extra-staining, one is during glazing by the dental technician, the other is tooth brush abrasion which makes the biggest influence on color change. To compare the degree of color change before and after glazing, a sample was made with vintage incisal porcelain No. 59 OPAL(Shofu Inc, Japan), after that it was painted with three colors of porcelain stainers, then the degree of color was measured with a spectrophometer(Model Chromaview 300, Spectoron Tech Co. Korea) after it had been treated with firing only and glazing after firing 40,000-cycle and 80,000-cycle of tooth brush abrasion test were carried out in order to simulate the brushing effect of 4 years and 8 years by using the abrasion tester. The colors were measured before the test, and after the 40,000-cycle and 80.000-cycle operations and the surfaces were examined by SEM. The results of this study were as follows ; 1. The color change before and after glazing was not great enough to have a clinical significance but the orange color was changed more significantly statistically than the blue and light brown(p<0.05). 2. In the case of the color change of stained porcelain by tooth brushing, carrying out staining and glazing with two-times firings resulted in statically less color change than one firing only(p<0.05). 3. In the case of the difference in the stainer's color, the orange color which has higher chroma was statically more sensitive than the blue color(p<0.05) 4. In the case of the color change after the 80,000-cycle abrasion, all showed color change when there was one firing and the orange stainer showed some color change with clinical significance when firings were done two times.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.2
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• pp.127-138
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• 2012

This study is to assess the effect of preload level on the stress development at the marginal cortical bone surrounding implant neck. A finite element model was created for a single implant placed in the lower jaw bone. An external load of 100N was applied on the top of abutment at 30 degree with the implant axis in lingo-buccal direction. Five different preloads, i.e. 0, 200, 400, 600, 800N were applied to the abutment stem to investigate if and/or how the preload affects on the marginal bone stress. Differences in the marginal bone stress were recorded depending on the level of preload. On the other hand, the tensile stress on the marginal cortical bone decreased in models of higher preload. Preloads between abutment/fixture can increase compressive stresses in the marginal cortical bone although the amount may be insignificant as compared to those generated by functional forces.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.2
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• pp.205-220
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• 2010

Purpose : To analyze the effect of implant designs on insertion torque and stress by performing a comparative study on von Mises stress, torque and normal force through a three-dimensional finite element analysis. Materials and methods : Models of the screw type implant were used to model the implant as a form placed in the mandibular premolar region applying a three-dimensional finite element method. Screw type implant designs were classified into 4 types of parallel ones and 7 types of tapered ones. Other factors were simulated to represent clinical environment. Results : In parallel implant designs, higher and wider threads resulted in higher insertion torques and higher stress distributions. In tapered implant designs, changes in the taper led to remarkable differences in the insertion torques. It was difficult to determine a certain tendency of stress distribution around the implants since the stress level was too high around them. In tapered implant designs, smaller implants demonstrated lower insertion torques than the original type and were relatively less dependent on the degree of taper. Tapered implants showed higher insertion torques and higher stress distributions than parallel implants. Conclusion : According to this study, although the tapered implant demonstrated a higher insertion torque than the parallel implant, stress tended to be concentrated in the entire fixture of the tapered implant due to the inefficient stress distribution.

• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.3
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• pp.224-235
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• 2013

A passively fitting prosthesis is an essential prerequisite to attain long-lasting success and maintenance of osseointegration. However, true "passive fit" can not be achieved with the present implant-supported prosthesis fabrication protocol. Many clinical situations are suitably treated with cantilevered implant-supported fixed restorations. The purpose of this study was to compare the stress distribution pattern and magnitude in supporting tissues around ITI implants with cantilevered, implant-supported, screw-retained fixed prosthesis according to the fitness of superstructures. Photoelastic model was made with PL-2 resin (Measurements, Raleigh, USA) and three ITI implants (${\phi}4.1{\times}10mm$) were placed in the mandibular posterior edentulous area distal to the canine. Anterior and posterior extended 4-unit cantilevered FPDs were made with different misfit in the superstructures. 4 types of prosthesis were made by placing a $100{\mu}m$ gap between the abutment and the crown on the second premolar and/or the first molar. Photoelastic stress analysis were carried out to measure the fringe order around the implant supporting structure under simulated loading conditions (30 lb).

