• Journal of the Korean Electrochemical Society
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• v.1 no.1
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• pp.1-7
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• 1998

For the purpose of finding new cathode materials for medium-temperature $(700\~800^{\circ}C)$ solid oxide fuel cells, $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3,\;(x=0.0\~0.5)$ are prepared, and their thermal stability and conductivity characteristics are investigated. Also, the cathodic activities are measured after the cathode layer being attached on CGO (cerium-gadolinium oxide) electrolyte disk. The X-ray analyses indicate that the materials prepared by calcining the citrate-gels at $800^{\circ}C$ have the orthorhombic perovskite structure without discernible impurities. The thermal stability of the undoped Co perovskite is so poor that it is decomposed to the individual binary oxide even at $1300^{\circ}C$. But the partially Fe-doped cobaltates exhibit a better thermal stability to retain their structural integrity up to $1400^{\circ}C$. The observation whereby both the undoped and Fe-doped cobaltates melt at ca. $1300^{\circ}C$ leads us to perform the electrode adhesion at <$1300^{\circ}C$. The cathodic activity of $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3,\;(x=0.0\~0.5)$, electrodes is superior to $La_{0.9}Sr_{0.1}MnO_3$, among the samples of $x=0.0\~0.5$, the x=0.2 cathode shows the best activity for the oxygen reduction reaction. It is likely that the Fe-doping provides a better thermal stability to the materials but in turn imparts an inferior cathodic activity, such that the optimum trade-off is made at x=0.2 between the two factors. The total electrical conductivity and ion conductivity of $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3$, are measured to be 51 S/cm and $6.0\times10^{-4}S/cm\;at\;800^{\circ}C$, respectively. The conductivity values illustrate that the materials are a mixed conductor and the reaction sites can be expanded to the overall electrode surface, thereby providing a better cathodic activity than $La_{0.9}Sr_{0.1}MnO_3$.

• The korean journal of orthodontics
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• v.26 no.2 s.55
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• pp.163-174
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• 1996

The purpose of this study was to examine the effects of bisphosphonate and indomethacin, blockers of bone resorption with different mechanisms, on alveolar bone remodeling. Male rats were divided into control, bisphosphonate and indomethacin groups, and then each group was divided info an experimental side and a control side according to the force application. Bisphosphonate(6.3mg/kg,$2.52x10^{-2}mol/L$) and indomethacin (9mg/kg, $2.52x10^{-2}mol/L$) were injected 6 hours and 1 hour before or 24 hours after the force application. The rats were killed 72 hours after the force application and histologic examination was perfomed. The values of serum acid phosphatase and lactate dehydrogenase were also measured in the control md experimental groups treated with bisphosphonate or indomethacin 1 hour before the force application. In the experimental side, the least number of osteoclasts was noted in the groups treated 1 hour before the force application with indomethacin or bisphosphonate, while there were no differences between the control and the groups treated with drugs 6 hours before or 24 hours after the force application. In the control side, the number of osteoclasts was not inecreased with no differences among the groups. Histologic examination revealed a severe alveolar bone resorption in the control group and the groups treated with indomethacin 6 hours before or 24 hours after the force application. Indomethacin treatment 1 hour before the force application and bisphosphonate treatment at any time significantly attenuated the bone resorption. Electron microscopically, ruffled border and clear zone of osteoclasts were observed in the control and indomethacin groups, while some osteoclasts were detached from the bone surface and exhibited dull cellular projections in the bisphosphonate groups. The bisphosphonate and indomethacin groups showed lower values of acid phosphatase and lactate dehydrogenase than the control group. The acid phosphatase value in the bisphosphonate group was lower than that in the indomethacin group, whereas there was no difference in the lactate dehydrogenase value between the groups. These results suggest that bisphosphonate reduces the activity of osteoclasts as well as the number of osteoclasts and that indomethacin reduces the number of osteoclasts without affecting the activity of osteoclasts. Bisphosphonate has a larger inhibitory effect on bone resorption md thus less limitation in the application time than indomethacin.

