• Journal of Dental Rehabilitation and Applied Science
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• v.21 no.1
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• pp.1-14
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• 2005

The purpose of this study was to assess the loading distributing characteristics of implant prosthesis of internal connection system(ITI system) according to position and direction of load, under vertical and inclined loading using finite element analysis (FEA). The finite element model of a synOcta implant and a solid abutment with $8^{\circ}$ internal conical joint used by the ITI implant was constructed. The gold crown for mandibular first molar was made on solid 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 cusp 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. The following results have been made based on this study: 1. Stresses were concentrated mainly at the ridge crest around implant under both vertical and oblique loading but stresses in the cancellous bone were low under 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. So, the relative positions of the resultant line of force from occlusal contact and the center of rotation seems to be more important. 4. In this internal conical joint, vertical and oblique loads were resisted mainly by the implant-abutment joint at the screw level and by the implant collar. Conclusively, It seems to be more important that how long the distance is from center of rotation of the implant itself to the resultant line of force from occlusal contact (leverage). In a morse taper implant, vertical and oblique loads are resisted mainly by the implant-abutment joint at the screw level and by the implant collar. This type of implant-abutment connection can also distribute forces deeper within the implant and shield the retention screw from excessive loading. Lateral forces are transmitted directly to the walls of the implant and the implant abutment mating bevels, providing greater resistance to interface opening.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.5
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• pp.653-664
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• 2007

Statement of problem: The screw detorque value is a measure of the preload remaining in the screw just before detorquing. Purpose: This study evaluated the effect of different screw tightening sequences and tightening methods on detorque values for a well-fitting implant superstructure. Material and method: An implant superstructure that connected directly to four implants (Astra Tech) was fabricated on a fully edentulous mandibular acrylic resin model. Six well-fitting dental stone casts were made with a pickup impression of the superstructure from the acrylic resin model. To evaluate the effect of three screw tightening sequences (1-2-3-4, 2-4-3-1, and 2-3-1-4) and two tightening methods (2-step and 1-step) on the stability of screw joint, the detorque values for a well-fitting implant superstructure were measured twice after screw tightening using 20 Ncm. Detorque values were analyzed using multi-way analysis of variance and two-way analysis of variance at a .05 level of significance. Results: 1. The mean detorque values for three screw tightening sequences were 12.3 Ncm, 12.6 Ncm, and 12.0 Ncm, respectively. 2. The mean detorque values for two screw tightening methods were 12.0 Ncm, and 12.2 Ncm, respectively. 3. The mean of mimimum detorque values for three screw tightening sequences and for two tightening methods were 10.6 Ncm, 11.1 Ncm, 10.5 Ncm, and 9.8 Ncm, respectively. 4. No statistically significant differences among the variables of screw tightening sequence and tightening method were found (p>.05) for detorque values and for mimimum detorque values. Conclusion: Within the limitations of this study, the screw tightening sequence and tightening method did not have a significant effect on the detorque values for a well-fitting implant superstructure.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.9
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• pp.188-195
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• 2004

Severe osteoarthrosis of the knee joint often requires total knee arthroplasty(TKA) to yield adequate knee function. The knee joint with TKA is expected ideally to restore the characteristics, however, this is not necessarily 1.ue in the clinical cases. In this study the motion of the intact joint and the joint after. TKA were investigated numerically using computer simulation. For active knee extension from 90 degrees of flexion to full extension, the intact knee joint exhibited anterior tibial translation near the full extension and it showed only rotation at other flexion angles. Physiologic external rotation of the tibia near full extension known as screw home movement was also noted in the analytical model. The analysis of the tibial insert of three different shapes (flat, semicurved, and curved types) demonstrated characteristic rotational and sliding motion as well as different contact forces.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.458-461
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• 1997

We have developed a human-sized BWR(biped walking robot) driven by a new actuator based on the ball screw which has high strength and high gar ratio. Each leg of the robot is composed of three pitch joints and one roll joint. In all, a 10 degree-of-freedom robot with two balancing joints was developed. For the purpose of autonomous walking and higher performance, we improved the previous developed BWR. We improved the motor drive efficiency, designed the ball screw actuator in a modular type, and simplified the electric wires. Through this modification, we achieved better performance in walking.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.6
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• pp.484-491
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• 2002

