• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.1
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• pp.92-99
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• 2002

There have been efforts that inhibit development of dental caries by sugar substitution. But, it is controversial if xylitol has anticariogenic effect in the presence of sucrose. And there are few papers dealing with the combined action of xylitol and sucrose. For the purpose of resolving this controversy, the author investigated the effect of xylitol on enamel demineralization and on adhesiveness of S. mutans to hydroxyapatite in the presence of sucrose. Five experimental solutions were prepared as follows: (S: sucrose, X: xylitol) Group 1: BHI broth Group 2: BHI+1% S Group 3: BHI+0.75% S+0.25% X Group 4: BHI+0.5% S+0.5% X Group 5: BHI+0.25% S+0.75% X Group 6: BHI+1% X Each solution was inoculated with $100{\mu}l$ of S. mutans JC-2. And saliva coated hydroxyapatite beads were put into each experimental solution. And then each solution was incubated at $37^{\circ}C$ under anaerobic condition. After incubation, the adhesiveness of S. mutans on hydroxyapatite was evaluated. The Vickers hardness numbers were measured on extracted human primary teeth, and these teeth were dipped into the same experimental solution and incubated at $37^{\circ}C$ under anaerobic condition for 48hours. Surface microhardness were measured again after incubation. The obtained results were as follows; 1. In the presence of sucrose, xylitol can reduce the adhesiveness of S. mutans on hydroxyapatite surface from the ratio of 25% sucrose to 75% xylitol(P<0.05). 2. In the presence of sucrose, xylitol can reduced demineralization of primary teeth enamel surface from the ratio of 50% sucrose to 50% xylitol(P<0.01).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.5
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• pp.229-234
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• 2017

In this study, TiAl alloy was fabricated by a centrifugal casting method for turbo charge of automotive. Optimum conditions for defectless morphology using various ceramic mold were investigated. The crystal structure, microstructure, and chemical composition of the TiAl prepared by centrifugal casting were studied by X-ray diffractometer (XRD), optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS), microvickers hardness analyzer (HV). Two kinds of dendrite structures were observed with 4-fold and 6-fold symmetries. The FE-SEM, EDS and HV examinations of the as-cast TiAl showed that the thickness of the oxide layer (${\alpha}$-case) was typically less than $50{\mu}m$.

• Journal of Korean society of Dental Hygiene
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• v.12 no.3
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• pp.533-541
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• 2012

Objectives : The purpose of this study was to evaluate the effects of tooth bleaching agent contained 35% hydrogen peroxide on the color, microhardness and surface roughness of tooth-colored restorative materials. Methods : Four types of tooth-colored restorative materials, including a composite resin(Filtek Z350 ; Z350), a flowable composite resin(Filtek P60 : P60), a compomer(Dyract$^{(R)}$ AP ; DY), and a glass-ionomer cement(KetacTM Molar Easymix ; KM) were used in the study. The specimens($8mm{\times}5mm$) were made by using a customized acrylic mold. Each material was divided into two groups equally(n=40) : experimental group(35% HP) and control group(distilled water). 35% HP group was treated 30 mim/5 days for 15 days. Each 30 minute treatment session consisted of two 15 minute cycles of gel application with 20 second light exposure. The authors measured the color, microhardness, and roughness of the specimens before and after bleaching. The data were analyzed with ANOVA and T-test. Results : 35% HP group showed an apparent color change(${\Delta}E^*$) than control group. In particular, DY and KM showed a noticeable color change and statistically significant differences(p<0.05). 35% HP group showed a reduction in microhardness. Z350 and P60 does not have a statistically significant difference(p>0.05), DY and KM showed a statistically significant difference(p<0.05). Percentage microhardness loss(PML) of control group was 0.6 to 5.5% in the group, 35% HP group was 6.6 to 34.6%. Roughness was increased in 35% HP group after bleaching. Especially DY and KM were significantly increased(p<0.05). Conclusions : Bleaching agents may affect the surface of existing restorations; therefore, they should not be used indiscriminately when tooth-colored restorations are present.

