Yeong-Mu Ko

Antimicrobial effect of Korean propolis against the mutans streptococci isolated from Korean

The aim of this study was to determine the optimal concentration of Korean propolis against clinical isolates of mutans streptococci (MS) from Koreans. The antimicrobial activity was evaluated using the minimum inhibitory concentration (MIC) and time-kill curves against mutans streptococci. The MIC90 values of propolis for MS were 35 μg/ml. Propolis had a bacteriostatic effect on Streptococcus mutans ATCC 25175T and bactericidal effects on Streptococcus sobrinus ATCC 33478T at > 2×MIC (70 μg/ml). These results suggest that the propolis can be used in the development of oral hygiene products for the prevention of dental caries.

Effect of Functional Groups on Biodegradation and Pre-osteoblastic Cell Response on the Plasma-Polymerized Magnesium Surface

Magnesium (Mg) is light, has biocompatibility, and has mechanical properties close to those of natural bone. However, pure Mg severely corrodes in a physiological environment, which may result in fracture prior to substantial tissue healing. In this study, the Mg surface was modified by depositing a thin polymeric film containing COOH, NH2, and OH groups through plasma polymerization of acrylic acid, allyl amine, and allyl alcohol in order to improve its anticorrosion and bioactive properties. The –COOH group had a significant effect on bonelike apatite formation compared with –NH2 and –OH. It was also concluded that a bonelike-apatite formed COOH/Mg surface was more effective for reducing biodegradation rate than the other surfaces. The results of in vitro cell test revealed significantly enhanced cell proliferation and differentiation on the COOH/Mg and NH2/Mg surfaces compared with other surfaces.

Interface activation and surface characteristics of Ti/TiN/HA coated sintered stainless steels

Interface activation and surface characteristics of Ti/TiN/HA film coated sintered stainless steels (SSS) have been investigated by electrochemical and biocompatibility tests. HA (hydroxyapatite), Ti, and Ti/TiN film coatings were applied using electron-beam deposition method (EB-PVD). Ti, Ti/TiN, and Ti/TiN/HA film coated surfaces and layers were investigated by SEM and XPS. The coated films showed micro-columnar structure, and Ti/TiN/HA films were denser than Ti or HA-only film. The corrosion resistance of the HA coating was similar to that of Ti/TiN/HA film coating when Cu content reached 4 wt.%, but the corrosion resistance of the HA coating decreased when Cu content increased from 4 wt.% in 0.9% NaCl solution. Therefore, HA-only coating could ensure corrosion resistance when Cu content does not exceed 4 wt.%. The results of biocompatibility tests of SSS on dogs showed that bone formation and biocompatibility were favorable when Cu content did not exceed 4 wt.%. The biocompatibility with bone was generally favorable in Ti/TiN/HA film coating and HA-only coating, while bone formation was somewhat faster for the HA film coated surface than for the Ti/TiN/HA film coating. Also, good cell growth and osseointegration without toxicity were observed.

Electrochemical behavior of TiN film coated Ti−Nb alloys for dental materials

In order to study the electrochemical behaviors of TiN film coated Ti−Nb alloys for dental materials, Ti containing Nb up to 3, 20, and 40 wt.% was melted by a vacuum furnace and coated with TiN by EB-PVD. the electrochemical behaviors were investigated using a potentiostat in 0.9% NaCl solution and the corrosion surface was observed using SEM and XPS. Ti−3Nb and Ti−20Nb alloys have α+β phase structure. In the case of Ti−40Nb, the microstructure had a coarse β phase. The microstructural changed from equiaxed to acicular and an increase of β-phase in Ti−Nb alloys was observed with increased Nb content. The current density at 300 mV (potential of oral environment) of Ti−40Nb alloy was lower than that of the other alloys in 0.9% NaCl. The pitting corrosion resistance of Ti−40Nb was higher than that of Ti−3Nb and Ti−20Nb alloys in the 0.9% NaCl solution. The corrosion potential and pitting potential of TiN coated Ti alloy increased with increasing Nb content but the current density at 300 mV and the current density at the passive region decreased. The TiN coated Ti−40Nb alloy offers good corrosion resistance for dental implants compared with non-TiN coats alloys.

Evaluation of degradation in nanofilled adhesive resins using quantitative light-induced fluorescence

The aim of this study was to evaluate degradation in commercial dental nanofilled adhesive resins using quantitative light-induced fluorescence (QLF). Three adhesives were selected: D/E resin (DR), Single Bond Plus (SB), and G-Bond (GB). The adhesives were mixed with porphyrin for the QLF analysis. Specimens were prepared by dispensing blended adhesives into a flexible mold and polymerizing. Then, the QLF analysis of the specimens was done and the porphyrin values (Simple Plaque Score and ΔR) were measured. After thermocycling of the specimens (5000 cycles, 5 to 55°C) for the degradation, the specimens were assayed by QLF again. The porphyr in values were analyzed using paired t-test at a 95% confidence level. A significant reduction in SPS was observed in all groups after thermocycling. The ΔR significantly decreased after thermocycling except area ΔR30 of SB group. Overall, porphyrin values decreased after thermocycling which indicates that the degradation of the adhesive resins may be measured by the change of porphyrin value. The QLF method could be used to evaluate the degradation of adhesive resin.

