• Title/Summary/Keyword: CT 시편

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Comparison of TheraCal LC, Mineral trioxide aggregate, and Formocresolas pulpotomy agents in rat molar (백서에서 치수절단술에 사용하는 TheraCal LC, MTA 그리고 Formocresol의 비교)

  • Lee, Bin-Na;Song, Young-Sang;Lee, Go-Woon;Kim, Young-Hoon;Chang, Hoon-Sang;Hwang, Yun-Chan;Oh, Won-Mann;Hwang, In-Nam
    • Korean Journal of Dental Materials
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    • v.44 no.2
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    • pp.187-195
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    • 2017
  • TheraCal LC, a new light-cured, resin-modified calcium silicate-filled base/liner material, has been introduced as a pulpotomy agent. The aim of this study was to evaluate the capacity of hard tissue formation and pulpal response after pulpotomy with TheraCal LC. Twenty-two 9-week-old male rats were anesthetized, cavities were prepared in maxillary first molars and pulps were capped with formocresol (FC), mineral trioxide aggregate (MTA), and TheraCal LC. Specimens obtained from rats were scanned using a high-resolution micro CT system. The specimens were prepared and evaluated histologically, and immunofluorescence assay was performed to assess the dentin matrix protein-1 (DMP-1) expression. On micro CT analysis, the MTA and TheraCal LC groups showed thicker hard tissue formation than the FC group. On hematoxylin and eosin (H&E) staining, MTA and TheraCal LC groups showed dentine bridge formation with vital pulp beneath the materials. On immunofluorescence analysis, DMP-1 was highly expressed in the TheraCal LC group compared to the FC group. TheraCal LC showed similar capacity to form hard tissue as MTA when it was used as a pulpotomy agent. Because of its good manipulation and faster setting time compared to MTA, TheraCal LC could be considered as a good alternative to MTA.

Evaluation of Crack Length and Thickness Effects of Fracture Specimen using Damage Mechanics (손상역학에 근거한 파괴시편의 균열길이와 두께 영향 평가)

  • Chang Yoon-Suk;Lee Tae-Rin;Choi Jae-Boong;Seok Chang-Sung;Kim Young-Jin
    • Journal of the Korean Society for Precision Engineering
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    • v.23 no.4 s.181
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    • pp.116-123
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    • 2006
  • During the last two decades, many researchers investigated influences of stress triaxiality on ductile fracture for various specimens and structures. With respect to a transferability issue, the local approach reflecting micro-mechanical specifics is one of effective methods to predict constraint effects. In this paper, the applicability of the local approach was examined through a series of finite element analyses incorporating modified GTN (Gurson-Tvergaard-Needleman) and Rousselier models as well as fracture toughness tests. To achieve this goal, fracture resistance (J-R) curves of several types of compact tension (CT) specimens with various crack length, with various thickness and with/without 20% side- grooves were estimated. Then. the constraint effects were examined by comparing the numerically estimated J-R curves with experimentally determined ones. The assessment results showed that the damage models might be used as useful tool for fracture toughness estimation and both the crack length and thickness effects should be considered for realistic structural integrity evaluation.

Extended Compliance Solution of ESET Specimen for Thermal fatigue Crack Growth Test (열피로 균열성장시험을 위한 ESET 시편의 확장된 컴플라이언스 해)

  • Lee, Ho-Jin;Kim, Maan-Won;Lee, Bong-Sang
    • Journal of the Korean Society of Safety
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    • v.20 no.1 s.69
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    • pp.62-67
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    • 2005
  • An eccentrically-loaded single edge crack tension specimen (ESET) is similar to a compact tension(CT) specimen loaded in tension-tension. The standard ESET specimen exhibits advantages over other types of cracked specimen, such as n, single-edge crack, and middle-crack tension specimen. The details of ESET specimen configuration, test procedure, and calculations are described in ASTM E647 standard. However, a difficulty in attaching COD gage to the knife-edge on the front foe of the specimen can be found when the size of ESET specimen is small for rapid cooling and heating in thermal fatigue testing. The finite element analysis is performed for the ESET specimen with projected knife-edge on the front foe and a crack-length-compliance equation is suggested for the new specimen configuration. Calibration test are conducted with 347 stainless steel to compare the measured crack length with the calculated crack length from the suggested compliance expression. The test results showed good agreements with those of analysis.

