• The Journal of Advanced Prosthodontics
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• v.8 no.2
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• pp.131-136
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• 2016

PURPOSE. The aim of this study was to observe stress concentration in the implant, the surrounding bone, and other components under the pull-out force during the crown removal. MATERIALS AND METHODS. Two 3-dimensional models of implant-supported conventional metal ceramic crowns were digitally constructed. One model was designed as a vertically placed implant ($3.7mm{\times}10mm$) with a straight abutment, and the other model was designed as a 30-degree inclined implant ($3.7mm{\times}10mm$) with an angled abutment. A pull-out force of 40 N was applied to the crown. The stress values were calculated within the dental implant, the abutment, the abutment screw, and the surrounding bone. RESULTS. The highest stress concentration was observed at the coronal portion of the straight implant (9.29 MPa). The stress concentrations at the cortical bone were lower than at the implants, and maximum stress concentration in bone structure was 1.73 MPa. At the abutment screws, the stress concentration levels were similiar (3.09 MPa and 3.44 MPa), but the localizations were different. The stress at the angled abutment was higher than the stress at the straight abutment. CONCLUSION. The pull-out force, applied during a crown removal, did not show an evident effect in bone structure. The higher stress concentrations were mostly observed at the implant and the abutment collar. In addition, the abutment screw, which is the weakest part of an implant system, also showed stress concentrations. Implant angulation affected the stress concentration levels and localizations. CLINICAL IMPLICATIONS. These results will help clinicians understand the mechanical behavior of cement-retained implant-supported crowns during crown retrieval.

• Journal of Soil and Groundwater Environment
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• v.17 no.1
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• pp.8-12
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• 2012

This study is maintains the condition of high temperature (above $600^{\circ}C$) within a short time using on microwave and high temperature heating elements. And removal characteristics according to changes in soil moisture, microwave power and temperature through the decomposition of the contaminated soil by oil. The difficulty resolvability material was sort of lubricating oil having long carbocyclic (C18-C50) and TPH removal rate reached 85.2% at 6 kW and $700^{\circ}C$ and thus the contaminant was removed 1,788 mg/kg within a process time of 40 minutes. In the case of light oil, gasoline contaminated soil, the removal amount showed 567 mg/kg and the treatment rate reached 98.4% at 6 kW, $500^{\circ}C$ and 20 minute. In the case of non-resolvability reached TPH concentrations on 2,000 mg/kg of worrisome level of soil contamination in the 3 zones at 6 kW, $700^{\circ}C$ and 30 minute. At the time, showed up processing costs 8,173 won per ton.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.2
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• pp.209-216
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• 2008

Statement of problem: It is difficult about assessing the loosening tendency of conical connection type implant after cyclic loading with diamond like carbon coating one-piece abutments, and also about the retightening effect. Purpose: This study was performed to investigate the influence of one-piece abutment screw retightening after $5.0{\times}10^{4}$ cyclic loading and Diamond like coating Material and methods: Thirty two ITI implant were divided to 4 groups. Group 1,3-titanium abutment, group 2,4 - diamond like carbon coated abutment. Group 1,2 - $20.0{\times}10^{4}$ cyclic loading after $5.0{\times}10^{4}$ cyclic loading, Group 3,4- after $20.0{\times}10^{4}$ Cyclic loading. After cyclic loading, periotest values were taken and removal torque values of abutments were measured with a digital torque gauge. Results: 1. The removal torque of group 2 after $5.0{\times}10^{4}$ cyclic loading is slightly greater than the other groups but not significantly higher than others (P>0.05). 2. The final removal torque values after $20.0{\times}10^{4}$ cyclic loading of group 1 is bigger than group 3, and group 2 is bigger than group 4, but not significantly higher (P>0.05). 3. The final removal torque values after $20.0{\times}10^{4}$ cyclic loading of all groups are not significantly different (P>0.05).

• Journal of Applied Reliability
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• v.12 no.1
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• pp.35-46
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• 2012

Wood pellet is one of biomass energy fuels, which is produced by compressing woody biomass such as sawdust, planer shavings, and whole-tree removal or tree tops and branches leftover after logging into cylindrical form. Latterly much attention has been paid to wood pellet boiler which is suitable for use at various scales in domestic and industrial furnaces for heat production to replace conventional fossil fuel energy sources since the use of wood pellet that is carbon neutral can alleviate global warming. This study presents the result of developing a high efficiency wood pellet boiler with 55MJ/h capacity. Efficiency has been improved by using a rotating disk burner with a shorter screw feeder. Special attention has been paid to the improvement of the safety of the wood pellet boiler from backfire by adopting a double protecting system composed of a shutter and an air curtain. The result shows that the efficiencies of the wood pellet boiler are 97.2% and 89.2% based on lower and higher heating values, respectively, at 15.1kW of heating output.

• Journal of Korean Foot and Ankle Society
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• v.13 no.1
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• pp.80-84
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• 2009

Purpose: The purpose of this article is to assess the efficacy of a bioabsorbable polylactide (PLA) plate and screw for treating injuries of ankle fractures. Materials and Methods: 24 patients who underwent an open reduction and internal fixation operation for ankle fractures from July 2005 to March 2007 were enrolled into the study. There were 15 men and 9 women. The average age of the patients was 44 years and the average follow-up period was 16 years and two months (16.2 months). All cases were divided into low grade fracture patient (11) who belongs in type A and B of Danis-Weber classification and high grade fracture patient (13) who belongs in type C1, C2 of Danis-Weber classification, and each groups were analyzed by clinical (Meyer score) and radiological finding at the time of their last follow-up evaluation. Results: The clinical results according to Meyer scoring system, showed that all patient with low grade fracture had good to excellent result, but only 54% of patient with high grade fracture had good to excellent result. According to Cedell's radiologic finding, there were 91% cases above fair in low grade fracture. But there were 62% of patient above fair result in high grade fracture, the reduction losses were seen in 38% of patient with high grade fracture. Conclusion: Bioabsorbable PLA plate and screw is good internal fixation device which doesn't have additional operation for removal of implant because of slow absorption within the human body. It showed sufficient strength for acquisition and maintenance of reduction in low grade fracture, but need attention to use because of many cases of reduction loss in high grade fracture. So, it seems to be safe and effective when used in heeling of low grade fracture under considering about type of fracture sufficiently.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.6
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• pp.309-316
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• 2016

