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- 저자 : Escobar-Correa, Natalia (검색결과 3 건)
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Escobar-Correa, Natalia,Ramirez-Bustamante, Maria Antonia,Sanchez-Uribe, Luis Alejandro,Upegui-Zea, Juan Carlos,Vergara-Villarreal, Patricia,Ramirez-Ossa, Diana Milena The Korean Association Of Orthodontists 2021 대한치과교정학회지 Vol.51 No.1
Objective: To evaluate the mandibular buccal shelf (MBS) in terms of the angulation and bone depth and thickness according to sex, age, and sagittal and vertical skeletal patterns in a Colombian population using cone-beam computed tomography (CBCT). Accordingly, the optimal site for miniscrew insertion in this area was determined. Methods: This descriptive, retrospective study included 64 hemi-arches of 34 patients. On CBCT images, the angulation, buccal bone depth (4 and 6 mm from the cementoenamel junction [CEJ] of MBS), and buccal bone thickness (6 and 11 mm from the CEJ of MBS) were measured at the mesial and distal roots of the mandibular first and second molars. Results: There were no statistically significant differences in the angulation, depth, and thickness of MBS between male and female patients. The values for the bone around the distal root of the mandibular second molar were significantly greater than the other values. The osseous characteristics were significantly better in participants aged 16-24 years. Class III patients exhibited the best osseous characteristics, with the bone depth at 6 mm being significantly different from that in Class I and Class II patients. Although values tended to be greater in patients with low angles, the difference was not statistically significant. Conclusions: MBS provides an optimal bone surface for miniscrew insertion, with better osseous characteristics at the distal root of the mandibular second molar, 4 mm from CEJ. Adolescent patients, Class III patients, and patients with a low angle exhibit the most favorable osseous characteristics in the MBS area.
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Improved Mg–Al–Zn Magnesium Alloys Produced by High Energy Milling and Hot Sintering
Y. Galindez,E. Correa,A. A. Zuleta,A. Valencia‑Escobar,D. Calderon,L. Toro,P. Chacón,F. Echeverría E. 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5
Powders of commercially pure magnesium (c.p. Mg), AZ91 magnesium alloy and zinc were milled using a high-energy mill.The effect of high energy milling (HEM) on powders morphology, chemical composition, crystallite size and compactionof different powders mixtures were studied. After compaction, samples were thermally treated at 450 °C and both densityand hardness were evaluated. It was found that as milling speed and time increases, the AZ91 alloy and c.p. Mg particleswere deformed and fractured up to sizes below 10 μm. X-ray diffraction patterns for both the c.p. Mg and the AZ91 powdersrevealed that the milling process induced changes in both the α-Mg and the β-Mg17Al12 phases. By increasing the millingspeed, the crystallite size decreases by up to 70% for AZ91 powders and by 80% for magnesium powders. The relativedensities of the compacted AZ samples were greater than 85% and this parameter increased for all samples after thermaltreatment at 450 °C, obtaining densities higher than 88%. Hardness measurements disclosed values as high as 84.3 HR15T.Theoretical calculations of mechanical strength were obtained for all samples based on the hardness values measured, findingvery encouraging results for the three Mg alloys.
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Intermetallic-Rich Layer Formation for Improving Corrosion Resistance of Magnesium Alloys
D. Calderón,Y. Galindez,L. Toro,A. A. Zuleta,A. Valencia‑Escobar,P. Chacón,E. Correa,F. Echeverría 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.3
The present work examines the formation of a corrosion protective coating containing intermetallic phases on magnesiumalloy substrates. The protective coating was formed on the surfaces of commercially pure magnesium (cp Mg) and AZ31Bmagnesium alloy by vacuum thermal evaporation of commercially pure aluminium (cp Al) and a subsequent heat treatmentof the sample. This coating was continuous, homogenous and its microstructure was a eutectic phase composed by clustersof α-Mg surrounded by β phase (Mg17Al12). This eutectic-type coating provided 168 and 504 h of protection inside the saltspray chamber for the cp Mg and AZ31 alloy samples, respectively. To achieve this, it was required to deposit at least 5.5 μmof cp Al and then perform a combined thermal treatment involving heating the samples to 583 K for 60 min and then raisingthe temperature to 693 K for 5 min.
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