• 한국항공우주학회지
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• 제46권12호
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• pp.1004-1011
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• 2018

최근 우수한 충격 저감 효과로 인해 파이로테크닉 분리 장치의 한 종류인 저충격 파이로 테크닉 분리 너트에 많은 관심이 주어지고 있다. 하지만 파이로테크닉 분리 너트의 경우 일반 너트 대신 분할 너트가 사용되기 때문에 볼트 풀림 거동에 대한 연구가 충분히 이루어지지 않은 측면이 있다. 이에 본 연구에서는 Junker 진동시험을 준거삼아 볼트 풀림 해석을 수행하였다. 해석은 크게 두 단계로 이루어져 있다. 첫 번째 단계는 체결토크를 이용하여 볼트를 분리너트에 체결하는 과정이고, 두 번째 단계는 횡 방향 가진을 통해 볼트가 풀리는 과정이다. 이러한 과정을 통해 볼트 풀림 거동을 얻을 수 있었다. 또한 신뢰성 있는 파이로테크닉 분리 너트의 설계를 위해 체결부 틈새가 볼트 풀림 거동에 미치는 영향을 고찰하였다.

• Journal of Korean Neurosurgical Society
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• 제61권4호
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• pp.494-502
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• 2018

Objective : The loosening of pedicle screws (PS) is one of the frequent problems of spinal surgery in the patients with osteoporosis. Previous studies had revealed that intermittent injection of teriparatide could reduce PS loosening by improving bone mass and quality when their patients took parathyroid hormone for a considerable duration before surgery. However, although the teriparatide is usually used after spine surgery in most clinical situations, there was no report on the efficacy of teriparatide treatment started after spine surgery. The purpose of this retrospective study was to examine the efficacy of teriparatide treatment started immediately after lumbar spinal surgery to prevent pedicle screw loosening in patients with osteoporosis. Methods : We included 84 patients with osteoporosis and degenerative lumbar disease who underwent transforaminal interbody fusion and PS fixation and received parathyroid hormone or bisphosphonate (BP) postoperatively. They were divided into teriparatide group (daily injection of $20{\mu}g$ of teriparatide for 6 months, 33 patients, 172 screws) and BP group (weekly oral administration of 35 mg of risedronate, 51 patients, 262 screws). Both groups received calcium (500 mg/day) and cholecalciferol (1000 IU/day) together. The screw loosening was evaluated with simple radiographic exams at 6 and 12 months after the surgery. We counted the number of patients with PS loosening and the number of loosened PS, and compared them between the two groups. Clinical outcomes were evaluated using visual analog scale (VAS) and Oswestry disability index (ODI) preoperatively, and at 12 months after surgery. Results : There was no significant difference in the age, sex, diabetes, smoking, bone mineral density, body mass index, and the number of fusion levels between the two groups. The number of PS loosening within 6 months after surgery did not show a significant difference between the teriparatide group (6.9%, 12/172) and the BP group (6.8%, 18/272). However, during 6-12 months after surgery, it was significantly lower in the teriparatide group (2.3%, 4/172) than the BP group (9.2%, 24/272) (p<0.05). There was no significant difference in the number of patients showing PS loosening between the teriparatide and BP groups. The teriparatide group showed a significantly higher degree of improvement of the bone mineral density (T-score) than that of BP group (p<0.05). There was no significant difference in the pre- and post-operative VAS and ODI between the groups. Conclusion : Our data suggest that the teriparatide treatment starting immediately after lumbar spinal fusion surgery could reduce PS loosening compared to BP.

