• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.4
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• pp.329-340
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• 2006

Statement of problem: Damping of the peak force transmitted to implants has been reported by in vitro studies using impact forces on resin-veneered superstructures. Theoretical assumptions suggest that use of acrylic resin for the occlusal surfaces of a prosthesis would protect the connection between implant and bone. Therefore, the relationship between prosthesis materials and the force transmitted through the implant system also needs to be investigated under conditions that resemble the intraoral mechanical environment. Purpose: The purpose of this study was to analyze the fracture strength and modes of temporary prosthesis when a flange or occlusally extended structure were connected on the top of the abutment. Material and method: Modified abutments of winged and bulk design were made by casting the desired wax pattern which is made on the UCLA type plastic cylinder. Temporary crowns were made using templates on the modified abutments, and its fracture toughness and strain were compared to the traditional temporary prosthesis. To evaluate the effect of aging, 5.000 times of thermocycling were performed, and their result was compared to the 24hours specimen result. Results: The following conclusions were drawn from this study: 1. In the fracture toughness test, temporary crown's fracture line located next to the screw hole while modified designs with metal support showed fracture line on the metal and its propagation along the metal-resin interface. 2. Wing and bulk structure didn't show significant difference in the fracture toughness (p>0.05), but wing structure showed stress concentration on the screw hole area compared to bulk structure which showed even stress distribution. 3. In the fracture toughness test after thermocycling, wing and bulk structure showed increased or similar results in metal supported area while off-metal area and temporary crown showed decreased results. 4. In the strain measurement after thermocycling, its value increased in the temporary and bulk structure. However, wing structure showed decreased value in the loading point while increased value in the screw hole area. Conclusion: Wing type design showed compatible result to the bulk type that its application with composite resin prosthesis to the implant dentistry is considered promising.

• Journal of Technologic Dentistry
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• v.31 no.1
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• pp.55-61
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• 2009

Passive fitting of meso-structure and super-structures is a predominant requirement for the longevity and clinical success of osseointegrated dental implants. However, precision and passive fitting has been unpredictable with conventional methods of casting as well as for corrective techniques. Alternative to conventional techniques, electro discharge machining(EDM) is an advanced method introduced to dental technology to improve the passive fitting of implant prosthesis. In this technique material is removed by melting and vaporization in electric sparks. Regarding the efficacy of EDM, the application of this technique induces severe surface morphological and elemental alterations due to the high temperatures developed during machining, which vary between $10,000{\sim}20,000^{\circ}C$. The aim of this study was to investigate the morphological and elemental alterations induced by EDM process of casting dental gold alloy and non-precious alloy used for the production of implant-supported prosthesis. A conventional clinical dental casting alloys were used for experimental specimens patterns, which were divided in three groups, high fineness gold alloy(Au 75%, HG group), low fineness gold alloy(Au 55%, LG group) and nonprecious metal alloy(Ni-Cr, NP group). The UCLA type plastic abutment patterns were invested with conventional investment material and were cast in a centrifugal casting machine. Castings were sandblasted with $50{\mu}m\;Al_2O_3$. One casting specimen of each group was polished by conventional finishing(HGCON, LGCON, NPCON) and one specimen of each group was subjected to EDM in a system using Cu electrodes, kerosene as dielectric fluid in 10 min for gold alloy and 20 min for Ni-Cr alloy(HGEDM. LGEDM, NOEDM). The surface morphology of all specimens was studied under an energy dispersive X-ray spectrometer (EDS). The quantitative results from EDS analysis are presented on the HGEDM and LGEDM specimens a significant increase in C and Cu concentrations was found after EDM finishing. The different result was documented for C on the NPEDM with a significant uptake of O after EDM finishing, whereas Al, Si showed a significant decrease in their concentrations. EDS analysis showed a serious uptake of C and Cu after the EDM procedure in the alloys studied. The C uptake after the EDM process is a common finding and it is attributed to the decomposition of the dielectric fluid in the plasma column, probably due to the development of extremely high temperatures. The Cu uptake is readily explained from the decomposition of Cu electrodes, something which is also a common finding after the EDM procedure. However, all the aforementioned mechanisms require further research. The clinical implication of these findings is related with the biological and corrosion resistance of surfaces prepared by the EDM process.

• Journal of the Korean Geotechnical Society
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• v.28 no.1
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• pp.67-77
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• 2012

In this study, a series of centrifuge shaking-table tests for a $3{\times}3$ group pile and a single pile applied by sinusoidal wave was performed in dry sand for various pile spacings, ranging from three to seven times the pile diameter. A comparison of centrifuge tests of both single pile and group pile showed that the lateral ground response of the group pile was smaller than that of the single pile. In addition, the reduction in subgrade reaction for the group pile increased with decreasing pile spacing. The side piles, that is, the 1st row and 3rd row piles showed identical dynamic p-y behavior and the center pile in the 2nd row caused a lower reduction effect compared with the 1st and 3rd row piles. From the comparison between the p-y curves of the 2nd row piles, it was found that the lateral ground response of the outer pile in the 2nd row was less than that of the center pile in the 2nd row. The p-multipliers for the side piles, for the center pile and for the outer pile ranged from 0.28 to 0.77, from 0.55 to 1.0 and from 0.39 to 0.87, respectively.

