Papers by Author: Yong Keun Lee

Abstract: Bioactive poly(e-caprolactone)-siloxane hybrid material was newly developed and its in vitro and in vivo evaluations were made for the potential application as a bone substitute. The polymer precursor, triethoxysilane end capped poly(e-caprolactone) was prepared by the reaction with a,w-hydroxyl poly(e-caprolactone) and 3-isocyanatopropyl triethoxysilane with 1,4-diazabicyclo [2,2,2] octane as a catalyst and toluene as a solvent. The triethoxysilane end capped poly(e-caprolactone) was hydrolyzed and condensed to yield a hybrid sol-gel material. The gelation was carried out for 1 week at ambient condition in a covered Teflon mold with a few pinholes and then dried under vacuum at room temperature for 48 h. Its bioactivity was evaluated by examining the apatite formation on its surface in the SBF and its osteoconductivity was assessed in the tibia of white rabbit. The hybrid material showed apatite-forming ability in the SBF within 1 week soaking. Besides, new bone was formed on the surface of a cylindrical shaped specimen with no histologically demonstrable intervening non-osseous tissue after 6 weeks implantation. There was no evidence of inflammation or foreign body reaction. From the results, it can be concluded that this newly developed hybrid material has osteoconductivity and is likely to be used for the application as a bone graft substitute.

Abstract: The purpose of this study was to evaluate the cell affinity of calcium phosphate glass scaffold in the system of CaO-CaF2-P2O5-MgO-ZnO, which is already reported that promoted the bone-like tissue formation in vitro and formed new bone in Sprague-Dawley rats. We prepared calcium phosphate glass saffolds with three-dimensionally interconnected pores of 200~500 µm. Commercial HA scaffold was employed as a control in this study. Bone marrow cells were collected from the healthy human donors and cultured within the prepared scaffolds. After 2, 4, 6, and 8 weeks, hMSCs/scaffold were fixed and stained with hematoxylin and eosin. hMSCs were continuously proliferated both in the experimental and control groups at every incubation period. The number of cells was higher in the experimental group than that of the control group, however, there was no significant difference (p>0.05). Extracellular matrices could be observed at the 2nd and 4th days in the experimental and control groups, respectively. The extracellular matrices were more abundant in the experimental group at all periods. The prepared calcium phosphate glass scaffolds are expected effective in bone tissue engineering.

Abstract: The purpose of this study was to compare the bone regenerative effect of calcium phosphate glass and glass-ceramics in the system of CaO-CaF2-P2O5-MgO-ZnO, which is already reported that promoted the bone-like tissue formation in vitro and formed new bone in Sprague-Dawley rats. We prepared calcium phosphate glass and glass-ceramics with Ca/P ratio of 0.6 using the system CaO-CaF2-P2O5-MgO-ZnO and subsequently milled to 400 µm. 4×4 mm 1-wall intrabony defects of six beagle dogs were surgically created and used in this study. 8 weeks after transplantation of the prepared calcium phosphate glass and glass-ceramics in the experimental group 1 and 2, respectively, the animals were sacrificed. No root resorption or ankylosis were observed in all groups. It can be examined that the prepared glass-ceramics were more effective in alveolar bone regeneration with statistical signigicant difference. In cementum regeneration, both the prepared glass and glass-ceramics showed significantly different effect. However, there were no statistical significant difference neither in glass nor glass-ceramics in the amounts of junctional epithelium migration and connective tissue adhesion. Further study is required to control the flowability as well as reduce the absorption rate in vivo.

Abstract: This study aimed to investigate the effects of hydroxyapatite on bonding strength between dental luting cement and human teeth. In the previous study, bonelike forming ability by mixing hydroxyapatite with several bone cements was reported in a protein-free acellular simulated body fluid with ion concentrations nearly equal to those of the human blood plasma. Therefore in this experiment, we assumed that if bonelike apatite layer could form between dental luting cement and human teeth, the bonding strength between the two would improve. In addition, we expected the HA mixed dental luting cement to improve the physical properties. Fuji I glass ionomer and Relyx™ glass ionomer cement were the selected dental luting cements and the film thickness, setting time and compressive strength were measured mixing various concentrations of hydroxyapatite. Glass ionomer cement with the most superior physical properties(Fuji I ; 20% hydroxyapatite, Relyx™ ; 15% hydroxyapatite) was immersed in the simulated body fluid for three weeks and the surface was observed under SEM after measuring the bonding strength. As the concentration of HA increased, the film thickness of hydroxyapatite-glass ionomer cement decreased, the setting time increased, and the compressive strength increased. The most noteworthy results were that bonding strength increased, and that bonelike apatite formed on the tooth surface when observed under SEM.

