Papers by Author: Yong Keun Lee

Abstract: he aim of this study was to evaluate the effect of HA on the demineralization resistance and bonding strength of light-curing glass ionomer dental cement. Tests were conducted using (1) pure Fuji II LC GIC, (2) 15% micro HA-Fuji II LC GIC. Physical properties, demineralization resistance and bonding strength to dentin of teeth were determined. The curing depth in all groups were satisfied the requirement of curing depth of ISO 9917-2:2004(minimum curing depth = 1mm). The depth of cure was reduced with addition of HA, presumably due to the light scattering effect of HA particles. Regarding sensitivity to ambient light, there were no detectable changes of the homogeneity in any groups. Also all groups were satisfied the requirement of the flexural strength of ISO 9917-2:2004(minimum flexural strength = 20MPa). 15% HA-Fuji II LC GIC group was found to present a greater flexural strength than pure Fuji II LC GIC, as the addition of HA promotes a chemical reaction between the HA, the glass powder, and the polyacid. Observing under the CLSM after 4 days of demineralization, there were significant differences in the CLSM and SEM images. Pure Fuji II LC GIC group showed greater enamel demineralization layer than in 15% HA-Fuji II LC GIC group. In SEM analysis, there was greater enamel demineralization in the pure Fuji II LC GIC group, and less demineralized under the influence of HA particles, 15% HA-Fuji II LC GIC group had more even surface particles. 15% HA-Fuji II LC GIC group was found to present a greater bonding strength than pure Fuji II LC GIC group. Observing the fractured surfaces under SEM after the bonding strength test, the cohesive failure rate was found to be in increasing order of pure Fuji II LC GIC, 15% HA-Fuji II LC GIC group. There were bone-like apatite particles observed to be formed in 15% HA-Fuji II LC GIC group.

Abstract: We developed new calcium phosphate bone substitute material, amorphous calcium polyphosphate. The new material is synthesized by a cement-like slif-setting reaction with calcium phosphate glass, basic materials and water. In this study, we prepared with CPG, Na2CO3 and NaOH solution. When they are mixed together, amorphous phase was precipitated. The precipitated amorphous phase consisted of polyphosphate chains condensed with Na ions released from Na2CO3 and NaOH. When the amorphous calcium polyphosphate dissolves, inorganic polyphosphates are released into the medium. The inorganic polyphosphates as the dissolution product inducted the calcification of the osteoblast cells. Therefore, in animal test, the new bone formation in rat calvarial defects treated with the new material was significantly higher than sham-surgery control group, especially in the initial stage. The amorphous calcium polyphosphate was biocompatible and bioresorbable and promoted the new bone formation.

Abstract: This study aimed to evaluate the anticariogenic and remineralization effects of the glass ionomer dental luting cement containing nano-β-TCP in vitro. The β-Tricalcium Phosphate (β-TCP) are the components of dental enamel and bone mineral as biological apatites. In addition, β-TCP contains a significant amount of calcium and phosphate, which can promote remineralization of enamel subsurface lesions in animal and human. RelyXTM glass ionomer cement(3M/ESPE, USA) was used as dental luting cement. Film thickness, setting time, and compressive strength was measured for each group of pure glass GIC, 15% nano-β-TCP GIC. Human molars were prepared in box-shaped cavities that were filled with the GIC with and without the 15% nano-β-TCP were placed in 25ml of pH 5.0 acid buffer for 4 days at 37°C. After 4 days, longitudinal sections (1007m) were obtained through the center of each restoration. The sections were analyzed using a scanning electronic microscope (SEM) and confocal laser scanning microscopy (CLSM) to identify the change in the enamel surface. A significant difference in the CLSM images between pure GIC and nano-β-TCP-GIC. CLSM allows the demineralized surface layers of sound enamel to be visualized down to approximately 100 μm. The pure GIC specimens had a relatively thick fluorescent layer. On the other hand, the fluorescent layer of the nano-β-TCP-GIC specimens were thinner. The SEM images of micro surfaces demonstrate that nano-β-TCP-GIC is less rough than pure GIC. Therefore, the addition of nano-β-TCP enhanced protection against acid demineralization and promoted remineralization of enamel surface.

