Papers by Author: Sang Bae Lee

Abstract: The 2% NaF and 8% SnF2 have been used in topical fluoridation method in the dental office to increase the resistance of enamel to acid dissolution. Bis-GMA based monomers have been used for the basic materials in the dental pit and fissure sealants. Therefore, the resinous pit and fissure sealant including fluorides may increase the effect of preventing dental caries. In this study, we made a novel dental pit and fissure sealant and evaluated some properties, especially fluoride release. In order to make experimental pit and fissure sealant including fluoride, NaF and SnF2 powder were added into self-made monomer composed of Bis-GMA, TEGDMA, UDMA and photo initiator system by weight percent of 2% and 8% respectively. The just monomer without fluoride powder was used for control. Uncured film thickness and depth of cure were measured according to ISO specification 6874:1988 and the viscosity was measured using rheometer. The five disc specimens were made using light curing unit to evaluate fluoride releasing and each specimen was immersed in the artificial saliva of 10 mL. Fluoride ion concentrations in extracts were measured for 3 days using fluoride electrode at every 12 hrs. There was no significant difference between experimental and control group in the depth of cure, uncured film thickness, and viscosity (p>0.05). The released fluoride ion concentration was continuously retained for 72 hrs.

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: In this study, the antibacterial effects of glass ionomer cement containing silver-zeolite were evaluated. New antibacterial glass ionomer cements with silver-zeolite were prepared as follows. Silver-zeolite (1, 3, and 5 wt%) was incorporated into the glass ionomer cement powder and then mixed with the polyacidic liquid at the ratio recommended by the manufacturer. Agar diffusion test was used to evaluation of antibacterial effect. Setting time, film thickness and compressive strength were also determined. Paired samples t-tests and ANOVA were used, and P<0.05 was considered significant. Film thickness and setting time were increased dependent on the amount of silver-zeolite. Glass ionomer cement with 1 wt% of silver-zeolite seemed to increase the compressive strength. However, increasing ratio of compressive strength was diminished beyond 3 wt%. Glass ionomer cements containing silver-zeolite have been successfully demonstrated to have antimicrobial effects on S. mutants in vitro. These results indicate that glass ionomer cement containing silver-zeolite have the potential to enhance antibacterial of dental cement in oral cavity.

Abstract: The antibacterial brushite-forming calcium phospahte cements (CPC) were prepared using an equimolar mixture of β-tricalcium phosphate (β-TCP) and monocalcium phosphate monohydrate (MCPM) with chlorine dioxide (ClO2) generating powders (sodium chlorite and mixed acid activator). The effect of ClO2 on cement setting time, compressive strength, and antibacterial property of novel antibacterial CPC was investigated. The use of 0.3M citric acid solutions as liquid phase enabled final setting times of 5~10 min. The setting time of antibacterial cement systems was prolonged with increasing the amount of antibiotic used. Dry compressive strength was found to be in the range between 9~15 MPa and increased with addition of ClO2 generating powders. Wet compressive strength was slightly decreased compared to dry compressive strength after immersion of cement samples in water for 24 h. The antimicrobial potency of the different cement formulations was investigated using the agar diffusion method. The acidic brushite cement itself showed the inhibitory effect for Streptococcus mutans. The inhibition zone was increased with the amount of ClO2 generating powders. These results indicate that our novel antibacterial CPC have the great potential to avoid the development of infections for preventive antibiotic therapy.

Abstract: In this study, the effect of cyanoacrylate-based β-tricalcium phosphate (β-TCP) on pullout strength of orthodontic mini-screw was evaluated. New cements were prepared by mixing Histoacryl® (n-butyl cyanoacrylate) and acid-treated β-tricalcium phosphate. The ratios of β-TCP to Histoacryl® were 0, 0.5, 1.0, and 2.0. Artificial bone blocks were used as a substrate for the miniscrew implantation. The test groups were divided into three groups (one solid bone block [group 1] and a bone block with a 0.9 mm hole [group 2], and a bone block with a 2.5 mm hole [group 3]). And each group was divided into subgroups according to cement usage and non-usage. The used artificial bone density was 0.64g/cm2. Pullout strengths were determined using a universal testing machine. Statistical analysis was performed using the SPSS 9.0 for Windows program. Paired samples t-tests and ANOVA were used with p<0.05. The maximum pullout strengths were 295.9 ± 3.8 N for group 1, 261.1±15.0 N for group 2, and 273.2±20.0 N for group 3. In group 1 and 2, the pullout strength in the subgroup using cement was higher than that of the subgroup of not using cement (p<0.05). In group 3, the pullout strength in the subgroups using cyanoacrylate-based β- TCP cement was higher than that of the subgroup using conventional glass ionomer cement (GC Fuji-I, GC Co., Tokyo, Japan) (p<0.05). These results indicate that our β-TCP/Histoacryl® cements have the potential to enhance pullout strength of the orthodontic mini-screw.