We developed a new type of human-sized BWR (biped walking robot) driven by a new actuator based on the ball screw which has high strength and high gear ratio. Each leg of the robot is composed of three pitch joints and one roll joint. In all, a 10 degree-of-freedom robot with two balancing joints was developed. A new type of actuator for the robot is proposed, which is composed of four bar link mechanism driven by the ball screw. The robot overcomes the limit of the driving torque of conventional BWRs. The BWR was designed to walk autonomously by adapting small DC motors for the robot actuators and has a space to board DC battery and controllers. In the performance test, the BWR performed sitting-up and down motion, and walking motion. Through the test, we found the possibility of a high performance biped-walking.

• Journal of Korean Neurosurgical Society
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• v.55 no.5
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• pp.255-260
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• 2014

Objective : The purpose of this study was to compare the radiological and neurological outcomes between two atlantoaxial fusion method for atlantoaxial stabilization; C1 lateral mass-C2 pedicle screws (screw-rod constructs, SRC) versus C1-2 transarticular screws (TAS). Methods : Forty-one patients in whom atlantoaxial instability was treated with atlantoaxial fixation by SRC group (27 patients, from March 2005 to May 2011) or TAS group (14 patients, from May 2000 to December 2005) were retrospectively reviewed. Numeric rating scale (NRS) for pain assessment, Oswestry disability index (ODI), and Frankel grade were also checked for neurological outcome. In radiologic outcome assessment, proper screw position and fusion rate were checked. Perioperative parameters such as blood loss during operation, operation time, and radiation exposure time were also reviewed. Results : The improvement of NRS and ODI were not different between both groups significantly. Good to excellent response in Frankel grade is shown similarly in both groups. Proper screw position and fusion rate were also observed similarly between two groups. Total bleeding amount during operation is lesser in SRC group than TAS group, but not significantly (p=0.06). Operation time and X-ray exposure time were shorter in SRC group than in TAS group (all p<0.001). Conclusion : Both TAS and SRC could be selected as safe and effective treatment options for C1-2 instability. But the perioperative result, which is technical demanding and X-ray exposure might be expected better in SRC group compared to TAS group.

• Journal of Korean Foot and Ankle Society
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• v.17 no.4
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• pp.264-271
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• 2013

Purpose: We aimed to analyze the effect of fixation tightness of the syndesmotic screw and its indwelling period on the recurrence of the syndesmosis widening after screw removal and the clinical outcomes. Materials and Methods: Forty consecutive patients with acute syndesmotic injury were retrospectively reviewed. The tibiofibular clear space is measured by digitalized measurement tool on serial radiographs. We analyzed the effect of time from trauma to fixation, syndesmotic screw indwelling duration, and fixation methods. Residual symptoms at the last follow up were evaluated. The student t-test, correlation test, and chi-square test were used for statistical analysis. Results: Eighteen ankles (45%) had recurrent syndesmosis widening (greater than 5% compared to the contralateral side). Seven patients had pain and five had limitation of motion in the ankle joint. Fixation tightness had significant effect on reducing the recurrence while the severity of the initial widening, time to fixation, and duration of fixation did not affect the outcome. Conclusion: Tight fixation of syndesmotic screw is essential for achieving final syndesmotic stability and reducing recurrence.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.2
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• pp.97-109
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• 2010

Purpose : This study was designed to evaluate the influence of implant abutment materials on detorque value and screw joint stability before and after dynamic fatigue test. Materials & Methods : The external hexagonal fixture and three different groups of abutment (titanium abutments, zirconia abutments, and UCLA abutments) were used. The detorque value before loading and after loading (cyclic loading up to $10^5$ cycles) of the abutment screw were measured. Result : 1. There was no significant difference in detorque value before loading among the each group. 2. There was no significant difference in detorque value after loading among the each group. 3. Detorque values before and after cyclic loading in each group were not significantly different. 4. There was no significant difference in loss percentage of removal torque before loading among the each group. 5. There was no significant difference in loss percentage of removal torque after loading among the each group. 6. There was no significant difference in loss percentage of removal torque according to loading among the each group. Conclusion : Short term screw loosening of three types of abutment was not significantly different. When bite force was applied, there was no significant difference in screw loosening between before loading and after loading.