Evaluation of marginal leakage of bulk fill flowable composite resin filling with different curing time using micro-computed tomography technology (Bulk fill 유동성 복합레진의 변연 누출에서 다른 중합시간의 영향에 대해 마이크로시티를 이용한 평가)

  • Kim, Eun-Ji;Lee, Kyu-Bok;Jin, Myoung-Uk
    • Journal of Dental Rehabilitation and Applied Science
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    • v.32 no.3
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    • pp.184-193
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    • 2016
  • Purpose: To evaluate marginal leakage of bulk fill flowable composite resin filling with different curing time by using microcomputed tomography technology. Materials and Methods: 30 previously extracted human molars were randomly divided into 6 groups based upon restorative system and different curing time. Class II cavities (vertical slot cavities) were prepared. An individual metallic matrix was used to build up the proximal wall. The SonicFill or SureFil SDR flow was inserted into the preparation by using 1 bulk increment, followed by light polymerization for different curing times. The different exposure times were 20, 40, and 60 seconds. All specimens were submitted to 5,000 thermal cycles for artificial aging. Micro-CT scanning was performed by using SkyScan 1272. One evaluator assessed microleakage of silver nitrated solution at the resin-dentin interface. The 3D image of each leakage around the restoration was reconstructed with CT-Analyser V.1.14.4. The leakage was analyzed with the Mann-Whitney test. Results: Significant differences were observed between the light curing times, but no significant differences were found between the bulk fill composite resins. Increasing in the photoactivation time resulted in greater microleakage in all the experimental groups. Those subjected to 60 seconds of light curing showed higher microleakage means than those exposed for 20 seconds and 40 seconds. Conclusion: Increasing the photoactivation time is factor that may increase marginal microlekage of the bulk fill composite resins. Further, micro-CT can nondestructively detect leakage around the resin composite restoration in three dimensions.

Correlation Between Transient Regime and Steady-State Regime on Creep Crack Growth Behavior of Grade 91 Steel (Grade 91 강의 크리프 균열성장 거동에 대한 천이영역과 정상상태영역의 상관 관계)

  • Park, Jae-Young;Kim, Woo-Gon;Ekaputra, I.M.W.;Kim, Seon-Jin;Kim, Eung-Seon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.12
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    • pp.1257-1263
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    • 2015
  • A correlation between the transient regime and steady state regime on the creep crack growth (CCG) for Grade 91 steel, which is used as the structural material for the Gen-IV reactor systems, was investigated. A series of CCG tests were performed using 1/2" CT specimens under a constant applied load and at a constant temperature of $600^{\circ}C$. The CCG rates for the transient and steady state regimes were obtained in terms of $C^*$ parameter. The transient CCG rate had a close correlation with the steady-state CCG rate, as the slope of the transient CCG data was very similar to that of the steady state data. The transient rate was slower by 5.6 times as compared to the steady state rate. It can be inferred that the steady state CCG rate, which is required for long-time tests, can be predicted from the transient CCG rate obtained from short-time tests.

THE ANTICARIOGENIC EFFECT OF RESIN INFILTRATION ACCORDING TO THE PRETREATMENT OF SURFACE LAYERS IN NATURAL INCIPIENT CARIES LESIONS (초기 우식 병소의 표층 처리에 따른 Resin infiltration의 우식 저지 능력 평가)

  • Kim, Min-Jeong;Lee, Dong-Soo;Kim, Shin;Jeong, Tae-Sung
    • Journal of the korean academy of Pediatric Dentistry
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    • v.37 no.4
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    • pp.412-421
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    • 2010
  • As a most conservative, minimally invasive trial against early caries lesions, resin infiltration concept has been introduced and studied mainly about effective materials and pre-treatment methods of surface layers to arrest the lesion effectively, which is still going on. This study was performed with an aim of evaluating the efficacy of arresting the caries process in the natural incipient lesions in spite of removing the surface layers and we obtained the results as follows: 1. It was revealed that infiltration groups(1, 3, 5) showed lower radio-density decline between pre- and posttreatment than control groups(2, 4, 6)(p<0.05). 2. Group 5, in which the surface layer was removed with hydrochloric acid, showed the most significant anticariogenic effect(p<0.05). 3. Under SEM evaluation after infiltration, group 1 and 3 showed more irregular destruction and intensive loss of surface layers than group 5. In conclusion, it was thought resin infiltration can be an effective tool against the early caries lesions although surface layers are removed.

Stress Analysis and Fatigue Failure of Prefabricated and Customized Abutments of Dental Implants (치과 임플란트에서 기성 지대주와 맞춤형 지대주의 응력분석 및 피로파절에 관한 연구)

  • Kim, Hee-Eun;Cho, In-Ho
    • Journal of Dental Rehabilitation and Applied Science
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    • v.29 no.3
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    • pp.209-223
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    • 2013
  • This study was to evaluate the stress distributions of prefabricated, customized abutments and fixtures according to their material and shape by three-dimensional finite element analysis. And to investigate the fatigue life and fracture characteristics. Mandibular models were fabricated by reconstruction of the CT scan of patients with normal occlusion. A total of six finite element models were designed, a load of 100 N was applied on the buccal cusps vertically, and 30 degree obliquely. 10 specimens each were fabricated for the more clinically widely used 4 type abutments and were loaded according to ISO 14801. Differences in stress distribution patterns were not found according to the materials of the abutments and fixtures. But a slight difference in the stress level was detected. Customized abutment groups showed lower crown stress levels. One-piece zirconia implant showed the lowest bone stress levels. In the fatigue test, highest values were measured in group 7. Prefabricated abutments showed less variation of fatigue life (P<0.05). Use of customized abutments can improve the fracture resistance of restorations. Especially, use of customized zirconia abutments reinforced by titanium screw connecting parts is recommended.