Abstract: In this study, the effects of bracket designs and force direction on fracture strength of alumina bracket were evaluated. Two differently designed alumina brackets (MISO, HT Co., Ltd., Seoul, Korea) were tested. Each bracket was bonded with orthodontic adhesive to stainless steel cylinder. Compressive force was applied to the tie wing of bracket at 30°, 60°, and 90° to the long axis of the test device. Fracture strengths were assessed by using a universal testing machine (Instron 3366, Instron Co., Ltd., U.S.A.). Fractured bracket surfaces were examined using SEM. Statistical analysis was performed by using SPSS 9.0 for Windows program. Paired samples t-tests and Kruskal-wallis tests were used at P<0.05. The fracture strength ranged from 150 N with the occlusal wing to 63 N with the cervical wing in bracket A. A significant difference was founded in fracture strength between the bracket designs and force directions. Based on this result, it could be concluded that bracket designs and force direction was important rule to improve fracture strength of ceramic bracket.

Abstract: Histoacryl® (N-butyl-2-cyanoacrylate) has been widely utilized as a tissue adhesive. The aim of this study was to evaluate the physical and adhesive properties of newly developed cyanoacrylate-based β-TCP composite systems. The β-TCP powder was modified on the surface with citric acid to make this material mixed with cyanoacrylate easily. The setting time of acidtreated β-TCP/ Histoacryl® systems was dramatically prolonged and the polymerization heat was significantly decreased compared to that of untreated β-TCP/Histoacryl® system. The shear bond strength of cyanoacrylate-based β-TCP composites decreased with addition of acid-treated β-TCP filler. The compressive strength of β-TCP/Histoacryl® composites increased strongly with increasing the amount of acid-treated β-TCP filler. The cytotoxicity of the β-TCP/Histoacryl® composites decreased with the increasing of the amount of added β-TCP. These results indicated that our novel β-TCP/Histoacryl® composites had the great potential to serve as adhesives or filling materials in the dental field.

Abstract: In this study, the osteoconductive properties of novel cyanoacrylate-based filling materials for bone defect were evaluated. A new filling material was prepared by mixing Histoacryl® and acid-treated
-tricalcium phosphate (
-TCP). Mixing weight ratio of acid-treated
-TCP to Histoacryl® was 5:1. 12 male Spraque-Dawley rats were used in this study. The animals were divided into 4 groups. Critical-sized calvarial defects (8 mm) were created in 9 animals, and then the defects were treated with dense pellet specimen, porous cement-like specimen, and untreated defect for surgical control group. Augmentation treatments were carried out in 3 animals. Histological analysis revealed excellent ostgeoconductive properties of new filling materials. But, some of
-TCP particle in the cement-like group were encapsulated by fibrous connective tissue. For the dense pellet group and augmentation treatment group, shape and stability were better maintained during the implantation time than cement like group. These results indicate that our novel
-TCP/Histoacryl® composite have the potential to serve as filling materials for bone defects in the dental and plastic surgery.

Abstract: The formation of titanium oxide layer with micro and nanotube arrays on titanium substrate was investigated by grit-blasting and anodic oxidation treatment. Micro rough surface can be formed by grit-blasting and nanotube arrays can be formed by anodic oxidation. The morphology of the hybrid surface(micro and nanotube arrays surface) can be affected by the mechanical conditions (grit size, grit material, blasting pressure, nozzle tip of blasting machine, distance nozzle tip and specimen, blasting time) and electrochemical conditions (applied potential, electrolyte concentration and anodizing time) used. Such micro pore and nanotube arrays of titanium oxide can be useful for well-adhered bioactive surface layer on Ti implant metals for orthopedic and dental implants, as well as for photo catalysts and other sensor applications.

Abstract: We tried to prepare a new filling material for bone defects using β-Tricalcium phosphate (β-TCP) particles and Histoacryl®. The aim of this study was to evaluate physical and bioactive properties of cyanoacrylate-based filling materials for bone defects in the dental field. The shear bond strength values of the Histoacryl® and β-TCP/ Histoacryl® compounds stored in double-distilled water decreased with the increase of the amount of added β-TCP. The temperature change of the β-TCP/ Histoacryl® compounds during polymerization decreased compared to that of the Histoacryl®. The cytotoxicity of the filling materials decreased when the amount of added β-TCP was increased. In the evaluation of bioactivity, hydroxyapatite (HA) was precipitated on the surface and inner space of the porous filling material 4 weeks after immersion in SBF. This precipitation of HA on the surface of the filling material was also confirmed in the XRD result. These results indicate that our novel β-TCP/Histoacryl® compounds have the potential to serve as filling materials for bone defects in the dental field.