• Journal of the korean academy of Pediatric Dentistry
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• v.45 no.1
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• pp.123-130
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• 2018

In the root fracture, pulp necrosis tends to involve only the coronal fragment, while the pulp in the apical fragment remains vital. The prognosis of endodontic treatment of the apical fragment is poor due to the possibility of overfilling of the space between the fragments and difficulty in removing necrotic tissue. In the present cases, endodontic treatment of the apical fragment of root fracture was performed. However, in reendodontic treatment, resistance was felt at the fracture site and access to the root canal in the apical fragment was difficult. Therefore, the calcium hydroxide was periodically exchanged only in the coronal fragment without further treatment in the apical fragment and the canal of the coronal fragment was finally filled with Gutta-percha. Regular observation revealed no radiologic complications in the apical fragment. In some cases, we can observe good healing pattern such as absorption of calcium hydroxide and pulp canal obliteration of apical fragment in the long term.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.233-244
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• 2017

We conducted hydraulic fracturing experiments on cement samples to investigate the dependency of fracture propagation on the viscosity of injection fluid and the in situ stress state. Ten cubic samples (20 cm side length) were produced using cement that was cured in water for more than one month. Samples were placed in a tri-axial compression apparatus with three independent principal stresses. An injection hole was drilled and the sample was hydraulically fractured under a constant injection rate. We measured injection pressures and acoustic emissions (AE) during the experiments, and investigated the fracture patterns produced by hydraulic fracturing. Breakdown pressures increased exponentially with increasing viscosity of the injection fluid. Fracture patterns were dependent on differential stress (i.e., the difference between the major and minor principal stresses). At low differential stress, multiple fractures oriented sub-parallel to the major principal stress axis propagated from the injection hole, and in some samples the fracture orientation changed during propagation. However, at high differential stress, a single fracture propagated parallel to the major principal stress axis. AE results show similar patterns. At low differential stress, AE source locations were more widespread than at high differential stress, consistent with the fracture pattern results. Our study suggests that hydraulic fracturing during shale gas extraction should be performed parallel to the orientation of minimum differential stress.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.40 no.1
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• pp.21-26
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• 2014

Objectives: The purpose of this article is to analyze the incidence, demographic distribution, type, and etiology of mandible fractures that were treated by the Department of Oral and Maxillofacial Surgery in Kyung Hee University Dental Hospital from January 2002 to December 2012. Materials and Methods: This was a descriptive and analytic retrospective study that evaluated 735 patients that were treated for mandible fracture. Results: This study included 1,172 fractures in 735 patients. The ratio of male to female patients was 5.45 : 1; the maximum value was in patients between 20 and 29 years (38.1%) and the minimum in patients over 70 years old. The monthly distribution of facial fractures peaked in the fall and was lower during winter. No specific correlation was identified based on the annual fracture distribution. Among the 735 fracture patients, 1.59 fracture lines were observed per patient. The most frequent site was the symphysis, which accounted for a total of 431 fractures, followed by the angle (348), condyle (279), and body (95). The symphysis with angle was the most common site identified in combination with fracture and accounted for 22.4%, followed by symphysis with condyle (19.8%). The angle was the most frequent site of single fractures (20.8%). The major cause of injury was accidental trauma (43.4%), which was followed by other causes such as violence (33.9%), sports-related accidents (10.5%), and traffic accidents (10.1%). Fracture incidents correlated with alcohol consumption were reported between 10.0%-26.9% annually. Conclusion: Although mandible fracture pattern is similar to the previous researches, there is some changes in the etiologic factors.

• Clinics in Shoulder and Elbow
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• v.10 no.2
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• pp.199-203
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• 2007