• The korean journal of orthodontics
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• v.26 no.2 s.55
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• pp.153-162
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• 1996

Rapid maxillary expansion is widely used for the correction of anteroposterior discrepancies, constriction of the maxillary arch, etc. This experiment was undertaken to examine the serial changes in the osteogenesis as well as the collagen fiber bundles in the intermaxillary suture during the rapid maxillary expansion treatment. Four young female dogs aged 6 to 8 months old and not showing menarche yet were used for the experiment. The maxillary impression of dogs were taken, expansion device cast and Hyrax screw soldered at the midline in the 1st premolar area. RME device was delivered to the dogs and the activation of 0.25 mm per quarter-turn was done 2 times per day for 10 days until 5 mm separation was made. Separation of the maxilla was confirmed by X-ray. The animals were sacrificed on 0, 15, 30, 60 days from the finish of maxillary separation and preparations for light microscopy and surface electron microscopy were made. The sutures were cut into frontal serial sections for examination of the histological reactions. The following results were obtained and the conclusions made. 1. The edges of the two palatal plates bordering the midpalatal suture which at the beginning of the retention period were mainly composed of compact bone, underwent extensive resorption followed by new bone formation and gradually became spongy bone rich in bone marrow which in the 60 day retention animal became the compact bone with short intermaxillary suture space. During this transformation, newly formed trabecular bone tissues were added to the original margin. 2. Throughout the expansion period, the collagen fibers underwent successive changes such as stretching, loss of polarity, and finally fibrillogenesis. Towards the end of the expansion procedure, sharpey's fiber formation in newly formed bones were observed. 3. Bony spicules were found in the initial stage of retention on occlusal topographic X-rays, which later were confirmed to have ossified. 4. Judging from the histological changes occuring during the experimental expansion, excessive expansion will cause an excessive bleeding, and retard the remodeling of intermaxillary suture. According to the above results, the bone remodeling after rapid maxillary expansion was preceded by the migration of migratory cells into the intermaxillary suture area. The bone remodeling phenomena were on-going during the 2 months retention sample.

• Journal of Oral Medicine and Pain
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• v.30 no.2
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• pp.269-276
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• 2005

This in vitro study evaluated the influence of a flowable composite resin on the tensile bond strength of resin to enamel and dentin treated with Er:YAG laser and diamond bur. 96 Buccal enamel and mid-coronal dentin were laser-irradiated using an Er:YAG laser and treated with diamond bur. Each groups(48) were divided two small groups depends on acid-etching procedure. Light-cure flowable resin(Metafil Flo) and self-cure resin(Clearfil FII New Bond) were used in this study. After surface etching with 37% phosphoric acid and the application of an adhesive system, specimens were prepared with a hybrid composite resin. After 24hours storage in distilled water at 37$^{\circ}C$, all samples were submitted to the tensile bond strength evaluation, using a universal testing machine(Z020, Zwick, Germany). The obtained results were as follows: 1. TBS of acid-etching group were higher than those of non-etching group in both enamel and dentin treated with Er:YAG laser and diamond bur. Laser 'conditioning' was clearly less effective than acid-etching. Moreover, acid etching lased enamel and dentin significantly improved the microTBS of M-Flo. 2. In enamel, TBS of laser-irradiated group were lower than those of bur-prepared group. However, in flowable resin subgroup, there were not differed those between two groups in dentin. 3. In laser-treated group, TBS of flowable composite resin were higher than those of self-curing resin in dentin, however, there was no difference in enamel. From this study, we can conclude that the self- and light-cure composite resin bonded significantly less effective to lased than to bur-cut enamel and dentin, and that acid-etch procedure remains mandatory even after laser ablation. We suggest that Er:YAG laser was useful for preparing dentin cavity with flowable resin filling.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.2
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• pp.158-175
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• 2005