• 한국지반공학회논문집
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• 제30권8호
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• pp.13-24
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• 2014

지반아칭을 규명하기 위해 일련의 트랩도어 모형실험을 실시하였다. 이 모형실험에서 지반아칭현상은 모형토조바닥에 작용하는 연직토압의 변화를 관찰함으로서 확인할 수 있었다. 트랩도어 재하판의 하강으로 지반변형을 발생시킴으로서 트랩도어 상부지반에 이완영역이 발생하였다. 이때 이완영역내의 응력은 지반아칭현상에 의해 트랩도어 주변의 정지영역으로 전이됨을 알 수 있었다. 즉 연직토압은 이완영역 내에서는 급격히 감소하였고 정지영역에서는 크게 증가하였다. 이완영역 내 연직토압의 최대감소율과 정지영역에서의 연직토압의 최대증가율은 지반밀도에는 영향을 받지 않았으나 트랩도어 재하폭의 크기에는 영향을 크게 받았다. 이완영역은 타원형상으로 정의할 수 있었으며 이타원의 장축은 트랩도어 중앙에서의 이완영역높이의 두 배 크기에 해당하였고 단축은 트랩도어 폭 크기에 해당하였다. 여기서 트랩도어 중앙에서의 이완영역높이는 트랩도어 폭의 1.5배 크기로 나타났다.

• 대한치과보철학회지
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• 제38권6호
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• pp.765-781
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• 2000

The purpose of this study was to compare the screw loosening characteristics of three avail-able cementation type abutments: one-piece cementation type abutment; two-piece cementation type abutment using titanium abutment screw; two-piece cementation type abutment using gold abutment screw. Two implant supported three-unit superstructures were fabricated using a pair of 3 kinds of abutments for each experimental model. Cyclic loading was applied on the specimen, and made to stop when the superstructure showed movement over threshold range. The loaded cycle was counted until the machine stopped. Frequency analysis was done to measure the change of natural frequency before and after the application of cyclic load and to find the effect of screw loosening on the change of natural frequency. The specimen assembly was modeled to perform the finite element analysis to see the distribution of the stress induced by the application of preload over the screw joint and to compare the pattern of the distribution of stress induced by the external force with the change of the preload condition. The following results were obtained: 1. The failure loading cycle of two-piece cementation type abutment using gold screw was significantly greater than those of the other groups. 2. One-piece cementation type abutment applied to multi-unit restoration case did not show greater resistance to screw loosening compared to two-piece cementation type abutments. 3. Frequency analysis showed decrease in natural frequency when screw loosening occured.

• 대한치과보철학회지
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• 제45권3호
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• pp.345-353
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• 2007

Statement of problem. Implant abutment screw joints tend to loosen under clinical conditions. Abutment screw loosening results in loss of preload in function. Purpose. Anti-rotational inner post screw (ARIPS) systems were compared with conventional abutment screws to reduce screw loosening. Reverse torque values were evaluated. Material and methods. 32 implant assemblies (Warentec, Co, Ltd, Seoul, Korea) were organized as the 30-Ncm-torque conventional groups and 30-Ncm-torque ARIPS groups in external and internal system. The specimens were tested to 106 cycles at a load of 200N. Preload reverse torque, postload reverse torque, and the ratio of postload reverse torque to preload reverse torque were evaluated. The data were analyzed with unpaired t-test in external and internal systems. Results. In the ratio of postload reverse torque to preload reverse torque, the ARIPS groups showed significant differences than the conventional screw group in both external and internal system. Conclusion. Within the limitations of this study, abutment screw loosening was effectively reduced using ARIPS system.

• Geomechanics and Engineering
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• 제38권6호
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• pp.571-581
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• 2024

Concrete linings in tunnels constructed by drilling and blasting such as NATM serve as a secondary support structure. However, these linings can face unexpected earth pressures if the primary support deteriorates or if ground conditions become unfavorable. It is crucial to determine the loosening earth pressure that allows the lining to maintain its structural integrity and prevent damage caused by this pressure. This study proposes a numerical model for simulating the trapdoor test and developing a method for calculating the loosening earth pressure. The discrete element method (DEM) was employed to describe the soil characteristics around the tunnel. Using this numerical model, a sequence of experimental trapdoor steps was simulated, and the loosening earth pressure was analyzed. Contact parameters were calibrated based on an analysis of a triaxial compression test. The reliability of the developed model was confirmed through a comparison between simulation results and laboratory test findings. The model was used to calculate the contact force applied to the trapdoor plate and to assess the settlement of soil particles. Furthermore, the model accounted for the soil-arching effect, which effectively redistributes the load to the surrounding areas. The proposed model can be applied to analyze the tunnel's cross-sectional dimensions and design stability under various ground conditions.

