• Journal of Dental Rehabilitation and Applied Science
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• v.40 no.1
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• pp.24-30
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• 2024

Complicated crown fractures of maxillary anterior teeth caused by trauma in adolescence can cause functional and aesthetic problems. For crown fractures with pulp exposure, various restorative methods can be considered depending on the amount of remaining tooth structure. Direct resin restorations are the most traditional and effective method, but they are likely to discolor and break over time. Fixed prosthesis have a high possibility of re-restoration due to marginal disharmony due to tooth movement during the growth period, and restorations using post which are mainly performed for extensive crown fractures increase the risk of root perforation and root fracture. However, endocrown is an integrated structure that gains retention force from the pulp space, enabling effective reconstruction from a biomechanical perspective and providing advantages in restoring function and aesthetics. Therefore, endocrown can be considered as a restoration method for complicated crown fractures caused by trauma in adolescence.

• The korean journal of orthodontics
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• v.41 no.5
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• pp.354-360
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• 2011

Objective: To investigate the effects of different pilot-drilling methods on the biomechanical stability of self-tapping mini-implant systems at the time of placement in and removal from artificial bone blocks. Methods: Two types of artificial bone blocks (2-mm and 4-mm, 102-pounds per cubic foot [102-PCF] polyurethane foam layered over 100-mm, 40-PCF polyurethane foam) were custom-fabricated. Eight mini-implants were placed using the conventional motor-driven pilot-drilling method and another 8 mini-implants were placed using a novel manual pilot-drilling method (using a manual drill) within each of the 2-mm and 4-mm layered blocks. The maximum torque values at insertion and removal of the mini-implants were measured, and the total energy was calculated. The data were statistically analyzed using linear regression analysis. Results: The maximum insertion torque was similar regardless of block thickness or pilot-drilling method. Regardless of the pilot-drilling method, the maximum removal torque for the 4-mm block was statistically higher than that for the 2-mm block. For a given block, the total energy at both insertion and removal of the mini-implant for the manual pilot-drilling method were statistically higher than those for the motor-driven pilot-drilling method. Further, the total energies at removal for the 2-mm block was higher than that for the 4-mm block, but the energies at insertion were not influenced by the type of bone blocks. Conclusions: During the insertion and removal of mini-implants in artificial bone blocks, the effect of the manual pilot-drilling method on energy usage was similar to that of the conventional, motor-driven pilot-drilling method.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.18 no.3
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• pp.239-247
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• 2008

Low back disorders (LBDs) have been the most common musculoskeletal problem in Korean workplaces. It affects many workers, and is associated with high costs to many companies as well as the individual, which can negatively influence even the quality of life of workers. The _evaluation of low back disorder risk associated with manual materials handling tasks can be performed using variety of ergonomic assessment tools such as National Institute for Occupational Safety and Health (NIOSH) Revised Lifting Equation (NLE), the Washington Administrative Code 296-62-0517 (WAC), the Snook Tables etc. But most of these tools provide limited information for choosing the most appropriate assessment method for a particular job and in finding out advantage and disadvantage of the methods, and few have been assessed for their predictive ability. The focus of this study was to _evaluate spinal loads in real time with lifting and pulling heavy cow leathers in variety of postures. Data for estimating mean trunk motions were collected as employees did their work at the job site, using the Lumbar Motion Monitor. Eight employees (2 males, 6 females) were selected in this study, in which the load weight and the vertical start and destination heights of the activity remained constant throughout the task. Variance components (three dimensional spaces) of mean trunk kinematic measures were estimated in a hierarchical design. They were used to compute velocity and acceleration of multiple employees performing the same task and to repetitive movements within a task. Therefore, a results of this study could be used as a quantitative, objective measure to design the workplace so that the risk of occupationally related low back disorder should be minimized.