Statement of problem. Every effort has been continually made to obtain objectivity in measuring the longevity of fixed restorations, such as by establishing unified judgement standard for deciding success and adopting statistical method that analyzes the data of successful and failed cases at the same time. In Korea, however desired level of development has not to be made in this field yet. Purpose. This study, adopting California Dental Association (CDA) quality evaluation system, established objective standard for deciding success, and inferred the longevity of fixed restorations and their failure analysis through adopting Kaplan-Meier survival analysis. Material and method. In order to assess the longevity of flxed restorations serviced in Korea and causes of failure, a total of 1109 individuals (aged 15-74, 716 women and 393 men loaded with 2551 unit fixed restorations, and 1934 abutments) who lived in Kyung-In Province were examined and the findings were as follows : Results. 1. Length of service of fixed restorations serviced in Korea was 6.86$\pm$0.15 yr (mean), 5.5 yr (median), and the rate of success was 65.82% in 5 year survival, and 21.15% in 10 year survival. 2. When there was patient's need for replacing old prosthetics, longevity of fixed restorations was 7.51$\pm$0.27 yr (mean), 7 yr (median), and the rate of success was 61.08% in 5 year survival, and 17.57% in 10 year survival. 3. Longevity of fixed restorations was longest in the over-sixty age group(9.21$\pm$0.66) and that of the teen age group(3.39$\pm$0.28) was shortest (p<0.05). 4. Longevity of fixed restorations of women (7.38$\pm$0.18 years) was longer than that of men (6.00$\pm$0.26) (p<0.05). 5. As for the provider factor (such as unlicensed performers, university hospitals, and private clinic), there was no statistically significant difference in longevity of fixed restorations. 6. Defective margin (34.78%). periodontal disease (12.15%), periapical involvement (11.73%), was the most frequent causes of failure and poor esthetics group showed the longest life above all (p<0.05). Actual frequent causes of failure after removing old prosthetics were defective margin, periapical involvement, periodontal disease and uncemented restoration. In 75.67% of the cases, abutment state after removing old prosthetics was good enough for loading another prosthetics. 7. There was found to have statistically significant influence between longevity of single crown (6.35$\pm$0.20 yr) and that of 3 unit fixed restorations (7.60$\pm$0.30 y) (p<0.05). In each case the most frequent cause of failure was defective margin. 8. The number of cantilever pontic, pontic/abutment ratio, oral hygiene status were found to have no statistically significant influence on longevity of fixed restorations in all groups (p>0.05). 9. Longevity of fixed restorations made of non precious metal was longest (9.60$\pm$0.40 yr) semi precious and precious trailing behind(p<0.05). 10. Group function group (37.04%) and partial group function group (44.62%) were predominant in frequency but showed no correlation between them and among different types of occlusal plane and different types of occlusal surface (p>0.05). 11. Longevity of fixed restorations was longest in the centric interference group(9.35$\pm$0.62) (p<0.05) among different types of occlusal interference. Conclusion. We found that longevity of fixed restorations serviced in Korea is affected by age, gender and type of material, and that most frequent cause of failure is defective margin. In order to assess the accurate longevity of axed restorations, unified research design. overcoming inter-observer difference and establishing the objective research items are needed. Furthermore, it is thought that prospective approach through thorough study and regular follow-ups is needed just from the start of research. Nationwide detailed studies on length of service of fixed restorations manufactured in Korea are hoped to be conducted hereafter.

• Journal of Periodontal and Implant Science
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• v.23 no.3
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• pp.577-594
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• 1993

The ultimate goal of periodontal therapy is the regeneration of the periodontium that have been destroyed as a result of periodontal disease. This study were done in order to determine the healing status of periodontium under Polytetrafluoroethylene and millipore fillter combined with fibrin and the effect of the guided tissue regeneration procedures were performed as follows : 1) flap operation using PTFE membrane(control group) 2) flap operation using PTFE membrane which was fixed with fibrin(experimental group 1) 3) flap operation using millipore filter which was fixed with suture(experimental group II) 4) flap operation using millipore filter which was fixed with fibrin(experimental group II) After 1, 2, 4, 8, 12 weeks, dogs were sacrificed by perfusion technique and tissue block was excised including the tooth and prepared for light microscope with H-E & Masson’s trichrome staining. The result were as follows : In control and experimental group, there is no siginificant difference on epithelial cell down growth within 1st week, but more epithelial cell downgrowth in millipore or millipore combined with fibrin group. In this experiment, there were no significant difference in new cementum and alveolar bone formation whether PTFE membrane was fixed with suture or fibrin. In control and each experimental group, bone maturation appeared in 4 weeks, bone width increased bucco-lingually in control and experimental 1 group especially. Both control group and experimental group showed mild mew cementum formation on root surface and irregular arrangement of collagen fiber at 4 weeks, that showed obvious increased cementum formation at 8 weeks, and that was observed the functional arrangement of collagen fiber between new cementum and new alveolar bone at 12 weeks.

• Journal of the Korean Society of Food Science and Nutrition
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• v.46 no.4
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• pp.459-464
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• 2017

Biphenyl is used as an intermediate in the production of crop protection products, a solvent in pharmaceutical production, and as a component in the preservation of citrus fruits in many countries. Biphenyl is not authorized for use and also does not have standards or specifications as a food additive in Korea. National and imported food products are likely to contain biphenyl. Therefore, control and management of these products is required. In this study, a simple analytical method was developed and validated using HPLC to determine biphenyl in food. These methods are validated by assessing certain performance parameters: linearity, accuracy, precision, recovery, limit of detection (LOD), and limit of quantitation (LOQ). The calibration curve was obtained from 1.0 to $100.0{\mu}g/mL$ with satisfactory relative standard deviations (RSD) of 0.999 in the representative sample (orange). In the measurement of quality control (QC) samples, accuracy was in the range of 95.8~104.0% within normal values. The inter-day and inter-day precision values were less than 2.4% RSD in the measurement of QC samples. Recoveries of biphenyl from spiked orange samples ranged from 92.7 to 99.4% with RSD between 0.7 and 1.7% at levels of 10, 50, and $100{\mu}g/mL$. The LOD and LOQ were determined to be 0.04 and $0.13{\mu}g/mL$, respectively. These results show that the developed method is appropriate for biphenyl identification and can be used to examine the safety of citrus fruits and surface treatments containing biphenyl residues.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.2
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• pp.207-220
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• 2006