• Journal of dental hygiene science
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• v.8 no.4
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• pp.255-260
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• 2008

The purposes of this study were to examine the effect of 35% hydrogen peroxide (HP) bleaching agent on the changes in physical and chemical characteristics of tooth. The bleached teeth showed an apparent color changes. The whiteness increased linearly within the tested period as the period of bleaching increased. The microhardness between bleached groups after bleaching showed any statistically significant difference according to the paried t-test. The bleached enamel surface showed any apparent morphological changes compared to the enamel which was stored in distilled water only. The difference of the total mineral contents for the distilled water and hydrogen peroxide did not show statistical significance. These results demonstrated that bleaching using 35% hydrogen peroxide were adversely affects application time of experimental group and may confirm the safety of using these agents for a short time in dentist-monitored bleaching.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.3
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• pp.365-376
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• 2006

The purpose of this study was to evaluate the efficacy of blocking the oxygen in the air during the polymerization of sealant. All curing were performed with various light curing units under the application of oxygen gel barrier, stream of nitrogen and carbon dioxide gas for inhibition of oxygen diffusion into sealant surface. The results of present study can be summarized as follows : 1. The amount of eluted TEGDMA form the specimens cured with all the three different light units in the stream of $N_2$ and $CO_2$ gas and application of Oxygen gel barrier($DeOx^{(R)}$) were significantly lower than in the room-air atmosphere (Control) (p<0.05). 2. In the $DeOx^{(R)}$ application, the amount of eluted TEGDMA the specimen cured with PAC light for 10seconds was less than that cured in the stream of $N_2$ and $CO_2$ atmospheric conditions (p<0.05) 3. In the LED using 10 or 20sec irradiation times under the stream of $N_2$ and $CO_2$, the eluted TEGDMA showed to be no statistically significant difference (p>0.05). 4. The microhardness from the specimens cured with all the three different light units under each treated conditions were significantly higher than in the room-air atmosphere (p<0.05). 5. The surface treatment by $DeOx^{(R)}$, $N_2$ and $CO_2$ reduces the thickness of oxygen inhibited layer by sp proximately 49% of the untreated control value.

• Journal of the korean academy of Pediatric Dentistry
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• v.44 no.2
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• pp.170-179
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• 2017

The purpose of this study was to compare the cariogenicity of commercially available bovine milk and low-fat milk in a biofilm model using the CDC Biofilm Reactor. Streptococcus mutans ATCC 25175 biofilms were formed on saliva coated bovine enamel slabs in a CDC Biofilm Reactor. Biofilms were exposed three times per day to one of the following materials: commercial whole milk (fat content: 3.4%), low-fat milk (fat content: 1%), or 0.9% NaCl. Medium pH was measured at different time points. After 5 days, biofilms were separated from slabs to evaluate the CFUs. The biofilm thickness was observed by confocal laser-scanning microscopy (CLSM). Enamel slab's demineralization was assessed by measuring surface microhardness before and after the experiment. For microhardness and CFUs assessment, no significant difference was found among the three groups. All groups showed similar pattern of medium pH change and biofilm thickness. Our results showed that there was no difference in the cariogenicity between whole milk and low-fat milk. Both milks were relatively non-cariogenic compared to the control group.

• Journal of dental hygiene science
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• v.11 no.5
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• pp.397-404
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• 2011

The aims of this study were to evaluate the effect of native acidity upon dental hard tissues by measuring pH in mouth-rinse, which is on the market, and to evaluate even influence of dental stain caused by mouse-rinse given using for a long time. The experimental group was used Garglin, Nextcare, Listerine, and Hexamedin. The control group was used sterile distilled water. As a result, pH was indicated to be low in Nextcare(4.70) and Listerine(4.16). In a change of color tone, $b^*$ value of indicating Yellow-blue showed the lower value than the early color tone in all groups. There was statistical significance in Nextcare and Listerine. ${\Delta}L^*$ value of indicating light -dark gets darker after using Nextcare, Listerine and Hexamedine. A change(VHN) in surface hardness of enamel showed reduction in surface hardness after 14 days in Nexcare and Listerine. As a result of confirming a change in enamel surface by using Scanning Electron Microscopy, the erosion aspect on the enamel surface could be confirmed in groups of Nexcare and Listerine. Ra value in surface roughness of enamel could be observed the enamel surface, which got rougher compared to other experimental groups.