Purpose: It is very important to evaluate and fix coronoid process fractures because they are a critical element for a stable, effective elbow function. The lateral view of the elbow joint is used for a radiographic evaluation of the coronoid but an understanding of the fracture pattern is often difficult because of overlap of the radial head and obliquity of the fracture line. We developed the coronoid view, which is a new radiograph for an evaluation of the coronoid process fracture, and discuss its advantages for a postoperative follow-up. Materials and Methods: The coronoid view was designed for an evaluation of the anteromedial fragment of the coronoid process. After the patient sat on his side, the shoulder was abducted $45^{\circ}$ and the elbow was flexed $90^{\circ}$. The X-ray beam was shot perpendicular to the table. Since shoulder was abducted $45^{\circ}$ the fracture line of the coronoid process can be parallel to the X-ray beam, and the radial head can be cleared. Conclusion: The coronoid view can be a good alternative radiograph for an evaluation of a coronoid process fracture because the beam is parallel to the fracture line. The coronoid view can be particularly useful in postoperative patient follow-up where computed tomography is impractical due to metal implants and cost.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.668-671
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• 1995

In this study, the fatigue charateristics of weld specimen was studied experimentally by using the various specimen types. The specimen type were tensile shesr(TS) specimen, cross tension(CT) specimen, and T typr (TT) specimen. Tensile test and fatigue test were carried out and microstucture was investigated. Finite element method was used to investigate stress distribution near nugget edge. Finally fracture mechanics approach was tried to the various specimen types.

• Transactions of Materials Processing
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• v.12 no.3
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• pp.228-235
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• 2003

In this paper, the workability of flange in the radial extrusion is analyzed in terms of the deformation pattern, the punch load and the forming limit by using simulation and experiment. A single action pressing is applied to both simulation and experiment. The analysis in this study is focused on the transient extrusion into the gap in radial direction with various gap heights and die corner radius. Based on the surface strains where surface cracking occurs, the forming patterns and strain-fracture relationships in producing radially extruded flange are obtained.

• Proceedings of the KACD Conference
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• 2004.05a
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• pp.304-308
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• 2004

Maxillary anterior crown fractures are a common form of injury that mainly affects children and adolescents. The position of maxillary incisors and their eruptive pattern carries a significant risk for trauma. In the pre-adhesive era, fractured teeth needed to be restored either with pin-retained inlays or cast restorations that sacrificed healthy tooth structure and were a challenge for dentists to match with adjacent teeth. But. recently the development of adhesive dentistry has allowed dentists to use the patient's own fragment to restore the fractured tooth. The purpose of this paper is to present 2 cases of reattachment of fractured teeth which had different fracture mode, and to evaluate prognosis of cases.

• Journal of the Korean Society of Safety
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• v.28 no.6
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• pp.57-63
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• 2013

This paper discusses 2D models of beams for simulating the fracture of brittle materials. A simulation of an experiment on a concrete beam subjected to bending, in which two overlapping cracks occur, is used to study the effect of individual beam characteristics and different arrangements of the beams in the overall network mesh. It was found that any regular orientation of the beams influences the resulting crack patterns. Methods to implement a wide range of poisson's ratios are also developed, the use of the mesh to study arbitrary micro-structures is outlined. The crack pattern that are obtained with mesh are in good agreement with the experimental results. Also, numerical simulations of the tests were performed by means of a model, and non-integer dimensions were measured on the predicted mesh damage patterns.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2011.09a
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• pp.3-21
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• 2011

Laboratory experiments and numerical simulations using Particle Flow Code (PFC2D) were performed to study the effects of joint separation and joint overlapping on the full failure behavior of rock bridges under direct shear loading. Through numerical direct shear tests, the failure process is visually observed and the failure patterns are achieved with reasonable conformity with the experimental results. The simulation results clearly showed that cracks developed during the test were predominantly tension cracks. It was deduced that the failure pattern was mostly influenced by both of the joint separation and joint overlapping while the shear strength is closely related to the failure pattern and its failure mechanism. The studies revealed that shear strength of rock bridges are increased with increasing in the joint separation. Also, it was observed that for a fixed cross sectional area of rock bridges, shear strength of overlapped joints are less than the shear strength of non-overlapped joints.

• Journal of the Korean Society of Groundwater Environment
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• v.6 no.1
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• pp.1-7
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• 1999

This study deals with linear flow pattern in steady-state or transient dual-porosity media with a vertical geologic structure such as fault, fracture zone, etc. A pumping well is located in the vertical structure of infinitesimal or finite width with high hydraulic conductivity and negligible specific storage. Selected type curves on a pumping well and observation wells in the fractured system and the matrix block are provided. The type curves on the pumping well considers both wellhole and well-loss effects.