The newly developed equipments for the early detection of carious lesion are LFD (laser fluorescence device), Ultrasonic diagnostic system, CLSM(confocal laser scanning microscopy), QLF(quantitative light-induced fluorescence) and DIFOTI (digital imaging fiber-optic trans-illumination) system. In this study, DIFOTI system and LFD were used for the detection of early enamel caries. Twenty five primary teeth extracted from twenty one children at around the dentitional exchanging period were selected as samples. The results obtained from DIFOTI imaging and LFD measurement were compared with those of CLSM and comprehensive evaluations were made for the diagnostic capacity of each device. In vitro test, 40 sample teeth with their buccal & lingual surface formed by a window of $2{\times}3mm$ in diameter were immersed in artificial demineralizing solution for the period of 4, 8, 12 and 16 days. The results obtained from the experimental groups (DIFOTI, LFD) were compared to control group (CLSM) and we have reached to the following conclusions. 1. The sensitivity and specificity of DIFOTI system operated in oral environment was 88.2% and 76.9% respectively. 2. The sensitivity and specificity of LFD measured in oral environment was 76.5% and 69.2% respectively. 3, Regression analysis on the light transparent rate of DIFOTI showed its decrease according to the length of primary enamel decalcification performed in vitro(r=-0.96, p<0.05). 4. No statistically significant difference between LFT measurement and the length of in vitro decalcification was found in regression analysis (p>0.05). 5. The correlation coefficient of DIFOTI image transparent rate and the lesion depth of CLMS was -0.6988 (p<0.05), whereas no statistically significant difference was found for LFD measurement.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.2
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• pp.233-243
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• 2006

The aim of this study was to investigate the relationship between the C-factor and shrinkage strain values of composite resin and examine the strain values in different incremental filling techniques. Experiment consisted two aims. First, we compared with strain value in two different C-factors(3.7 and 1.0). Second, we examined the strain values in three different filling techniques. The results of the present study can be summarized as follows : 1. High C-factor groups showed higher contraction stress values than low C-factor groups at 900 sec after polymerization. 2. Hybrid resin showed higher contraction stress values than flowable resin in high C-factor cavities. But contraction stress was not revealed significant difference between hybrid resin and flowable resin in low C-factor cavities (P>0.05). 3. Bulk felling with hybrid resin(Group 1) showed high contraction stress and lining with flowable resin followed hybrid resin (Group 5) showed lower contraction stress. 4. Contraction stress were increased during 900 sec after polymerization in high C-factor groups but decreased gradually after 900 sec. 5. Low C-factor groups showed tight marginal seal between resin and cavity wall but high C-factor groups showed gaps formed between resin and cavity wall in part. On the basis above results, layering techniques in high C-factor cavity showed advantages in reducing contraction stress and gap formation between cavity wall and resin restoration.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.4
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• pp.554-562
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• 2003

Xylitol has been used as sugar substitute to prevent dental caries. It is not fermented by most dental plaque bacteria and interferes with the growth of mutans streptococci. Therefore the production of acidic metabolites and the growth of mutans streptococci are inhibited. S. mutans strains which are inhibited to grow under the presence of xylitol are referred as xylitol-sensitive ($X^S$) strains. However, experimental and clinical studies have shown that there were mutated groups of S. mutans strains that are not affected by xylitol. They are referred as xylitol-resistant($X^R$) strains. The aim of the present study was to investigate that emergence of $X^R$ strain would effect on the anticariogenecity of xylitol by comparing the growth rate, the extracellular pH, hydroxyapatite adhesion and the agglutination of the $X^R/X^S$ strains. Overall we came out with following results : 1. No difference in the growth rate and the extracellular pH was found between the $X^S$ strain and the $X^R$ strain. 2. No difference in adhesion to hydroxyapatite surface was found between the $X^R$ strain and the $X^S$ strain (p>0.05) and adhesion of the $X^S$ strain was greater than that of $X^R$ strain in the sucrose-dependent adhesion to hydroxyapatite (p<0.05). 3. The $X^R$ strain was agglutinated in the lower concentration of saliva than that of $X^S$ strains.