• Korean Journal of Applied Biomechanics
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• v.14 no.3
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• pp.135-147
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• 2004

This study was conducted to investigate the technical factors of Lu Yu Fu vault actually performed by three men gymnasts participated in artistic gymnastics competition of 2003 summer Universiade in Daegu through the DLT method of three dimensional cinematography. To analyze these vaults, the instant events of Lu Yu Fu were set in the board touchdown(BTD), the board takeoff(BTO), the horse touchdown(HTD), the horse takeoff(HTO), the peak height(PH), the mat touchdown(MTD) respectively and the phases of that vault were set in the board contact(BC), the preflight(PRF), the horse contact(HC), the postflight(POF), the grounding on mat(GM) respectively After calculating the performance times, the CG displacement velocity, the kinetic energy impulse reaction force moment arm torque at the horse, the released angle piked angle addressed angle, the angular momentum angular velocity of whole body in x axis, and the horizontal displacement between the feet and CG, the following conclusions were reached. To perform the better Lu Yu Fu vault, a gymnast must have the large horizontal velocity of whole body with fast run-up, decrease the duration time and the horizontal vertical displacement of whole body in PRF, have the enough time to judge the correct magnitude and direction of force to brake or push the horse so as to lengthen the HC duration time at any cost. Also it is desirable to increase the horizontal vertical displacement of whole body in POF if possible, maintain the adequate piked position to decrease the angular velocity of whole body in x axis, prepare the grounding on mat previously and delay the release of the hand from the body to keep the angular momentum.

• Korean Journal of Applied Biomechanics
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• v.27 no.3
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• pp.219-227
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• 2017

Objective: The aim of this study was to analyze the effects of bobsleigh shoes on the lower extremity range of motion and start speed lap time and to develop bobsleigh shoes suitable for winter environments and Korean players based on sports science and optimized biomechanical performance. Background: The bobsleigh shoes used in the start section of the sport are one of the most important equipment for improving athletes' performances. Despite the importance of the start section, there are no shoes that are specifically designed for Korean bobsleigh athletes. Thus, Korean athletes have to wear sprint spike shoes instead of bobsleigh shoes to practice the start. Method: The subjects included four bobsleigh athletes from the Gangwon Province Bobsleigh Skeleton Federation. The study selected the bobsleigh shoe type A (company A) and type B (company B). We analyzed the lower extremity range of motion and sprint time (start line to 10 m) using a Motion Analysis System (USA). Results: In the measurement of the time required for the bobsleigh start section (10 m), the type A shoes demonstrated the fastest section record by $2.765{\pm}0.086sec$ and yielded more efficient movements, hip and knee flexion, hip extension, ankle dorsiflexion, plantar flexion, and inversion than the type B shoes. Conclusion: Type A shoes can yield a better performance via effective lower extremity movements in the bobsleigh start section. Application: In the future, functional analysis should be conducted by comparing the upper material properties, comfort, and muscle fatigue of bobsleigh shoes based on the Type A shoes to develop such shoes suitable for Koreans.

• The Journal of Advanced Prosthodontics
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• v.10 no.1
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• pp.73-78
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• 2018

PURPOSE. The purpose of this study was to analyze the effects of two different implant surface treatments on initial bone connection by comparing the Removal Torque Values (RTQs) at 7 and 10 days after chemically modified, sandblasted, large-grit and acid-etched (modSLA), and Laser-etched (LE) Ti implant placements. MATERIALS AND METHODS. Twenty modSLA and 20 LE implants were installed on the left and right tibias of 20 adult rabbits. RTQs were measured after 7 and 10 days in 10 rabbits each. Scanning electron microscope (SEM) photographs of the two implants were observed by using Quanta FEG 650 from the FEI company (Hillsboro, OR, USA). Analyses of surface elements and components were conducted using energy dispersive spectroscopy (EDS, Horiba, Kyoto, Japan). RESULTS. The mean RTQs were $12.29{\pm}0.830$ and $12.19{\pm}0.713$ Ncm after 7 days (P=.928) and $16.47{\pm}1.324$ and $16.17{\pm}1.165$ Ncm after 10 days (P=.867) for LE and modSLA, respectively, indicating no significant inter-group differences. Pore sizes in the LE were $40{\mu}m$ and consisted of numerous small pores, whereas pore sizes in the modSLA were $5{\mu}m$. In the EDS analysis, Ti, O, and C were the only three elements found in the LE surfaces. Na, Ca, Cl, and K were also observed in modSLA, in addition to Ti, O, and C. CONCLUSION. The implants showed no significant difference in biomechanical bond strength to bone in early-stage osseointegration. LE implant can be considered an excellent surface treatment method in addition to the modSLA implant and can be applied to the early loading of the prosthesis clinically.

