• Journal of Korean Neurosurgical Society
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• v.58 no.4
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• pp.357-362
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• 2015

Objective : To investigate risk factors for S1 screw loosening after lumbosacral fusion, including spinopelvic parameters and paraspinal muscles. Methods : We studied with 156 patients with degenerative lumbar disease who underwent lumbosacral interbody fusion and pedicle screw fixation including the level of L5-S1 between 2005 and 2012. The patients were divided into loosening and non-loosening groups. Screw loosening was defined as a halo sign larger than 1 mm around a screw. We checked cross sectional area of paraspinal muscles, mean signal intensity of the muscles on T2 weight MRI as a degree of fatty degeneration, spinopelvic parameters, bone mineral density, number of fusion level, and the characteristic of S1 screw. Results : Twenty seven patients showed S1 screw loosening, which is 24.4% of total. The mean duration for S1 screw loosening was $7.3{\pm}4.1$ months after surgery. Statistically significant risk factors were increased age, poor BMD, 3 or more fusion levels (p<0.05). Among spinopelvic parameters, a high pelvic incidence (p<0.01), a greater difference between pelvic incidence and lumbar lordotic angle preoperatively (p<0.01) and postoperatively (p<0.05). Smaller cross-sectional area and high T2 signal intensity in both multifidus and erector spinae muscles were also significant muscular risk factors (p<0.05). Small converging angle (p<0.001) and short intraosseous length (p<0.05) of S1 screw were significant screw related risk factors (p<0.05). Conclusion : In addition to well known risk factors, spinopelvic parameters and the degeneration of paraspinal muscles also showed significant effects on the S1 screw loosening.

• Smart Structures and Systems
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• v.18 no.4
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• pp.643-662
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• 2016

The monitoring of structural integrity of pipeline tapered thread connections is of great significance in terms of safe operation in the industry. In order to detect effectively the loosening degree of tapered thread connection, an active sensing method using piezoceramic transducers was developed based on time reversal technique in this paper. As the piezoeramic transducers can be either as actuators or sensors to generate or detect stress waves, the energy transmission for tapered thread connection was analyzed. Subsequently, the detection principle for tapered thread connection based on time reversal was introduced. Finally, the inherent relationship between the contact area and tightness degree of tapered thread connection for the pipe structural model was investigated. Seven different contact area scenarios were tested. Each scenario was created by loosening connectors ranging from 3 turns to 4.5 turns in the right tapered threads when the contact area in the left tapered threads were 4.5 turns. The experiments were separately conducted with a highly noisy environment and various excitation signal amplitudes. The results show the focused peaks based on time reversal have the monotonously rising trend with the increase of the contact areas of tapered threads within an acceptable monitoring resolution for metal pipes. Compared with the energy method, the proposed time reversal based method to monitor tapered threads loosening demonstrates to be more robust in rejecting noise in Structural Health Monitoring (SHM) applications.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.3
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• pp.227-237
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• 2005

In this study, the behavior of shallow 2-Arch tunnel due to excavation under horizontal discontinuity plane was verified experimentally. The model tests were carried out by varying the overburden height and the location of the discontinuity plane. The model tests followed exactly the real 2-Arch tunnel construction stages. As a result, it is discovered that stress-transfer mechanism and loosening area around the 2-Arch tunnel depends on the overburden heights and the location of the discontinuity plane. And central pillar load is also dependent on overburden height, location of discontinuity plane and construction stages.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.2
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• pp.174-184
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• 2006