• 대한치과의사협회지
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• 제53권5호
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• pp.307-317
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• 2015

Although the long-term success of osseointegrated endosseous implants for the support of fixed dental prostheses has been reported, the increasingly widespread use of implant-supported prostheses has led to problems associated with their structural integrity. The most common biomechanical complications observed in dental implant treatment are fracture and screw loosening. The nature of loosening or fracture of dental implant components is complex, since it involves fatigue, fitness, and varied chewing patterns and loads. To assess the service life of the components of the prosthetic system, a knowledge of the loads transmitted through the system is necessary. Design of the final restoration and occlusion in relation to the geometry of a prosthetic restoration has a great influence on the mechanical loading of the implant. It is proposed that control of force in oral cavity may play a larger role in failures than previously believed. Based on theoretic consideration and clinical experiences with dental implant, this article gives simple guidelines for controlling these loads.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1993년도 Proceedings of International Conference for Agricultural Machinery and Process Engineering
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• pp.994-1002
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• 1993

Soil deep loosening technique can improve the soil structure and increase the air permeability and water permeability of soil. It can increase the yield of crops in a large scale, particularly the plants with deep root system. This paper introduced the study on the deep loosening technique of sugarcance in Jinpen Farm where the soil is heavy caly with high ground water table. The implement and method of deep loosing, the experiments and results are include in this paper. The experimental results showed that the yield of sugarcane increased more than 20% after deep loosing.

• 대한치과보철학회지
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• 제40권2호
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• pp.193-200
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• 2002

For the purpose of decreasing the chair time in implant cases, the time needed to loosening and fastening the screw must be shortened. Nowadays, the two typical designs of screw head are slot and hexa form. This study aimed at the shortening of loosening and fastening time by modifying the slot and hexa form. Total of twelve dentists participate in these experiments, four of them were experienced and eight of them were novice dentists. 1. There were many differences in the speeds of screw loosening and fastening between personal experiences. Experienced dentists are faster than novice dentists. 2. There were many differences in the speeds by angulation of the implant, by the conditions of the muscle tonicity. 3. Revised slot and hexa Heads show the slightly shortened time for acrew looseing and fastening.

• The Journal of Advanced Prosthodontics
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• 제5권1호
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• pp.21-28
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• 2013

PURPOSE. This study examined the effects of the abutment types and dynamic loading on the stability of implant prostheses with three types of implant abutments prepared using different fabrication methods by measuring removal torque both before and after dynamic loading. MATERIALS AND METHODS. Three groups of abutments were produced using different types of fabrication methods; stock abutment, gold cast abutment, and CAD/CAM custom abutment. A customized jig was fabricated to apply the load at $30^{\circ}$ to the long axis. The implant fixtures were fixed to the jig, and connected to the abutments with a 30 Ncm tightening torque. A sine curved dynamic load was applied for $10^5$ cycles between 25 and 250 N at 14 Hz. Removal torque before loading and after loading were evaluated. The SPSS was used for statistical analysis of the results. A Kruskal-Wallis test was performed to compare screw loosening between the abutment systems. A Wilcoxon signed-rank test was performed to compare screw loosening between before and after loading in each group (${\alpha}$=0.05). RESULTS. Removal torque value before loading and after loading was the highest in stock abutment, which was then followed by gold cast abutment and CAD/CAM custom abutment, but there were no significant differences. CONCLUSION. The abutment types did not have a significant influence on short term screw loosening. On the other hand, after $10^5$ cycles dynamic loading, CAD/CAM custom abutment affected the initial screw loosening, but stock abutment and gold cast abutment did not.