Papers by Author: Kyoung Nam 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 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 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 composition of the electrolytes used in the process of anodic oxidation was modified to generate the novel anodic oxidation. The surface topography of the novel anodic oxidation showed that the pore/crater structures with the precipitants attached over the surface were observed in SEM. The physical properties and biocompatibility of the surface with the novel anodic oxidation were compared with that of anodic oxidation and machined surface of titanium. XRD, Bioactivity in a simulated body fluid, cell proliferation, and MTT test were performed to evaluate the differences among different surfaces.

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: 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.

Abstract: The aim of this in vitro study was to evaluate the tooth whitening effect of toothpaste containing nano-sized hydroxyapatite (HA). There were 3 types of dentifrices, which had a different level of abrasive components. For group 1, a newly developed toothpaste containing Nano-sized hydroxyapatite (Nano-HA) was used. Commercially available toothpastes were used in groups 2 and 3. Group 2 used toothpastes containing silica and multi phosphate. Group 3 used toothpastes containing abrasives with silica and micro-sized HA. In order to simulate 6-months of tooth brushing, the tooth specimens in all 3 groups were placed on a V8 Cross Brushing Machine (Sabri Co. U.S.A.) and brushed 10,000 times with the toothpaste slurries. The tooth specimens were then soaked in artificial saliva for 24 hours to create conditions similar to those encountered in vivo. The whitening efficacy was assessed before and after tooth brushing using the VITA shade scores of Shadeeye-EX NCC Dental Chroma meter (Shofu Co. Japan). All toothpastes produced significant differences in the mean shade change in the teeth before and after tooth brushing (p<0.05). However, there were no significant differences in the change in the shade between each group (p>0.05). Although the new Nano-HA toothpaste did not have superior whitening effects to the commercially available whitening toothpastes, they had a similar whitening efficacy to commercially available whitening toothpastes. These effects might come from the physical properties of Nano HA, which increase the surface dimension more than the Micro-sized HA and have the potential of remineralization.

Abstract: Hydroxyapatite is the main component of enamel that gives the tooth a bright white appearance and eliminates the diffused reflection of light by filling up the fine pores of the tooth surface. Accordingly, remineralization of the teeth can be expected to some extent if hydroxyapatite is used to treat an incipient caries lesion (early white spot lesion). In addition, the remineralization effect will be increased if the particle size of hydroxyapatite can be reduced to less than that of the micron-size in existing toothpaste preparations. The aim of this in vitro study was to evaluate the effect of nano-hydroxyapatite toothpaste, which was produced by nano-technology, on the remineralization of human enamel. A tooth specimen, on which artificial incipient caries had been induced, was immersed into two toothpaste slurries for remineralization. One contains nano-sized hydroxyapatite and fluoride, and the other contains nano-sized hydroxyapatite excluding fluoride. In order to evaluate the remineralization effect, the Vickers Hardness Number & SEM image of the enamel surface was evaluated at each step. There were significant differences in VHN values between those obtained before and after the remineralization steps. The results showed that the remineralization effect increased with increasing immersing time (P<0.05). However, there were no significant differences in VHN values between the two groups (P>0.05). SEM also demonstrated differences the in micro surface at each step. In conclusion, a toothpaste containing nano-sized hydroxyapatite has the potential to remineralize an incipient caries lesion. In addition, the addition of fluoride had no synergistic effect on remineralization.