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BioOss와 Orthoblast II를 이용한 상악동 골이식술
김영균,김수관,임성철 대한치과이식임플란트학회 2006 The Korean Academy of Implant Dentistry Vol.25 No.2
We performed sinus bone graft using small amount of autogenous bone, Orthoblast?? II and BioOss?? and covered the sinus window with Ossix?? membrane in these case series. After 4.5 to 6 months after operation, histopathologic examinations of trephine core biopsy showed following results. 1. There was bone density of 43 to 87% and we could observe the favorable early new bone formation. 2. Active bony remodeling of woven and lamellar bone was observed during 4.5 to 6 months healing period.
Metal Injection Molding 공정으로 제조된 Fe-Cr-Ni계 HK30 합금의 미세조직 및 상·고온 인장 특성에 미치는 열간 등압 성형의 영향
김영균,윤태식,이기안 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.2
This study manufactured Fe-Cr-Ni-based alloy (HK30) using the metal injection molding (MIM) process and investigated the microstructure and room·high temperature mechanical properties of the material. The effect of hot isostatic pressing (HIP) on properties was also examined. The average grain sizes were 24.1 μm for an MIM specimen and 29.1 μm for an MIM+HIP specimen. Microstructure and phase analysis results confirmed that the matrix mainly consisted of γ-Fe, and Cr23C6 phase. To evaluate the mechanical properties of the material, tensile tests were performed at room temperature and 900 oC. The tensile tests at room temperature indicated that the MIM and MIMTHIP specimens showed tensile strength of 609.6 MPa and 645.0 MPa, and elongation of 32.7% and 43.7%, respectively. In both strength and elongation, the MIM+HIP sample had greater performance. The tensile results at 900 oC also showed that the HIP+MIM specimen had higher strength and elongation. This was attributed to fewer macro cracks, denser structures and finer distribution of Nb based carbide due to the additional HIP. This study also discussed the deformation behavior of MIM material at room·high temperatures.
Fe-14Cr계 페라이틱 산화물 분산 강화강의 고온 압축 및 크리프 특성에 미치는 열처리의 영향
김영균,주연아,박종관,김휘준,공만식,이기안 대한금속·재료학회 2017 대한금속·재료학회지 Vol.55 No.12
This study investigated the microstructure and the ambient-elevated temperature compression and elevated temperature creep properties of Fe-14Cr ferritic ODS steel manufactured by mechanical alloying (high energy ball milling) and hot extrusion processes. Initial microstructural observation of the as-extruded material identified elongated grains in the direction of extrusion; however, some recrystallization and grain growth were observed in the heat-treated material. The average grain sizes of the as-extruded material and heat-treated material were 0.4 and 1.1 μm, respectively. In addition, the heat treatment resulted in the increase in number density and the decrease in size of the nanocluster. A room temperature compression tests confirmed the heat-treated materials (1457 MPa) had relatively higher yield than the as-extruded material (1377 MPa), and a general tendency was observed that the difference in yield strength decreased as temperature increased. Furthermore, elevated temperature compressive creep tests confirmed that the heat-treated material had relatively greater creep resistance compared to the as-extruded material at all stress levels.
CaO 첨가 AZ31 압출재의 개량된 미세조직이 인장, 고주기 피로 및 피로 균열 전파 특성에 미치는 영향
김영균,김민종,황유진,김세광,임현규,이기안 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.6
The effect of tailored microstructures in 0.5 wt% CaO added AZ31 on tensile, high-cycle fatigue, and fatigue crack growth properties was examined. By adding CaO, the average grain size (AGS) was significantly reduced from 4.25±2.32 μm (conventional AZ31) to 2.42±1.60 μm (CaO-AZ31). The fineprecipitates of CaO-AZ31 were more evenly distributed and their fraction was higher than those of conventional AZ31. The fine-precipitates were identified as Al8Mn4Ca and (Mg, Al)2Ca in CaO-AZ31, meanwhile, were identified as Al8Mn5 and Mg17Al11 in conventional AZ31. The tensile test results showed that the yield strengths of CaO-AZ31 and conventional AZ31 were 238.0 MPa and 206.7 MPa, respectively. The elongation-to-failure also increased when CaO was added. The improved tensile properties of CaO-AZ31 could be explained by grain refinement and precipitation hardening. The high-cycle fatigue limit also increased about 15% with added CaO. The fatigue limits as a function of the tensile strengths of CaO-AZ31 and conventional AZ31 were 0.508 and 0.457, respectively. The origin of the improved fatigue resistance was attributed to inhibition of the formation of DTs, which acted as the fatigue crack source, in CaO-AZ31. In contrast, the fatigue crack growth property did not change when CaO was added. Based on the above findings, the relationships between microstructure, mechanical properties and deformation mechanisms are also discussed.
Regional Cortical Thickness in Children and Adolescents with Obesity
김영균,김세홍,김태홍,정주혜,은영미 대한가정의학회 2021 Korean Journal of Family Practice Vol.11 No.1
Background: Previous studies have demonstrated obesity-associated changes in the brain in adults; however, no study has evaluated the corticalthickness or subcortical volumes in obese children and adolescents. The purpose of our study was to investigate changes in cortical thickness inasymptomatic children and adolescents with obesity. Methods: A total of 21 participants (10 patients with obesity and 11 subjects without obesity), aged 6–18 years, underwent 3T brain magneticresonance imaging (MRI) scanning, and cortical thickness was compared between the obese group and the control group across multiple locations. The subcortical volumes were also compared on a structure-by-structure basis. Results: No significant differences between the obese and non-obese control group were observed with respect to the mean volumes of the totalwhite matter in each hemisphere. However, the obese group showed a significant reduction in the mean cortical thickness of both hemispherescompared to the control group. Group comparison analysis of the regional cortical thicknesses between the two groups also revealed a significantreduction in the cortical thickness of the left supramarginal, inferior parietal, pars orbitalis, and pars opercularis cortices in the obese groupcompared with that in the control group (P<0.05, false discovery rate corrected). Conclusion: We demonstrated a significant reduction in the thickness of the cortical areas of obese patients, especially in areas involved in body weightcontrol. Our results suggest the existence of structural brain abnormalities in obese children and adolescents, and further prospective studies arerequired to evaluate this relationship.
김영균,윤필영,엄인웅,이효정,이양진,배지현,이준호 대한치과보철학회 2014 The Journal of Advanced Prosthodontics Vol.6 No.6
This case series evaluated the clinical efficacy of autogenous tooth bone graft material (AutoBT) in alveolar ridge preservation of an extraction socket. Thirteen patients who received extraction socket graft using AutoBT followed by delayed implant placements from Nov. 2008 to Aug. 2010 were evaluated. A total of fifteen implants were placed. The primary and secondary stability of the placed implants were an average of 58 ISQ and 77.9 ISQ, respectively. The average amount of crestal bone loss around the implant was 0.05 mm during an average of 22.5 months (from 12 to 34 months) of functional loading. Newly formed tissues were evident from the 3-month specimen. Within the limitations of this case, autogenous tooth bone graft material can be a favorable bone substitute for extraction socket graft due to its good bone remodeling and osteoconductivity.