• Journal of the Korea Convergence Society
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• v.8 no.6
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• pp.139-145
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• 2017

The aim of this study was to measure the remineralization effect of APF gel and fluride varnish on artificial enamel caries using CLSM in vitro. The samples were divided into 3 groups: control, 1.23% APF gel, 5% NaF varnish. The specimen surfaces were observed by CLSM and measured average fluorescence of the lesion(AFL). The results were analyzed using one-way ANOVA and Pearson's correlation analysis at a significance level off 0.05(PSWA 18.0, SPSS Inc., USA). There were significant differences between AFL at baseline and 1 day after fluoride application(p<0.05) but there are no significant differences between ${\Delta}$ AFL of all groups (p=0.222). Result of Pearson's correlation analysis, there are no significant correlation between VHN and AFL, but there were significant correlation between AFL at baseline and 1 day after fluoride application(r=0.811, p<0.001). Although AFL decreased after fluoride application, but there was no difference between the groups. In the future, it is necessary to test the oral environment model or in situ experiment supplemented the limitations of this study.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.317-318
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• 2012

현재의 반도체 산업에서 Hafnium oxide와 Hafnium silicates같은 high-k 물질은 CMOS gate와 DRAM capacitor dielectrics로 사용하기 위한 대표적인 물질에 속한다. MOSFET (metal oxide semiconductor field effect transistor)구조에서 gate length는 16 nm 이하로 계속 미세화가 연구 중이고, 또한 gate는 기존구조에서 Multi-gate구조로 다변화가 일어나고 있다. 이를 통해 게이트 절연막은 그 구조와 활용범위가 다양해지게 될 것이다. 동시에 leakage current와 dielectric break-down을 감소시키는 연구가 중요해지고 있다. 그러나 나노 영역에서의 기계적 특성에 대한 연구는 전무한 상태이다. 따라서 복잡한 회로 공정, 다양한 Multi-gate 구조, 신뢰도의 향상을 위해서는 유전박막 물질자체와 계면에서의 물리적, 기계적인 특징의 측정이 상당히 중요해지고 있다. 이에 본 연구는 Nano-indenter의 통해 경도(Hardness)와 탄성계수(Elastic modulus) 등의 측정을 통하여 시료 표면의 나노영역에서의 기계적 특성을 연구하고자 하였다. $HfO_2$게이트 절연막은 rf magnetron sputter를 이용해 Si (silicon) (100)기판위에 박막형태로 증착하였고, 이후 furnace에서 질소분위기로 온도(400, 450, $500^{\circ}C$)를 달리하여 20분 열처리를 하였다. 또한 Weibull distribution을 이용해 박막의 characteristic value를 계산하였으며, 실험결과 열처리 온도가 $400^{\circ}C$에서 $500^{\circ}C$로 증가함에 따라 경도와 탄성계수는 7.4 GPa에서 10.65 GPa으로 120.25 GPa에서 137.95 GPa으로 각각 증가하였다. 이는 재료적 측면으로 재료의 구조적 우수성이 증가된 것으로 판단된다.

• The Journal of the Korea Contents Association
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• v.13 no.10
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• pp.427-433
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• 2013

The aim of this study was to evaluate the efficacy of bleached tooth with white toothpaste on the whitening effect, microhardness test. Forty-four human interior teeth were randomly assigned to two groups as follows: Group 1 was used general toothpaste as control, Group 2 exposed to white toothpaste at 3 times a day for 3 minutes. The total application time was 4 weeks. After each application, all tooth were washed with distilled water and immersed in artificial saliva. The color change and microhardness were measured using CIELab Color system and microhardness tester. The data were analyzed by student t-test, using SPSS 20.0 statistical computer program (SPSS Inc., USA). The overall color changes (${\Delta}E$) by white toothpaste have a capability of the whitening efficacy by factor of 2.3 times larger compared with general toothpaste. Moreover, the application of white toothpaste did not cause any microhardness reduction on enamel surface.