• Journal of Korean Neurosurgical Society
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• v.61 no.2
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• pp.277-281
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• 2018

Objective : Craniovertebral junctional anomalies constitute a technical challenge. Surgical opening of atlantoaxial joint region is a complex procedure especially in patients with nuchal deformity like basilar invagination. This region has actually very complicated anatomical and functional characteristics, including multiple joints providing extension, flexion, and wide rotation. In fact, it is also a bottleneck region where bones, neural structures, and blood vessels are located. Stabilization surgery regarding this region should consider the fact that the area exposes excessive and life-long stress due to complex movements and human posture. Therefore, all options should be considered for surgical stabilization, and they could be interchanged during the surgery, if required. Methods : A 53-year-old male patient applied to outpatients' clinic with complaints of head and neck pain persisting for a long time. Physical examination was normal except increased deep tendon reflexes. The patient was on long-term corticosteroid due to an allergic disease. Magnetic resonance imaging and computed tomography findings indicated basilar invagination and atlantoaxial dislocation.The patient underwent C0-C3-C4 (lateral mass) and additional C0-C2 (translaminar) stabilization surgery. Results : In routine practice, the sites where rods are bound to occipital plates were placed as paramedian. Instead, we inserted lateral mass screw to the sites where occipital screws were inserted on the occipital plate, thereby creating a site where extra rod could be bound.When C2 translaminar screw is inserted, screw caps remain on the median plane, which makes them difficult to bind to contralateral system. These bind directly to occipital plate without any connection from this region to the contralateral system.Advantages of this technique include easy insertion of C2 translaminar screws, presence of increased screw sizes, and exclusion of pullout forces onto the screw from neck movements. Another advantage of the technique is the median placement of the rod; i.e., thick part of the occipital bone is in alignment with axial loading. Conclusion : We believe that this technique, which could be easily performed as adjuvant to classical stabilization surgery with no need for special screw and rod, may improve distraction force in patients with low bone density.

• Journal of Korean Foot and Ankle Society
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• v.24 no.3
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• pp.107-112
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• 2020

Purpose: Hallux valgus (HV) is a common foot deformity that causes pain in the first metatarsophalangeal joint. Distal metatarsal osteotomies are commonly performed as a treatment. This retrospective study compared the clinical and radiological results of bioabsorbable magnesium (Mg) versus titanium (Ti) screw fixation for modified distal chevron osteotomy in HV. Materials and Methods: Forty-nine patients, who underwent modified distal chevron osteotomy for HV in 2018 and 2019, were reviewed retrospectively. Bioabsorbable Mg screw fixation was applied in 20 patients (22 feet), and a traditional Ti compression screw was applied in 29 patients (40 feet). The patients were followed up for at least six months. The clinical results were evaluated using the American Orthopaedic Foot and Ankle Society hallux metatarsophalangeal-interphalangeal (AOFAS-MTP-IP) scale and a visual analogue scale (VAS). The hallux valgus angle (HVA), intermetatarsal angle (IMA), and distal metatarsal articular angle (DMAA) were measured before, after surgery, and at the six months follow-up. Results: The AOFAS-MTP-IP scale and VAS points were improved in both groups, with no significant difference between them. At the six-month follow-up, HVA, IMA, and DMAA were similar. Bone union was confirmed in both groups, and there were no significant major complications in both groups. Four people in the Ti screw group underwent implant removal surgery. Conclusion: Bioabsorbable Mg screws showed comparable clinical, radiologic results to Ti standard screws six months after distal modified chevron osteotomy. These screws are an alternative fixation material that can be used safely and avoid the need for implant removal operations.