Abstract: Alkali oxides were added to glass frit in order to lower the firing temperature of dental porcelain, and the effects of Li2O and B2O3 on the thermal properties and chemical solubility of low-fusing dental porcelain were investigated. The glass transition temperature(Tg) and softening temperature(Ts) of glass frits were decreased remarkably by adding Li2O, but the coefficient of thermal expansion(CTE) was increased with Li2O. In the case of adding B2O3, the thermal properties were unchanged. Tg of B0L4, B2L4 and B4L4 specimens were lower than 500°C and Ts were lower than 550°C. The chemical solubility of prepared low-fusing dental porcelain with these glass frits were 37.3, 43.9, and 49.2µg·cm-2 respectively. The chemical solubility was increased by adding Li2O and B2O3, but all the results were below 100µg·cm-2 and satisfactory to ISO Standards. Further, the chemical solubility of the commercial low-fusing dental porcelains were 52.6µg·cm-2 for Ceramco Finesse(Clear), 70.8µg·cm-2 for Duceram-LFC(TC) and that of conventional dental porcelain, CeraMax(T-C), was 34.8µg·cm-2.

Abstract: Dental impression materials are used to register or reproduce the form and relationship of the teeth and oral tissues. They should not be torn when removing from the wet mouth after setting. Nowadays, silica is widely used as filler to overcome the low mechanical strength of the dental impression materials. The purpose of this study was to synthesize high strength glass in the system of MgO-CaO-Al2O3-SiO2 and investigate its usefulness according to ISO standard after mixing with addition silicone. Commercial products, Contrast, Examix, Express, and Perfect-F were selected as control group. When the prepared glass filler was introduced in addition silicone impression material, tear strength was drastically increased significantly than that of the control group, keeping the consistency. All experimental groups showed higher tear stength than that of control groups. As the amount of filler content increases, tear strength was increased. Strain in compression, recovery from deformation, and linear dimensional change were satisfied the ISO standard either all the experimental or control groups. Therefore, calcium-substituted magnesium aluminosilicate glass in the system of 12.5MgO-17.5CaO-20Al2O3-50SiO2 is expected the useful filler in the light body of addition silicone impression materials.

Abstract: This study evaluated periodontal repair and biomaterial reaction following implantation of a newly fabricated calcium phosphate block bone with chitosan membrane on the regeneration of 1-wall intrabony defects in the beagle dogs. The surgical control group received a flap operation only, while the experimental group I was treated with a chitosan nonwoven membrane only and the experimental group II was treated with a chitosan nonwoven membrane and a calcium phosphate block bone. The subjects were sacrificed 12 weeks after surgery and a comparative histometric analysis was done. No root resorption or ankylosis were observed in the experimental group. Mann-Whitney U test showed that the experimental group II produced statistically significant higher gain in connective tissue adhesion, new cementum regeneration and new bone formation. Based on histological results, the calcium phosphate block bone successfully functioned as a osteoconductive scaffold for invading cells of host.

Abstract: This study evaluated periodontal repair and biomaterial reaction following implantation of a newly fabricated calcium aluminate bony cement incorporating LiF-maleic acid on the regeneration of 1-wall intrabony defects in the beagle dogs. The surgical control group received a flap operation only, while the experimental group was treated with calcium aluminate bony cement incorporating LiF-maleic acid. The subjects were sacrificed 12 weeks after surgery and a comparative histologic analysis was done. In the experimental group, the grafted calcium aluminate cement was not absorbed and fibrous connective tissue was epithelized around the particles of the grafted bony cement. Because of certain favorable properties, such as its easy manipulation and its ability to maintain the morphology of the defect site by acting as a scaffold, the newly developed cement is suitable for us as a graft material, and could be used very effectively in alveolar augmentation. However, further study needs to be conducted before it can be used as a bone graft material for periodontal tissue regeneration.

Abstract: Cytotoxicity test was essential for the pre-clinical evaluation of bioceramics. Proliferation assays such as MTT, XTT and WST-1 were commonly used for measuring biocompatibility. WST-1 was more convenient than MTT because of its water-solubility and storage condition. The calcium phosphate glass and β-TCP have been used for bone substitute, and some magnetic ferrites have been used for hyperthermic treatment. L929, mouse fibroblast cell, was the representative cell-line for in vitro biocompatibility test. The extracts of test samples were prepared by ISO10993-12:2002. The biocompatibilities of the extracts were measured by MTT and WST-1 assay and their pH were measured with pH meter. The cellular survival rate of CPG was the lowest and the results of the WST-1 test showed results similar to those of the MTT test. Thus, proliferation assays using WST-1 may be conveniently and routinely applicable to pre-clinical evaluation of bioceramics.

Abstract: The effect of silica content in the PMMA/silica nano-composite on the mechanical properties and the growth behavior of apatite crystals were investigated. The PMMA/silica nano-composites with different silica content were synthesized through the sol-gel reaction with triethoxysilane end-capped PMMA and tetraethyl orthosilicate (TEOS). The compressive strength showed its maximum value when the content of TEOS was 20 wt% while the elastic modulus showed its maximum value when the content of TEOS was 60 wt%. The growth behavior of the apatite crystals following the cell culture showed different response according to the silica content. As increasing the TEOS content, the shape of the apatite crystals changed from globule-like structure to fiber-like one.