• Journal of Dental Rehabilitation and Applied Science
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• v.18 no.4
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• pp.321-329
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• 2002

Bending moments results from offset overloading of dental implant, which may cause stress concentrations to exceed the physiological capacity of cortical bone and lead to various kinds of mechanical failures. The purpose of this study was to compare the distributing pattern of stress on the finite element models with the different angulated placement of dental implant in mandibular posterior missing areas. The three kinds of finite element model, were designed according to 3 main configurations: Model 1(parallel typed placement of 2 fixtures), Model 2(15. distal angulated placement of one fixture on second molar area), Model 3(15. mesial angulated placement of one fixture on second molar area). The cemented crowns for mandibular first and second molars were made on the two fixtures (4mm 11.5). Three-dimensional finite element models by two fixtures were constructed with the components of the implant and surrounding bone. A 200N vertical static load were applied to the center of central fossa and the point 2mm apart from the center of central fossa on each model. The preprocessing, solving and postprocessing procedures were done by using FEM analysis software NISA/DISPLAY IV Version 10.0((Engineering Mechanics Research Corporation, USA). Von Mises stresses were evaluated and compared in the supporting bone, fixtures, and abutment. The results were as following : (1) Under the point loading at the central fossa, the direction of angulated fixture affected the stress pattern of implants. (2) Under the offset loading, the position of loading affected more on the stress concentration of implants compare to the angulated direction of implants. The results had a tendency to increase the stress on the supporting bone, fixture and screw under the offset loads when the placement angulation of implant fixture is placed toward mesial or distal direction. In designing of the occlusal scheme for angulated placement, placing the occlusal contacts axially during chewing appears to have advantages in a biomechanical viewpoint.

• Journal of IKEEE
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• v.18 no.2
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• pp.240-247
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• 2014

Intraocular pressure is measured after a cornea air puff by observing biomechanical properties such as thickness or displacement of the cornea. In this paper, we deal with a frequency domain analysis of corneal deformation in the air puff tonometry that is used to diagnose glaucoma or lasik. We distinguish the patient from the normal by measuring the oscillation frequency in the neighborhood of the central cornea section. A binary image was obtained from the video images, and cornea vertical oscillation profile was extracted from the difference between the vertical displacement data and the curve fitting. In terms of Fourier transform, a vibration frequency of 479.2Hz for the patient was obtained as well as more higher 702.8Hz for the normal due to stiffness. Hilbert-Huang transform's empirical mode decomposition generally describes local, nonlinear, and nonstationary data. After the data were decomposed into intrinsic mode functions, a spectrum and power were analysed. Finally, we confirm that the patient has 6 times more higher power ratio for the specific intrinsic mode function between the patient and the normal.

• Journal of the Ergonomics Society of Korea
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• v.30 no.3
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• pp.395-401
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• 2011

Objective: This study examined the effects of working chair that was developed for farmers who work in grapevine's cluster thinning. Background: Agricultural work involves some of the nation's highest occupational risk exposures. Fruit cultivation has been recognized as one of the most hazardous crops in which to work. Grapevine cluster thinning task involve activities related to the main risk factors associated with upper limb work-related musculoskeletal disorders. Method: An experiment was designed to test the working chair. Six healthy male($25.8{\pm}4.9years$) were selected as the subjects for this study. Electromyography(EMG) was used to monitor the muscles activity, and Electro-goniometer was used to measure the ranges of motions of the elbow, trunk and knee. Subjective test was also carried out to examine discomfort body parts and their pain intensity. A grapevine's working space was built for the experiment and working chair was installed on it. In order to examine the muscle activity and range of motion, subjects used to the working chair for 30 minutes for each experimental condition. Another test without working chair was also performed for comparison. %MVC was used to quantify the level of muscle activity. Results: Decreases of muscle activity was found in all leg muscles and significant decrease of muscle activity was found in left Gastrocnemius. The range of motion of the trunk and knee also decreased when working chair used. Discomfort in lower back, thigh and shank region were reduced significantly. However, in upper limbs muscle activity tended to increase in working chair compared with conventional task. Conclusion: Improvement for cushion in seat back and pan required to reduce discomfort in buttocks. Application: Overall findings verified that the working chair might help to prevent upper limb and lower back MSDs based on the current study. These results can be practically used for work improvement for the grapevine growers to prevent MSDs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1243-1248
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• 2011

