Biomedical subjects

Byeong Hoon Cho

Publications and source records attributed to Byeong Hoon Cho.

4 recordsLinked to original sources

PubMed2006

Rheological characterization of composites using a vertical oscillation rheometer.

OBJECTIVES: The purpose of this study was to investigate the viscoelastic properties related to the handling characteristics of composites. METHODS: A custom-designed vertical oscillation rheometer (VOR) was used for the rheological measurements of composites. The VOR consists of three parts: (1) a measuring unit, (2) a deformation induction unit, and (3) a force-detecting unit. Two medium-viscous composites, Z100 and Z250, and two packable composites, P60 and SureFil, were tested. A dynamic oscillatory test was used to evaluate the storage modulus (E'), loss modulus (E''), and loss tangent (tan delta) of the composites as a function of frequency (omega) from 0.1 to 20Hz at 23 degrees C. RESULTS: The E' and E'' increased with increasing frequency and showed differences in magnitude among brands. The complex moduli E* of the composites at omega=2 Hz, normalized to that of Z100, were 2.16 (Z250), 4.80 (P60), and 25.21 (SureFil). The magnitudes and frequency characteristic of loss tangent differed significantly among brands. The relationship among the complex modulus E*, the phase angle delta, and the frequency omega was represented by the frequency domain phasor form E*(omega)e(idelta)=E*(omega) angledelta. SIGNIFICANCE: The viscoelasticities of composites, which influence handling characteristics, are significantly different among brands. The VOR is a relatively simple device for the dynamic rheological measurement of dental composites. The loci of the frequency domain phasor plots in a complex plane are a valuable method of representing the viscoelastic properties of composites.

Composite Resins↗

PubMed2005

Highly polymorphic human CYP4A11 gene.

The cytochrome P450 (CYP) is a monooxidase, which regulates metabolism of drugs and fatty acids in the liver and kidney. Among isoforms of the CYP4A subfamily, CYP4A11 is a major lauric acid (medium-length fatty acids) omega hydroxylase and is involved in the balance of lipids in the human liver. We performed direct DNA sequencing in 24 unrelated Korean individuals in the whole gene, including the 1-kb upstream region of CYP4A11. Seventy sequence variants were identified: six in exons, including two nonsynonymous SNPs; 60 in introns; and four in 3'UTR. In comparison with SNPs enrolled in the SNP database (dbSNP) of the National Center for Biotechnology Information (NCBI), 26 novel polymorphisms (24 in introns and two in 3'UTR) were identified in Korean subjects (n=24). The distributions of polymorphisms confirmed were significantly different from those in the dbSNP of the NCBI. Information clarified in this study would provide valuable for further studies, including genetic association studies for various diseases and drug responses.

3' Untranslated Regions↗

PubMed2005

Interpretation of bond failure through conversion and residual solvent measurements and Weibull analyses of flexural and microtensile bond strengths of bonding agents.

OBJECTIVES: An inverse correlation between initial acetone content of bonding agents and microtensile bond strength (MTBS) has previously been reported. Here it was investigated whether the inferior MTBS of acetone-rich bonding agents was caused by flaws and low adhesive layer strength, insufficient to resist polymerization shrinkage stresses of the overlying composite. METHODS: Bonding solutions with (27-67) mass fraction% acetone were dried for 10 s or 30 min. Specimens for infrared (IR) spectroscopy and flexural strength (FS) were cured for 10 s (cure mode 1) to represent the adhesive layer properties when polymerizing the composite resin or for 10 s plus an additional 60 s through composite resin (cure mode 2) to represent adhesive layer properties when testing the bond strength. Degree of conversion (DC) and residual acetone content were evaluated for films by mid-IR and bulk specimens by near-IR spectroscopy. FS and MTBS data using these bonding solutions were interpreted by Weibull statistics and ANOVA (alpha = 0.05). RESULTS: In bulk specimens, initial and residual acetone content were positively correlated (P = 0.003). FS in cure mode 1 was significantly lower than in cure mode 2 and decreased with increasing initial acetone content, while DC remained consistent, suggesting pores from acetone evaporation as flaw initiating sites affecting the mechanical adhesive properties. SIGNIFICANCE: From DC and Weibull analyses of MTBS and FS, early low strength of the adhesive layer and shrinkage stresses acting on pre-existing flaws are suggested as critical factors affecting the dentin/adhesive bond strength.

Acetone↗

PubMed2004

Aminoacyl-tRNA synthetase complexes: beyond translation.

Although aminoacyl-tRNA synthetases (ARSs) are housekeeping enzymes essential for protein synthesis, they can play non-catalytic roles in diverse biological processes. Some ARSs are capable of forming complexes with each other and additional proteins. This characteristic is most pronounced in mammals, which produce a macromolecular complex comprising nine different ARSs and three additional factors: p43, p38 and p18. We have been aware of the existence of this complex for a long time, but its structure and function have not been well understood. The only apparent distinction between the complex-forming ARSs and those that do not form complexes is their ability to interact with the three non-enzymatic factors. These factors are required not only for the catalytic activity and stability of the associated ARSs, such as isoleucyl-, methionyl-, and arginyl-tRNA synthetase, but also for diverse signal transduction pathways. They may thus have joined the ARS community to coordinate protein synthesis with other biological processes.

Amino Acyl-tRNA Synthetases↗