Purpose: Current trend in implant dentistry is changing from external connection to internal connection. To evaluate the splinting of external and internal connection implant on screw loosening, 2-units prosthesis was fabricated with BioPlant $System^(R)$ of external connection type and Lifecore STAGE-1 Single Stage Implant $System^(R)$ of internal connection type. Material and Method: Experimental group is classified into three groups. 1) $G_1-EE$: 2-units prosthesis was fabricated with two Bioplant $System^(R)$ of external connection type. 2) $G_1-EI$: 2-units prosthesis was fabricated with one BioPlant $System^(R)$ of external connection type and one Lifecore STAGE-1 Single Stage Implant $System^(R)$ of internal connection type. 3) $G_1-II$: 2-units prosthesis was fabricated with two Lifecore STAGE-1 Single Stage Implant $System^(R)$ of internal connection type. In fabricating 2-units prosthesis, two hexed abutments are recommended when two implants are installed parallel, otherwise one hexed abutment is used on major occlusal force area and one nonhexed abutment is used on the other area. Since it is rare to find two implants being parallel, it is hard to fabricate prosthesis with passive adaptation using two hexed abutments. It is much more difficult to acquire passive adaptation when using hex abutment compared to nonhex abutment. To evaluate the influence of hexed and nonhexed abutment on screw loosening, 2-units prosthesis was fabricated with hexed and nonhexed abutment. Experimental group is classified into three groups. 1) $G_2-HH$: 2-units prosthesis was fabricated with two hexed abutments. 2) $G_2-HN$: 2-units prosthesis was fabricated with one hexed abutment and one nonhexed abutment. 3) $G_2-NN$: 2-units prosthesis was fabricated with two nonhexed abutments. Result: The results of comparing the detorque value after loading on a each prosthesis periodically are as follows. 1. In splinting group of external and internal connection implant, $G_1-II$ group demonstrated the biggest detorque value, followed by $G_1-EI$ group and $G_1-EE$ group. 2. There is no notable significance between external connection implant of $G_1-EI$ group and $G_1-EE$ group and also no significance between internal connection implant of $G_1-EI$ group and $G_1-II$ group. 3. $G_2-HH$ group showed higher detorque value than $G_2-HN\;and\;G_2-NN$ group. From the results, we can concluded that using both external connection and internal connection implant together is clinically acceptable and in order to acquire a good passive adaptation in fabricating 2-units implant prosthesis we can use two nonhexed abutments.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.299-306
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• 2019

In this study, a model experiment that simulates the behaviour of the ground composed of several compacted layer was intended to measure the loosened area in the event of a ground cavity through a LAD (Loosened area detector). It was confirmed that the size of the cone diameter was affected by the ground composed of fine grain + granulated soil layered through the model soil. In order to select the appropriate cone type, a scale effect experiment was conducted. From the test results, a micro-cone was chosen for the most suitable indoor model experiment. In the case of applying LAD in this study, the loosening condition of the ground was determined by the rapid change in penetration resistance caused by the difference in the boundary surface and relative density due to the compaction of the ground for indoor model testing. The range of loosened area occurring in the cavity was estimated through the penetration resistance characteristics on the ground, and the failure area was identified through the reduction rate of penetration resistance in the loosening area.

• Journal of the Korean Society of Safety
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• v.19 no.1
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• pp.12-17
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• 2004

By using an experimental approach recently developed to determine the torque-tension relationship for bearing frictional characteristics of several typical bolted joints were studied. The experimental approach allows the direct determination of the bearing friction between the nut and its bearing surface. Detailed friction studies were made on the influences of the size and shape of the hole, the use of a slot in a bolted joint, contact area and position, and other factors such as turning speed, coating, and the use of wax on the bearing surface. The contact area and position of the washer have a marginal effect on the bearing friction. The organic coating on the nuts reduces the bearing friction significantly. Nuts with organic coating over a washer with zinc finish provide the smallest and the most consistent bearing friction. The results from the experimental investigation will be helpful for the better design of bolted joints bearing friction. The results from the experimental investigation Will be helpful for the better design of bolted joints.

• The Journal of Korean Academy of Prosthodontics
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• v.54 no.4
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• pp.387-392
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• 2016

Purpose: The aim of this study was to investigate the effects of grooved abutments on abutment screw loosening. Materials and methods: This study was conducted to evaluate the abutment screw loosening after 6 months for 50 patients (51 implants) treated at the department of Prosthodontics in Yonsei University Dental Hospital from March, 2015 to July, 2015. A control group with non-grooved abutment consists of 30 implants, and an experimental group with grooved abutment consists of 21 implants. Astra, Straumann, Implantium, Osstem system were used in the study. The abutments with loose screws cases after a period of 6 months has been investigated, with two kinds of measurements: 1) measuring the additional rotational angle on abutment during placement with the same force, 2) measuring the PTV on bucco-cervical area of implant crown. All data collected has been analyzed by normality test followed by Mann-Whitney test using SPSS program. Results: No complications were reported after 6 months for the 51 implants. Abutment screw loose and crown fracture have not been seen in the study groups. The data collected from the two measurements showed no significant differences between the two groups with P-value 0.576 (average= control group: $7.35^{\circ}$, experimental group: $4.75^{\circ}$) for the additional rotational angle measurement and with P-value 0.767 for PTV. Conclusion: There are no significant differences between the grooved and non-grooved abutment in screw stability. However, further studies with long-term followups and larger group of patients is needed in order to investigate the effects of grooved abutment on screw stability.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.6
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• pp.664-670
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• 2004