• Korean Journal of Applied Biomechanics
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• v.15 no.2
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• pp.83-92
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• 2005

Computer-assisted motional analysis is a popular method in biomechanical studies. Validation of the specific system and its measurement are fundamental to its application in the areas. Because the accuracy and consistency of a particular system provide the researchers with critical information to assist in making judgements regarding the degree to which inferences can be drawn from measurement data. The purpose of this study was to assess the accuracy and consistency of the Kwon3D motion analysis system. Validation parameters were five lengths from eight landmarkers in combination with the DLT reconstruction error values, digitizing monitor resolutions, and numbers of control points. With the best setting, Kwon3D's estimations of 260cm, 200cm, 140cm, 100cm, and 20cm were $260.33{\pm}.688cm$, $199.98{\pm}.625cm$, $139.89{\pm}.537cm$, $99.75{\pm}.466cm$, $20.08{\pm}.114$, respectively. There was no significant DLT error value difference between two monitor resolutions, but 0.27cm significant difference in 260cm estimation. There were significant differences in 260cm and 200cm estimations between with 33-control-point DLT error and with 17-control-point DLT error, but no in 140cm, 100cm, and 20cm estimations. Test-retest results showed that Kwon3D measurements were highly consistent with reliability coefficients alpha of .9263 and above.

• Journal of Korean Neurosurgical Society
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• v.53 no.4
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• pp.223-227
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• 2013

Objective : Although there is no consensus on the ideal treatment of the craniocervical instability, biomechanical stabilization and bone fusion can be induced through occipito-cervical fusion (OCF). The authors conducted this study to evaluate efficacy of OCF, as well as to explore methods in reducing complications. Methods : A total of 16 cases with craniocervical instability underwent OCF since the year 2002. The mean age of the patients was 51.5 years with a mean follow-up period of 34.9 months. The subjects were compared using lateral X-ray taken before the operation, after the operation, and during last follow-up. The Nurick score was used to assess neurological function pre and postoperatively. Results : All patients showed improvements in myelopathic symptoms after the operation. The mean preoperative Nurick score was 3.1. At the end of follow-up after surgery, the mean Nurick score was 2.0. After surgery, most patients' posterior occipito-cervical angle entered the normal range as the pre operation angle decresed from 121 to 114 degree. There were three cases with complications, such as, vertebral artery injury, occipital screw failure and wound infection. In two cases with cerebral palsy, occipital screw failures occurred. But, reoperation was performed in one case. Conclusion : OCF is an effective method in treating craniocervical instability. However, the complication rate can be quite high when performing OCF in patients with cerebral palsy, rheumatoid arthritis. Much precaution should be taken when performing this procedure on high risk patients.

• Journal of the Korean Society of Safety
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• v.12 no.3
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• pp.178-184
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• 1997

Many mathematical techniques have been developed to determine the muscle forces and force distribution in biomechanical human model, because it is so important to understand internal forces resisting external loading. However, a three-dimensional mathematical model of wrist joint, which is essential to develop solid modeling and artificial wrist joint, has not been well developed. This study proposed to define three-dimensional mathematical model of distal radius and ulna of the human wrist and to develop a detailed two-dimensional finite element through comparisons to existing analytical models and experimental tests. This mathematical model were accurately recreated, allowing the internal tendon force as well as force transmission and distribution through the distal radios and ulna during dynamic loadings. The results found in this study indicate and support the findings of other investigator that cyclic loading condition results in higher compression force on distal radius and ulna and may be source of wrist disorder.

• Journal of Biomedical Engineering Research
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• v.34 no.3
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• pp.111-116
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• 2013

Finite element analysis(FEA) has been extensively applied in the analyses of biomechanical properties of stents. Geometrically, a closed-cell stent is an assembly of a number of repeated unit cells and exhibits periodicity in both longitudinal and circumferential directions. This study concentrates on various parameters of the FEA models for the analysis of drug-eluting biodegradable polymeric stents for application to the treatment of coronary artery disease. In order to determine the mechanical characteristics of biodegradable polymeric stents, FEA was used to model two different types of stents: tubular stents(TS) and helicoidal stents(HS). For this modeling, epigallocatechin-3-O-gallate (EGCG)-eluting poly[(L-lactide-co-${\varepsilon}$-caprolactone), PLCL] (E-PLCL) was chosen as drug-eluting stent materials. E-PLCL was prepared by blending PLCL with 5% EGCG as previously described. In addition, the effects of EGCG blending on the mechanical properties of PLCL were investigated for both types of stent models. EGCG did not affect tensile strength at break, but significantly increased elastic modulus of PLCL. It is suggested that FEA is a cost-effective method to improve the design of drug-eluting biodegradable polymeric stents.