• The Journal of Korean Academy of Prosthodontics
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• v.48 no.1
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• pp.61-68
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• 2010

Purpose: This article attempted to determine the factors affecting the preload and screw loosening. Methods: Available clinical studies from 1981 to 2008 from the PUBMED that presented screw loosening data and review articles regarding screw joint stability were evaluated. Eleven studies dealing the biomechanical principles of the screw mechanics were reviewed. Moreover, the results of our data were included. Results: The frequency of screw loosening was consequently reduced due to the advancement in torque tightening with torque wrench, screw material, coating technique for reducing the frictional force, and thread design, etc. If preload in the screw falls below a critical level, joint stability may be compromised, and the screw joint may fail clinically. The types of fatigue failure of screw were divided to adhesive wear, plastic deformation, and screw fracture. Conclusion: An optimum preload is essential to the success of the implant-abutment complex. To maintain optimum preload, using a torque wrench and re-tightening at recall time were needed.

• The Journal of the Convergence on Culture Technology
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• v.5 no.4
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• pp.387-394
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• 2019

In this study, in order to evaluate the damage and deterioration of the track components of sleeper floating track (STEDEF), the field samples(specimens) were taken from the serviced line over 20 years old, and the track components were visually inspected, and investigated by laboratory tests and finite element analysis. As a result of visual inspection, the damage of the rail pad and fastener was slight, but the rubber boot was worn and torn at the edges of bottom. The resilience pads were clearly examined for thickness reduction and fatigue hardening layer. As a result of spring stiffness test of rail pad and resilience pad, the deterioration of rail pad was insignificant, but the deterioration of resilience pad exceeded design standard value. Therefore resilience pad was directly affected by train passing tonnage. As a result of comparing the deterioration state of the field sample and the numerical analysis result, the stress and displacement concentration position of the finite element model and the damage position of the field sample were coincident.

• Journal of dental hygiene science
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• v.2 no.1
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• pp.39-45
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• 2002

Our study shows the following results of the patterns and reality of oral health of 862 Government employees and private school employees who had received oral examinations from April to May, 2000. For the exposition of each group to dental service, the male groups(37.4%) were more exposed than the female ones(30.0%, p<0.05), while the scaling experience results indicated that more ages mean more scaling(the over 50 year group 27.1%, 41-50 group 23.9%, 31-40 group 20.5%, 21-30 group 10.8%, p<0.001). The data involving sweet food and refreshments revealed that 'positive respondents' in the male groups were 19.7% with 12.5% positive in the female ones, and 'negative respondents' were 32.3% and 51.0% in the male and female groups respectively(p<0.001). For the oral odor, the male groups(37.9%) are more severe than the female ones(25.5%, p<0.01). The results of dental caries revealed that 19.1% of the male and 13.9% of the female said 'yes'(p<0.05), with 25.1% of the male and 11.1% of the female suffering from missing teeth(p<0.001); 77.4% of the male and 51.0% of the female from periodontal disease (p<0.001).