Evaluation of Cavity Wall Adaptation of Bulk-fill Resin Composites in Class II Cavities of Primary Molar (유구치 2급 와동에서 bulk-fill 복합레진의 와동적합성 평가)

  • Bae, Youngeun;Shin, Jonghyun;Kim, Shin;Jeong, Taesung;Kim, Jiyeon
    • Journal of the korean academy of Pediatric Dentistry
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    • v.44 no.4
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    • pp.446-454
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    • 2017
  • Recently, there have been many studies on bulk-fill resin composites. However, studies on the proper materials for pediatric patients are rare. The aim of this study was to compare the cavity wall adaptation of bulk-fill resin composites with conventional resin composite in class II cavities of primary molars using microcomputed tomography (micro-CT). Standardized class II slot cavities were prepared in 80 exfoliated primary molars and randomly divided into 4 groups. The control group was restored with conventional resin composite, Filtek Z-350 XT (FZ), and the three groups were restored with bulk-fill resin composites, Filtek bulk-fill posterior (FB), Tetric N-Ceram Bulk Fill (TNC), Filtek bulk-fill flowable (FBF). All specimens were thermocycled and then immersed in 50% silver nitrate ($AgNO_3$) solution. Micro-CT was used to measure the penetration volume of the total silver nitrate and the degree of cervical marginal leakage and the number, size, and position of the voids were evaluated. The results revealed that the volume of silver nitrate were significantly different between FB and FZ (p < 0.05). The results also revealed that the penetration length of silver nitrate FBF showed statistically lower than the FZ and FB (p < 0.05). There was no significant difference between the groups in number and size of voids. In conventional resin composite, most of the voids were present inside the restoration (83.3%), but the voids in the bulk-fill resin composites incidence were higher in the gingivoaxial angle. The cavity wall adaptation demonstrated in class II restorations of primary molar by new bulk fill resin composites was similar to conventional incremental technique. Bulk-fill resin composites might be an clinical option for a faster restoration in deciduous teeth.

Electrical characteristics for Multi-Nanocomposites throuh Surface Control of Epoxy/Nano_Micro $SiO_2$ Particles (Epoxy/Nano_Micro $SiO_2$입자 표면제어를 통한 멀티-나노콤포지트 전기적 특성연구)

  • Park, Young-Byum;Park, Hyun-Su;O, Chung-Yon;Kim, Hak-Jae;Park, Ki-Ryung;Lee, Dae-Kyoung;Park, Jae-Jun
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2009.11a
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    • pp.154-154
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    • 2009
  • 본 연구는 고전압 전력기기인 몰드형변압기와 계기용 변성기인 CT, PT 절연특성에 유용한 Epoxy/Nano-Micro Mixture Composites(이하,ENMMC)를 개발하기위해 무엇보다 중요한 것은 Nano입자인 $SiO_2$_10nm입자의 표면을 제어하여 즉, 표면의 소수성을 크게 하여 나노입자의 균질한 분산을 얻은것이 무엇보다 중요하다. 개발된 Epoxy/$SiO_2$_10nm Nanocomposites와 Microcomposites을 기계적 전단응력을 이용하여 균질 혼합을 실시하였다. 이런 조건을 이용한 전기적특성을 측정하기위해 구대구 전극이 완전함침된 평등전계하에서 절연파괴전압을 측정하기 시편을 제조하였다. 마이크로입자의 충진함량을 일정하게 유지하여 나노입자 충진함량비율을 4가지로 변화시켜 절연파괴특성을 연구하였다. 충진함량이 나노입자의 경우 1wt%이하의 값이 상대적으로 우수한 절연파괴특성으로 와이블 플롯을 통하여 알수있었다. 상대적으로 멀티나노콤포지트의 형상파라미터가 큰 결과값을 얻을수 있었다. 그리고 스케일파리미터는 누적확률 밀도함수로서 63.2%에서 대단히 큰 초절연성의 절연소재를 개발할수 있었다.

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Development of Finite Element Ductile Tearing Simulation Model Considering Strain Rate Effect (변형률 속도를 고려한 유한요소 기반 연성 찢김 해석 기법 개발)

  • Nam, Hyun Suk;Kim, Ji Soo;Kim, Jin Weon;Kim, Yun Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.2
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    • pp.167-173
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    • 2016
  • This paper proposes ductile failure simulation under high strain rate conditions using finite element (FE) analyses. In order to simulate a cracked component under a high strain rate condition, this paper applies the stress-modified fracture strain model combined with the Johnson/Cook model. The stress-modified fracture strain model determines the incremental damage in terms of stress triaxiality (${\sigma}_m/{\sigma}_e$) and fracture strain (${\varepsilon}_f$) for a dimple fracture using the tensile test results. To validate the stress-modified fracture strain model under dynamic loading conditions, the parameters are calibrated using the tensile test results under various strain rates and the fracture toughness test results under quasi-static conditions. The calibrated damage model predicts the CT test results under a high strain rate. The simulated results were then compared with the experimental data.