The purposes of this study were to develop a dynamic model of a human and to investigate the effect of a walker on an elderly subject's motions, such as sit-to-stand (STS) motion and normal gait, by using this model. A human model consisting of 15 segments and 14 joints was developed, embedded in $RecurDyn^{TM}$, and connected through a Simulink$^{(R)}$ interface with collected motion data. The model was validated by comparisons between joint kinematic results from inverse dynamics (Matlab$^{(R)}$-based in-house program) and from $RecurDyn^{TM}$ simulation during walking. The results indicate that the elderly walker induced a longer movement time in walking, such that the speed of joint flexion/extension was slower than that during a normal gait. The results showed that the muscle activities of parts of the ankle and hamstring were altered by use of the elderly walker. The technique used in this study could be very helpful in applications to biomechanical fields.

• Journal of the Korea Safety Management & Science
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• v.4 no.2
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• pp.11-22
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• 2002

In this study, an asymmetric lifting posture prediction model was developed, which was a three-dimensional model with 12 links and 23 degrees of freedom open kinematic chains. Although previous researchers have proposed biomechanical, psychophysical, or physiological measures as cost functions, for solving redundancy, they lack in accuracy in predicting actual lifting postures and most of them are confined to the two-dimensional model. To develop an asymmetric lifting posture prediction model, we used the resolved motion method for accurately simulating the lifting motion in a reasonable time. Furthermore, in solving the redundant problem of the human posture prediction, a moment weighted Joint Range Availability (JRA) was used as a cost function in order to consider dynamic lifting. However, it is known that the moment weighted JRA as a cost function predicted the lower extremity and L5/S1 joint motions better than the upper extremities, while the constant weighted JRA as a cost function predicted the latter better than the former. To compensate for this, we proposed a hybrid moment weighted JRA as a new cost function with moment weighted for only the lower extremity. In order to validate the proposed cost function, the predicted and real lifting postures for various lifting conditions were compared by using the root mean square(RMS) error. This hybrid JRA reduced RMS more than the previous cost functions. Therefore, it is concluded that the cost function of a hybrid moment weighted JRA can be used to predict three-dimensional lifting postures. To compare with the predicted trajectories and the real lifting movements, graphical validations were performed. The results also showed that the hybrid moment weighted cost function model was found to have generated the postures more similar to the real movements.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.31 no.2
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• pp.116-126
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• 2009

The use of short implants has been accepted risky from biomechanical point of view. However, short implants appear to be a long term viable solution according to recent clinical reports. The purpose of this study was to investigate the effect of different diameter and length of implant size to the different type of bone on the load distribution pattern. Stress analysis was performed using 3-dimensional finite element analysis(3D-FEA). A three-dimensional linear elastic model was generated. All implants modeled were of the various diameter(${\phi}4.0$, 4.5, 5.0 and 6.0 mm) and varied in length, at 7.0, 8.5 and 10.0 mm. Each implant was modeled with a titanium abutment screw and abutment. The implants were seated in a supporting D2 and D4 bone structure consisting of cortical and cancellous bone. An amount of 100 N occlusal load of vertical and $30^{\circ}$ angle to axis of implant and to buccolingual plane were applied. As a result, the maximum equivalent stress of D2 and D4 bones has been concentrated upper region of cortical bone. As the width of implant is increased, the equivalent stress is decreased in cancellous bone and stress was more homogeneously distributed along the implants in all types of bone. The short implant of diameter 5.0mm, 6.0mm showed effective stress distribution in D2 and D4 bone. The oblique force of 100N generated more concentrated stress on the D2 cortical bone. Within the limitations of this study, the use of short implant may offer a predictable treatment method in the vertically restricted sites.