• Clinics in Shoulder and Elbow
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• v.1 no.1
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• pp.109-117
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• 1998

We evaluated the results of the surgery for impingement syndromes and partial thickness tears of the rotator cuff with an average follow-up period of 15 months. One group(group I) of 43 patients, 46 cases underwent arthroscopic subacromial decompression. The other comparable group(group Ⅱ) of 10 patients, II cases underwent open acromioplasty. The average age at operation was 48 years, old. Arthroscopic subacromial decompression achieved slightly better pain relief, the range of the acti ve forward flexion, function, strength and the overall score with improvement from the preoperative condition than open acromioplasty. The patient's satisfaction was better in group I as well. Using the UCLA Shoulder Rating Scale, 89% of group I and 82% of group n had good or excellent results. Preservation of the origin of the deltoid during an arthroscopic acromioplasty reduced the postoperative morbidity and made it possible to start rehabilitation sooner and to achieve the better and more predictable results.

• Clinics in Shoulder and Elbow
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• v.3 no.2
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• pp.75-78
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• 2000

Purpose: The purpose of this study was to review primary traumatic anterior shoulder dislocation in the 40 years and older to determine the incidence of recurrence, rotator cuff injury and associated fractures. Materials and Methods: From May, 1991 to October, 1998, seventeen patients were available to participate in the study. The average age was 55 years(range, 40 to 75 years). Follow-up averaged 27 months(range, 12 to 48 months). There were 12 men and 5 women. 10 right and 7 left shoulders were involved. Any participant with a history of shoulder pain and limitation of motion was excluded from the study. Each shoulder was evaluated with UCLA shoulder functional assessment. Results: The overall results were excellent in 9 patients(52.9%), good in 3 patients(17 .6%), fair in 3 patients(17.6%), and poor in 2 patients(11.7%). Surgical treatment of the associated rotator cuff and greater tuberosity fracture injuries resulted in 5 patients with excellent(55.6%), 3 patients with good(33.3%) and I patient with poor(11.1 %) and Nonsurgical treatment of the associated injuries resulted in 2 patients with excellent(33.3%), 3 patients with fair(50%), 1 patient with poor(16.7%)(P=0.025). Conclusion : Our findings on small number of patients suggest that the diagnosis of a rotator cuff and other pathologies should be approached aggressively by an MRI, CT arthrogram if significant pain and weakness are still present and early surgical repair of rotator cuff and greater tuberosity can lead to restoration of shoulder function and better outcomes in selected patients.

• Clinics in Shoulder and Elbow
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• v.14 no.2
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• pp.236-241
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• 2011

Purpose: To report the usefulness of dynamic ultrasonography in subluxation of the long head of the biceps tendon, which is difficult to detect with static imaging such as plain radiography, static sonography, MRI and in a subtle physical examination. Materials and Methods: Two male patients suffered from subluxation of the long head of the biceps. This difficult diagnosis? was managed by surgery (biceps soft tissue tenodesis) with the aid of dynamic ultrasonography. At final follow up, we evaluated patients' symptoms and functional outcomes using KSS, UCLA and ASES scores. Results: We diagnosed and treated subluxation of the long head of the biceps easily using dynamic ultrasonography. At the final follow up, both patients' symptoms and functional outcomes were improved. There were no significant complications. Conclusion: Dynamic ultrasonography is a useful method in the difficult and subtle diagnosis of subluxation of the long head of the biceps.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.595-602
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• 2006

An experimental study was conducted to investigate seismic behaviour of post-tensioned(PT) exterior slab-column connections used for the purpose to resist gravity loads only. For these, 2/3-scale, two PT post-tensioned exterior connections with two different tendon arrangement patterns and one conventional reinforced concrete(RC) exterior connection was tested under quasi-static, uni-directional reversed cyclic loading. During the lateral testing, gravity forces transferred to the column were kept constant to closely simulate a moment to shear ratio of a real building. One of the objectives of this study was to assess the necessity and/or the quantity of bottom bonded reinforcement needed to resist moment reversal which would occur under significant inelastic deformations of the adjacent lateral force resisting systems. The ACI 318 and 352 provisions for structural integrity were applied to provide the bottom reinforcement passing through the column for the specimens. Prior test results were also collected to conduct comparative studies for some design parameters such as the tendon arrangement pattern, the effect of post-tensioning forces and the use of bottom bonded reinforcement. Consequently, the impact of tendon arrangement on the seismic performance of the PT connection, that is lateral drift capacity and ductility, dissipated energy and failure mechanism, was considerable. Moreover, test results showed that the amount of bottom reinforcement specified by ACI 352. 1R-89 was sufficient for resisting positive moments arising from moment reversal under reversed cyclic loads. Shear strength of the tested specimens was more accurately predicted by the shear strength equation(ACI 318) considering the average compressive stress over the concrete($f_{pc}$) due to post-tensioning forces than that without considering $f_{pc}$.