In this study, sewage was fed with up flow direction into a reactor equipped with a screw to circulate media that had lower specific gravity than water. It was observed that the media in the reactor could be circulated by a screw with reverse flow of the sewage feeding from the top to the bottom direction. Under these conditions, concentrations of inflow and outflow pollutants were measured at the filtration unit. Experimental results revealed stable circulation of the media with a screw in the reactor. Circulation of the media in the reactor showed more efficiency in removing the pollutants (particulate matters and organics) than no circulation. The maximum removal efficiencies of suspended solid (SS), chemical oxygen demand (CODmn), and total phosphorus (T-P) were 96%, 72% and 65%, respectively. Improvements for SS, CODmn and T-P removals with circulation of media were 52.38%, 43.14% and 118.12% respectively, compared to those without circulation.

• 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 Korean Foot and Ankle Society
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• v.16 no.1
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• pp.38-46
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• 2012

Purpose: This study was performed retrospectively to evaluate clinical outcomes of distal metatarsal osteotomy using bio-compression screw as the joint preservation method for advanced hallux rigidus. Materials and Methods: Eleven cases were followed up for more than 1 year after distal metatarsal dorsal wedge osteotomy for advanced hallux rigidus. The clinical evaluation was performed according to the American Orthopaedic Foot and Ankle Society (AOFAS) score and patient's satisfaction score. The range of motion, and the period to return to running exercise, tip-toeing gait, squatting, walking down the stairs were evaluated. As the radiographic evaluation, the interval of $1^{st}$ MTP (metatarsophalangeal) joint space and the period to union were measured. Results: The AOFAS hallux score had improved significantly from preoperative average 50.7 points to 87.6 points at the last follow-up (p=0.005). The subjective satisfaction score was average 90.6 points. There were no case of subsequent fusion or additional operation, and no complication associated with bio-compression screw. The period to return to running exercise, tip-toeing gait, squatting, walking down the stairs were average of 24.8 weeks, 20.4 weeks, 16.8 weeks, 18.5 weeks respectively. Dorsiflexion of $1^{st}$ MTP joint had improved significantly from preoperative average $17.5^{\circ}$ to $44^{\circ}$ (p<0.001). All cases achieved union of osteotomy site, and the period to union was average 10.4 weeks. The interval of $1^{st}$ MTP joint space had improved significantly from preoperative average 1.2 mm to 3.5 mm (p=0.014). Conclusion: Distal metatarsal osteotomy using bio-compression screw seems to be one of effective treatment methods for advanced hallux rigidus, because of restoration of the first MTP joint motion, and reliable pain relief, and needlessness of hardware removal.

• Journal of the korean academy of Pediatric Dentistry
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• v.38 no.3
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• pp.250-259
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• 2011

The aim of this study was to suggest a design for an orthodontic miniscrew which may work most favorably in the thin cortical bone of the adolescent. In this study, orthodontic miniscrews with different diameters, lengths, and body types were manufactured and implanted in two artificial bone samples with different cortical bone thickness. Maximum insertion torque, maximum removal torque, and lateral alteration torque were measured. As a result, the bone quality, body type, diameter, and the length all had their effects on the maximum insertion torque, maximum removal torque, and lateral alteration torque. Cortical bone thickness was the most important factor. In initial stability, conical types showed better results than cylindrical types. Increase in the diameter had favorable effects in achieving mechanical stability. Increase in the length did not have as much influence as the other factors did on the initial stability, but there was a statistically significant difference between screws of 6 mm and 8 mm lengths(p<0.05). In conclusion, the conical type screw with a diameter of 1.8 mm is most favorable in the thin cortical bone of the adolescent. In terms of length, the 8 mm screw is expected to perform better than the 6 mm screw.

• The korean journal of orthodontics
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• v.38 no.5
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• pp.328-336
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• 2008

Objective: The purpose of this study was to compare the torque resistance to removal of sandblasted large grit and acid etched (SLA) surface treated orthodontic mini-implants and smooth surface orthodontic mini-implants as well as performing histologic observations. Methods: Two groups of custom screw shaped orthodontic mini-implants (C-implant, 1.8 mm outer diameter $\times$ 9.5 mm length, Cimplant, Seoul, Korea) were designated. 22 SLA treated C-implants (SLA group) and 22 machined surface C-implants (machined group) were placed in the tibia metaphysis of 11 adult New Zealand white rabbits. Following a 6-week healing period, the rabbits were sacrificed. Subsequently, the C-implants were removed under reverse torque rotation with a digital torque measuring device and independent t-test was performed. Selected tissues were prepared for histologic observation. Results: The SLA group presented a higher mean removal torque value (6.286 Ncm) than the machined group (4.491 Ncm) which was statistically significant (p < 0.005). Histologic observation revealed a trend of more new bone formation in contact with the screw surface in the SLA group than the smooth group. Conclusions: The results of this study suggested that SLA surface treatment can enhance the osseintegration potential for C-orthodontic mini-implants.