• Applied Microscopy
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• v.34 no.1
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• pp.1-11
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• 2004

The wound healing is very complex biological processing including inflammatory, reepithelialization and matrix construction. According to the biological systematic category, the ability of the healing is very different. Generally healing ability of the lower animal group has been known more excellent compared to its higher group. Therefore, lower animals have been used as the experimental model to explore the mechanism of the wound healing or repair. To verify histochemical characteristics of the wound healing, we have used skin of the frog (Bombina orientalis) as known common amphibian. At day 1, 10, and 16, the mucous substance was very actively synthesized and strong positive by PAS and Alcian blue (pH 2.5). Day 10 after wounding, margin of the wound was gradually strong positive by PTAH staining for detection of collagen synthesis. At 3 to 6 hour and day 23 to 27, we have found the cell division was active through the MG-P staining, in which the concentration and division of DNA in nucleus was green to deep blue color.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.196-196
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• 2016

치과나 기공소로부터 높은 원가로 인한 재료선택에 어려움을 겪고 있어 귀금속 금합금의 물성을 가질 수 있도록 하면서 가격급등으로 인한 문제 해결하기 위한 비귀금속 합금으로 대체가 필요하기에 이에 따른 연구가 이루어져 국산 제품의 상품화를 위해 파라듐을 이용하여 적합한 새로운 합금을 개발하는 것이 필요하다. 치과용 골드합금은 미국치과의사 협회의 구정에 의하면 1형부터 4형까지 분류하고 있으며 3형에 해당하는 강도와 기계적인 특성을 갖도록 파라듐으로 대체하는 연구가 진행중이거나 시판되고 있다. 따라서 본 연구에서는 2형, 3형 및 4형을 대체가능하도록 팔라듐을 기반으로 한 새로운 합금을 설계하고 합금의 성분원 소인 Au(1~5), Pd(20~25), Ag(70~75), In(1.5) 및 Zn(2)등으로 조성을 변화시켜 측량 후 합금을 제조하기 위하여 아르곤 분위기하의 진공아크용해로를 이용하여 용해하였다. 정량된 금속을 진공아크 용해로에 장입하고 용해는 균질한 합금이 되도록 최소한 6회 이상 용융을 실시하며 합금성분의 손실이 발행하지 않도록 보정을 하였다. 합금의 미세조직 관찰을 위하여 샘플을 고속 다이아몬드 정밀 절단기(Acculom-5, STRUERS, Denmark)를 이용하여 절단한 후 2000 grit의 Sic 연마지에서 단계적으로 $0.3{\mu}m$ 알루미나 분말까지 연마한 후 초음파 세척을 하였다. 준비한 시편은 KCN과 $(NH_4)_2S_2O_8$을 1:1로 혼합한 부식액으로 에칭한 후 OM과 SEM을 이용하여 조직을 관찰하였으며 각 샘플의 성분변화는 EDS 분석을 통해 확인하고 결정구조는 XRD를 사용하여 분석하였다. 경도시험은 비커스경도시험기를 이용하여 5kg의 하중을 30초간 작동시켜 압흔을 연결된 micron으로 평균값을 측정하였다. 각 시편의 부식거동은 POTENTIOSTAT(Model PARSTAT 2273, EG&G, USA)을 이용하여 구강 내환경화 유사한 $36.5{\pm}1^{\circ}C$의 0.9% NaCl에서 실시하였다. 인가전위는 -1500mV에서 1000mV까지 1.67 mV/min의 주사속도로 인가하여 시험을 수행하였으며 분극곡선으로부터 부식전위와 부식전류밀도 및 부동태영역의 전류밀도로 금속의 용출거동을 조사하였으며 부식이 끝난 시편은 FE-SEM과 EDS를 사용하여 조사하였다. 기계적인 특성은 Pd-Ag에 3wt%의 Au를 첨가한 합금이 Pd-Ag에 1.5wt%합금을 첨가한 경우에 비하여 기계적인 특성이 증가하고 내식성이 크게 증가하였다. 이들 합금에 Cu를 11wt%를 첨가한 경우는 비커스경도가 200이상으로 높게 나타났지만 내식성이 크게 감소하였다.