Statement of problem. One of the common problems of dental implant prosthesis is the loosening of the screw that connects each component, and this problem is more common in single implant-supported prostheses with external connection. Purpose. The purpose of this study was to examine the changes of detorque values of abutment screws with external connection in different abutment heights. Materials and methods. After cyclic loading on three different abutment heights, detorque values were measured. Abutments were retained with titanium abutment screws tightened to 30 Ncm (30.5 kgmm) with digital torque gauge as recommended by the manufacturer. Replacing abutments, implants and titanium abutment screws with new ones at every measurement, initial detorque values were measured six times. In measuring de torque values after cyclic loading, Avana Cemented Abutments of 4.0 mm collar, 7.0 mm height (Osstem Co., Ltd., Seoul, Korea) were used with three different lengths of 5.0, 8.0, 11.0 mm. Shorter abutments were made by milling of 11.0 mm abutment to have the same force-exercised area of 4.5 mm diameter. Sine curve force (20N-320N, 14Hz) was applied, and detorque values were measured after cyclic loading of 2 million times by loading machine. Detorque values of initial and after-loading were measured by digital torque gauge. One-way ANOVA was employed to see if there was any influence from different abutment heights. Results. The results were as follows: 1. The initial detorque value was 27.8$\pm$0.93 kgmm, and the ratio of the initial detorque value to the tightening torque was 0.91(27.8/30.5). 2. Measured detorque values after cyclic loading were declined as the height of the abutment increased, that was, 5.0 mm; 22.3$\pm$0.82 kgmm, 8.0 mm; 21.8$\pm$0.93 kgmm, and 11.0 mm; 21.3$\pm$0.94 kgmm. 3. One-way ANOVA showed no statistically significant differences among these (p>0.05). 4. Noticeable mobility at the implant-abutment interface was not observed in any case after cyclic loading at all.

• Journal of Veterinary Clinics
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• v.23 no.3
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• pp.291-299
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• 2006

During long bone lengthening, there are many disadvantages including axial deviation, malalignment and re-fracture which are commonly encountered inspite of its proven abilities. To study the effects of intramedullary K-wire application on the lengthening of long bone, ten skeletally mature mongrel dogs were separated into two groups(Group I, II). Right femurs of group I(5 dogs) were fixed with only monolateral external fixator after subperiosteal osteotomy. Right femurs of group II(5 dogs) were fixed with mono lateral external fixator and intramedullary K-wire after subperiosteal osteotomy. Lengthening was started at 7 days after the surgery with the rate of 0.5 mm per day for 5 weeks and the dogs were sacrificed after 15 weeks postoperatively to examine histologic differences and evaluate bone mineral density. Radiographic examination at an interval of two weeks was done to evaluate the type of callus formed and to analyze complications including instability of external skeletal fixation and axial deviation. Bone mineral density at the lengthened area and contralateral nonlengthened area were measured using quantitative computerized tomography. Histological examination of regenerated bone was performed using Masson's trichrome stain method. The radiographs demonstrated poor callus formation, higher incidence of axial deviation and screw loosening in the group I compared to the group II. The bone mineral density at the lengthened area in the group II was higher than that of the group I(P<0.05). Histological examination showed that the new bone trabeculae in the group II were greater than that of the group I. In conclusion, the combination of monolateral external fixator and intramedullary K-wire can prevent pin loosening, axial deviation and reduce healing period in dogs.

• Journal of the Korean Professional Engineers Association
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• v.39 no.3 s.186
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• pp.32-35
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• 2006

The recent speculation fever in Kangnam have been cooled down by the August 31 heavy taxation tool for curbing speculators. Another March 30 real estate control equipped with high capital gains tax up to 50% was targeting reconstruction projects of dilapidated apartment complexes mostly inside of Kangnam area. The shortage of larger unit supply with its high demand results in price polarization problem. It makes higher price for larger units and less price for smaller units, and therefore higher priced home owners become richer and lower priced home owners become poorer. To avoid the polarization problem and anther probable price hikes in the near future, it may be suggested to supply quality homes by loosening the tight rules for the apartment reconstruction project, and thereby kangnam housing price stabilization can be achieved.