Papers by Author: Kwang Mahn Kim

Abstract: The main objective of this study was to manufacture an oral rinse using the natural antibacterial agent (phytosphingosine, Doosan, Korea) for the prevention of periodontal disease and dental caries. Phytosphingosine is known to inhibit the growth of bacterial strains and induce apoptotic cell death in human cancer lines. In this study, antibacterial activity and cytotoxicity of oral rinses were performed with an experimental group containing phytosphingosine(PS) in vitro. Control groups consist of two Korean products and two American products containing chlorhexidine and cetylpyridinium chloride, respectively. There was no significant difference between experimental and control groups in the antibacterial activity and cytotoxicity except for Chika Chika Liq (p<0.05). According to the results, antibacterial activity of oral rinse containing PS was 99.62%, the strongest contact inhibition of Streptococcus mutans strain among tested groups. In the cytotoxicity test of oral rinses, PS had a weaker cytotoxicity than control groups in mouse and human normal cell lines and showed the strongest cytotoxicity in human oral cancer cell lines (KB cell). From the results, PS may be widely used as an oral rinse for the healthy and the patients with oral cancers in the near future.

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 titanium oxide layer with nano–micro hybrid structure on the titanium substrate was formed by grit-blasting and anodic oxidation treatment. A micro rough surface can be formed by grit-blasting and nanotube arrays can be formed by anodic oxidation or NaOH treatment after anodic oxidation. We investigated the surface characterization on titanium and the response of the osteoblast like cell (MG-63) to the surfaces made by different treatments. Surface structure (morphology), wettability characterized by SEM, contact angle. The attachment and proliferation behavior of MG-63 cells on the titanium surface by different surface treatments were characterized by SEM observation and MTT assay.The attachment and proliferation of osteoblast cells is accelerated by the topography of the nano structure like a nanotube, the nano surface acts as an attachment point for the filopodia of growing cells. Nano structure increases surface area and nano-micro structure significantly increases surface area. Such nano–micro hybrid structure on the titanium substrate can be useful for a well-adhered bioactive surface layer on Ti implant used metals for orthopedic and dental implants.

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: 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: This in vitro study compared the abrasivity of commercial desensitizing dentifrices with a sodium metasilicate (Na2SiO3) dentifrice using a Surface Profile Method. Dentin specimens were made from the root of extracted human molars. The cervical part of the teeth was sectioned with a diamond wheel disk. The teeth were embedded into an epoxy resin mold and the surface was gradually polished by silicone carbide paper. After grinding, the degree of surface roughness was tested within the range of 2 mm with tapping. The British Standard Institution reference dentifrice (BSI: CaCO3 40%) and experimental dentifrices (group 1: Na2SiO3 25%, CaCO3 10% and SiO2 10%, group 2: CaCO3 10% and SiO2 10%, group 3: CaCO3 10% and SrCl2 10%, group 4: Colloidal Silica 2-3% and Hydroxyapatite 10-20%) were evaluated. The dentifrice slurries were prepared by mixing 24 grams of the dentifrice in 12 ml distilled water. Each tooth specimen was brushed with the dentifrice slurries 1,000 times. The relative abrasivity of each dentifrice was evaluated from the ratio of the BSI standard dentifrice to each experiment. The results were analyzed by one-way ANOVA and Tukey’s multiple comparisons using Window SPSS (Statistical analysis system) 12.0. Groups 1 (71), 2 (74.2), 3 (38) and 4 (7.8) showed a lower abrasivity than the BSI dentifrice (100) (p<0.05). The relative abrasivity of groups 3 (38) and 4 (7.8) was the lowest compared with the BSI dentifrice (100). However, group 1 (71) containing Na2SiO3 showed a similar abrasivity to group 2 (74.2), which did not contain Na2SiO3 (p>0.05). Therefore, Na2SiO3 had no influence on the abrasivity of the dentifrice. In conclusion, the dentifrice containing Na2SiO3 had a lower abrasivity than the BSI reference dentifrice, but showed a significantly higher abrasivity than the existing commercial desensitizing dentifrices. Overall, the relatively high abrasivity of Na2SiO3 dentifrice is believed to be the result of other components in the abrasive system.

Abstract: The purpose of this study was to evaluate the shear bond strength of composite resin to 4 different all-ceramic coping materials with 3 different surface treatments after thermocycling and without thermocycling. Three different surface treatments - sandblasting with 50 ㎛ alumina particles (AB); sandblasting with 50 ㎛ alumina particles and acid etching with 4% hydrofluoric acid (AE); sandblasting with 50 ㎛ alumina particles and 30 ㎛ alumina particles with tribochemical silica coating (SI) and silane application - were used on four different all-ceramic; Feldspatic ceramic (Duceram Plus); Lithium disilicate ceramic (IPS Empress2); Alumica ceramic (In-Ceram Alumina); Zirconia ceramic (Zi-Ceram) - substrates. Shear bond strength of restorative composite resin to substrate was tested after thermocycling and without thermocycling (n=10). Each specimen was subjected to a shear load at a crosshead speed of 2 ㎜/min until fracture. Two-way analysis of variance and Duncan multiple comparison test (α =0.05) were used to analyze the bond strength values. There were significant differences in the bond strengths for ceramic types (P<.001), surface treatments (P<.001), and thermocycling (P<.001). The Duncan analysis showed that the Si specimens had significantly higher bonding strengths than other specimens. The bond strength of composite resin decreased after thermocycling.

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: The purpose of this study was to compare the bone regenerative effect of calcium phosphate glass according to the particle size in vivo. We prepared two different sizes, that is 400 μm and 40 μm, of calcium phosphate glass powder using the system CaO-CaF2-P2O5-MgO-ZnO. Critical-sized calvarial defects were created in 60 male Sprague-Dawley rats. The animals were divided into 3 groups of 20 animals each. Each defect was filled with a constant weight of 0.5 g calcium phosphate glass powder mixed with saline. As controls, the defect was left empty. The rats were sacrificed 2 or 8 weeks after postsurgery, and the results were evaluated using histological as well as histomorphometrical studies. The particle size of the calcium phosphate was crucial; 400 μm particles promoted new bone formation, while 40 μm particles inhibited it because of severe inflammation.