Abstract: The purpose of this study was to evaluate the osteogenesis of tetracycline blended chitosan membranes on the calvarial critical size defect in Sprague Dawley. An 8 mm surgical defect was created with a trephine bur in the area of the midsagittal suture. Forty rats were divided into four groups: negative control group, positive control group and two experimental groups. Three types of membranes were made and a comparative study was done. One type of non-woven membrane was made by chitosan for positive control. The other two types of non-woven membranes were made by immersing non-woven chitosan into either the tetracycline solution or the chitosan-tetracycline solution. Histologic analysis was done at 2 weeks and 8 weeks of healing periods. We concluded that that the use of tetracycline blended chitosan membrane on the calvarial defects in rats has a significant effect on the regeneration of bone tissue in itself. In addition it implicates that tetracycline blended chitosan membrane may be useful for guided tissue regeneration.

Abstract: This study evaluated periodontal repair and biomaterial reaction following implantation of a newly fabricated calcium phosphate chitosan block bone and chitosan membrane on the regeneration of 1- wall intrabony defects in the beagle dogs. The surgical control group received a flap operation only, while experimental group was treated with calcium phosphate chitosan block bone and/or chitosan membrane. All dogs were uneventful healing without any complication. The subjects were sacrificed 8 weeks after the experimental surgery, and a comparative histological and histometric examination was done. Chitosan membrane group significantly enhanced bone regeneration compared to control, CaP-chitosan block bone and combination group. Chitosan membrane remnants were observed in chitosan and combination group, while CaP-chitosan bone materials were resorbed completely. These results suggest that Chitosan membrnae significantly enhanced bone and cementum formation in advanced periodontal defects.

Abstract: The aim of this study was to evaluate the regenerative effects of chitosan membranes containing tetracycline (TC) applied to surgically created one-wall intrabony defects in beagle dogs. The defects either received chitosan membrane (CH), chitosan membrane containing 0.5%, 1% TC (CH-TC0.5, CH-TC1.0) or flap operation only. The animals were sacrificed 8 weeks after the experimental surgery, and comparative histological and histometric examinations were done. The amount of junctional epithelium migration and connective tissue adhesion did not show any statistically significant differences among the groups. The amount of new cementum regeneration, and new bone regeneration were significantly greater in CH-TC1.0 group than the control (P<0.05). The results suggest that chitosan membrane combined with 1.0% TC may have beneficial effect on the regeneration of bone and cementum in intrabony periodontal defects.

Abstract: The purpose of this study was to evaluate the effects of collagen membrane coated with PLGA on bone regeneration in rat calvarial defect. Five groups of 10 animals each received either collagen membrane coated with 0.5%, 1%, 3% concentration of PLGA, collagen membrane only or surgical control. Each group of animals was healed into 2 healing periods of 2(5 animals) and 8(5 animals)weeks and histologic and histomorphometric analysis were done. The results of the following study revealed that surgical implantation of collagen membranes coated with PLGA enhanced local bone formation at both 2 and 8 weeks independent of different PLGA concentrations. In conclusion, collagen membrane coated with PLGA shows a significant bone formation behavior irrespective of their concentration.

Abstract: This study examined the possibility of synthesis of biphasic calcium phosphate by sintering a mixture of hydroxyapatite and calcium phosphate glass. The effect of the concentration of calcium phosphate glass in a mixture on the proliferation and differentiation of MG-63 preosteoblast-like cells in a hydtoxyapatite scaffold was investigated. The addition of 5 wt% of calcium phosphate glass significantly improved the level of attachment, proliferation and differentiation of MG-63 cells onto the hydroxyapatite scaffolds, particularly when the surface was modified with 2% bovine serum albumin (p<0.05). Under these conditions, type I collagen was expressed and the extracellular matrix was formed by 1 week, and the ALP gene was expressed at 4 weeks.

Abstract: The purpose of this study was to evaluate histologically the effect of LiF-maleic acid added calcium aluminate (LM-CA) bone cement and calcium aluminate-polymethylmethacrylate (CA-PMMA) composite bone cement on bone regeneration in rat calvarial defect. After calvarial defects in 8 mm in diameter were created, three groups of 10 animals, a total of 30, each either received LM-CA bone cement, CA-PMMA composite bone cement or a sham-surgery control. Histologic analysis was done at 2 weeks and 8 weeks of healing periods. We concluded that LM-CA bone cement can be used as a bioactive bone graft material due to ability of bonding to the existing bone and CA-PMMA can be used as a graft material for augmentation of bone-volume due to dimensional stability.