• Journal of the Korean Geotechnical Society
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• v.27 no.9
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• pp.87-98
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• 2011

In this study, the magnitude and phase variation of dynamic earth pressure acting on a pile in liquefiable soils were analyzed using a series of 1g shaking table tests. In the case of a pile in dry sand, the value of the dynamic earth pressure was the highest near the surface due to the inertia force of the upper load on the pile and it decreased as the depth of the pile got lower. On the other hand, for a pile in liquefiable sand, the magnitude and shape of the dynamic earth pressure were similar to those of the excess pore pressure and was largely affected by the deformation of soils. Furthermore, the inertia force of the upper load and the dynamic earth pressure acted in opposite directions in cases of dry sand and saturated sand where low excess pore pressure had developed. However, after liquefaction, those force components near surface acted unfavorably in the same direction. Finally, the Westergaard’s solution was modified and proposed as a method to evaluate the magnitude of dynamic earth pressure acting on a pile during liquefaction.

• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.4
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• pp.257-268
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• 2003

The purpose of this study was to assess the loading distributing characteristics of implant prosthesis according to position and direction of load, under vertical and inclined loading using FEA analysis. The finite element model was designed according to standard fixture (4.1mm restorative component x 11.5mm length). The crown for mandibular first molar was made using UCLA abutment. Each three-dimensional finite element model was created with the physical properties of the implant and surrounding bone. This study simulated loads of 200N at the central fossa in a vertical direction (loading condition A), 200N at the outside point of the central fossa with resin filling into screw hole in a vertical direction (loading condition B), 200N at the centric usp in a $15^{\circ}$ inward oblique direction (loading condition C), 200N at the in a $30^{\circ}$ inward oblique direction (loading condition D) or 200N at the centric cusp in a $30^{\circ}$ outward oblique direction (loading condition E) individually. Von Mises stresses were recorded and compared in the supporting bone, fixture, and abutment screw. The following results have been made based on this study: 1. Stresses were concentrated mainly at the ridge crest around implant in both vertical and oblique loading but stresses in the cancellous bone were low in both vertical and oblique loading. 2. Bending moments resulting from non-axial loading of dental implants caused stress concentrations on cortical bone. The magnitude of the stress was greater with the oblique loading than with the vertical loading. 3. An offset of the vertical occlusal force in the buccolingual direction relative to the implant axis gave rise to increased bending of the implant. 4. The relative positions of the resultant line of force from occlusal contact and the center of rotation seems to be more important. 5. The magnitude of the stress in the supporting bone, fixture and abutment screw was greater with the outward oblique loading than with the inward oblique loading and was the greatest under loading at the centric cusp in a $30^{\circ}$ outward oblique direction. Conclusively, this study provides evidence that bending moments resulting from non-axial loading of dental implants caused stress concentrations on cortical bone. But it seems to be more important that how long is the distance from center of rotation of the implant itself to the resultant line of force from occlusal contact(leverage). The goal of improving implants should be to avoid bending of the implant.

• Journal of the Korean GEO-environmental Society
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• v.10 no.7
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• pp.103-109
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• 2009

The probabilistic seismic hazard analysis (PSHA) calculates the probability of exceedance of a certain ground motion parameter within a finite period at a site of interest. PSHA is very robust in that it can account for the uncertainties in seismic source, wave passage effect, and seismic site effects and hence, it is the most widely used method in quantifying the future earthquake induced ground vibration. This paper evaluates the applicability of a new PSHA that is alleged to be able to reproduce the results of a conventional PSHA method, but generates a series of earthquake scenarios and corresponding ground motion time histories that are compatible with the scenarios. In the application, a 40,000 year period is simulated, during which 16,738 virtual earthquakes have occurred. The seismic hazard maps are generated from the outputs of the new PSHA. Comparisons with the maps generated by the conventional PSHA method demonstrated that the new PSHA can successfully reproduce the results of a conventional PSHA. The new PSHA may not be very meaningful in itself. However, the real advantage of the method is that it can be used to develop probabilisitic seismic site coefficients. The suite of generated ground motion time histories are used to develop probabilistic site coefficients in the companion paper.