Biocompatibility of Cation Coated on Plasma-Polymerized Ti Surface

In this study, we investigated the bone formation properties and cell responses on Na-, Mg-, K-, and Ca-ion-exchanged carboxyl plasma polymerized titanium (Ti) surfaces. The phase and morphologies of deposits bonelike apatite were significantly influence by the cation species. Na and Mg ions promote bonelike apatite nucleation and growth on plasma-functionalized Ti surfaces in simulated body fluid (SBF) and improves the crystallinity of the bonelike apatite deposited layer. The cell viability tests revealed significantly enhanced viability on the Ca-ion-exchanged plasma-functionalized Ti surface than on any other surface.

Electrochemical Properties of Ti-30Ta-(3~15)Nb Alloys Coated by HA/Ti Compound Layer

Electrochemical properties of Ti-30Ta-Nb alloys coated by HA/Ti compound layer have been studied by various electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10, and 15 wt% Nb contents were manufactured by the vacuum furnace system. The specimens were homogenized for 24 hrs at . The samples were cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The HA/Ti non-coated and coated morphology of Ti alloy were analyzed by x-ray diffractometer(XRD) and filed emission scanning electron microscope(FE-SEM). The corrosion behaviors were investigated using potentiodynamic method in 0.9% NaCl solution at . The homoginazed Ti-30Ta-)Nb alloys showed the phase, and phase peak was predominantly appeared with increasing Nb content. The microstructure of Ti alloy was transformed from needle-like structure to equiaxed structure as Nb content increased. HA/Ti composite surface showed uniform coating layer with 750 nm thickness. The corrosion resistance of HA/Ti composite coated Ti-alloys were higher than those of the non-coated samples in 0.9% NaCl solution at . Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.

Thymosin β4 Reduces H2O2 Induced Oxidative Stress in MC3T3-E1 Cells on Titanium Surface

Thymosin β4 (Tβ4) is known to inhibit an inflammatory response and to increase the survival of osteoblasts on titanium (Ti) surfaces. Ti is the most widely used graft material in dentistry; however, an inflammatory response induced following implant placement results in the generation of reactive oxygen species (ROS). The oxidative stress from the production of ROS such as nitric oxide (NO) and hydrogen peroxide (H2O2) can damage surrounding cells, resulting in implant failure by decreasing cell viability. Thus, the aim of this study was to determine the biological effects of Tβ4 on the oxidative stress induced to MC3T3-E1 preosteoblasts on the Ti surface. Based on an MTT assay and bromodeoxyuridine immunofluorescence staining, Tβ4 was found to increase the proliferation of the H2O2-exposed MC3T3-E1 cells on Ti discs. Reverse transcription-polymerase chain reaction and western blot analyses showed that Tβ4 decreased the mRNA and protein expression levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in H2O2-exposed MC3T3-E1 cells on the Ti discs. Tβ4 inhibited the synthesis of intracellular ROS and the secretion of NO and prostaglandin E2 (PGE2) from H2O2-exposed MC3T3-E1 cells on the Ti discs. In conclusion, Tβ4 inhibits H2O2-induced iNOS and COX-2 expression with a decrease in ROS, NO, and PGE2 synthesis, which leads to improved cell survival with low cytotoxicity under an oxidative stress condition in MC3T3-E1 cells on the Ti surface. This suggests that Tβ4 may be a crucial molecule to reduce oxidative stress-induced cell damage or hypoxia, leading to promoted osseointegration on the Ti surface during implant placement.

Electrochemical Deposition of Hydroxyapatite Substituted with Magnesium and Strontium on Ti–6Al–4V Alloy

In the present study, electrochemical deposition of hydroxyapatite substituted with magnesium and strontium on Ti-6Al-4V alloy have investigated. Mg and Sr-doped HAp was coated using subsequently pulsed electrochemical deposition process at 85 °C in the solution contained Ca, Mg, Sr, and P ion. The morphology of Mg/Sr-HAp formed on implant was investigated using scanning electron microscopy and X-ray diffraction. HAp grain size and XRD intensity decreased with Mg2+ and Sr2+ ions. The initial current density was changed with addition of Mg and Sr ion concentration when the constant voltage was applied to specimens. The morphologies and phase of HAp coated layers were affected by the Mg and Sr ion concentration. Results suggest that Mg/Sr-HAp layer formed on Ti can be a potential candidate for dental materials application.