• Journal of Korean Dental Science
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• v.4 no.2
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• pp.52-58
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• 2011

Purpose: Modifications of implant design have been related to improving initial stability. The purpose of this study was to investigate their respective effect on initial stability between two tapered implant systems (self-tapping vs. non-self-tapping) in medium density bone using three different analytic methods. Materials and Methods: Self-tapping implant (GS III$^{(R)}$; Osstem Implant Co., Busan, Korea) and non-self-tapping implant (Replace Select$^{(R)}$; Nobel Biocare, G$\H{o}$teborg, Sweden) were investigated. In Solid rigid polyurethane blocks of artificially simulated Quality 2 bone, each of the 5 implants was inserted according to the manufacturer's instructions for medium-bone drilling protocol. Evaluation of initial stability was carried out by recording the maximum insertion torque (IT) and performing the resonance frequency analysis (RFA), and the pull-out test. Results: The IT and RFA values of self-tapping implant were significantly higher than those of non self-tapping implant (P=.009 and P=.047, respectively). In the pull-out values, no significant differences were found in implants between two groups (P=.117). Within each implant system, no statistically significant correlation was found among three different outcome variables. Conclusions: These findings suggest that design characteristics of implant geometry significantly influence the initial stability in medium bone density.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.23 no.1
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• pp.27-33
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• 2014

The patient was a 26-year old female who was not satisfied with the aesthetic approach of her maxillary incisors. The treatment goal throughout the process was to manage the risk and recreate the original and youthful appearance of the smile. The biomechanical risk was managed by providing coverage of the exposed dentin and rebuilding the eroded structures with minimal tooth reduction throughout the treatment. Functional risk and prognosis for this patient were both improved by achieving acceptable function. The patient was satisfied with the full-ceramic restorations and the symmetry, harmony gingival architecture.

• Journal of Periodontal and Implant Science
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• v.28 no.3
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• pp.401-408
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• 1998

Screw shaped implants of Titanium-13Zirconium-6Niobium(newly developed), Titanium-6Zirconium-6Sn-6Niobium(newly developed) and Titanium-6Aluminum-4Vanadium were machined with square top and inserted in rabbit bone for 3 months. Biomechanical tests(removal torque) showed Titanium-13Zirconium-6Niobium and Titanium-6Zirconium-6Sn-6Niobium to be more stable in the bone bed than those of Titanium-6Aluminum-4Vanadium. Titanium-13Zirconium-6Niobium implants demonstrated a mean removal torque of 31.59Ncm while Titanium-6Aluminum-4Vanadium demonstrated a mean removal torque of 25.27Ncm and Titanium-6Zirconium-6Sn-6Niobium revealed a mean removal torque of 37.44Ncm and were statistically significance in Wilcoxon Signed Rank test(P<0.05). Histomorphometrical comparisons were performed on $10\;{\mu}m$ thick undecalcified ground sections in the light microscope and Titanium-13Zirconium-6Niobium showed more mean bone-tometal contact ratio than to other twotitanium alloys but had no statistically significant differences were found among the three materials(P>0.01).

• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.3
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• pp.239-245
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• 2003

The occurrence and pattern of tooth wear are related to cultural, dietary, occupational, and geographic factors, Excessive occlusal wear can result in pulpal exposure, occlusal disharmony, functional inability. Surface loss can be differentiated into 3 general causal categories: i) mechanical loss, which includes attrition, ii) abrasion chemical loss including erosion, and finally iii) a proposed biomechanical category described as abfraction. Considering that mechanical wear is frequently asymptomatic, patients may have parafunctional habit. Structured clinical decision analysis in fixed prosthodontics, as other branches of dentistry do, allows the practitioner to consider the patient's problems more thoroughly based on the clinical data and extenuation factors. This discipline of decision making is intended to complement the experience level and educational background of the clinician in assisting the patient through the decision process. Additionally, CDA helps the clinician define not only the pre-existing condition of the patient prior to irreversible therapy, but also better treatment strategies for the patient over an extended period. The systematic nature of decision analysis stimulates the dentists to pay further attention to those factors, which is germane to the overall complexity of the case, and exclude factors, which have little influence on its final outcome. Further implementation of computerized databases, procedural outcome probabilities based on clinical and laboratory studies and the clinical experience of those who use it, may provide quite a promising future in the field of structured and formalized clinical decision analysis.