• Korean Journal of Materials Research
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• v.18 no.5
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• pp.241-246
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• 2008

Pure Mg and Mg-6wt.%Al alloy were coated by the plasma electrolytic oxidation with various coating times and the microstructural and mechanical characteristics of the coatings were investigated. The coatings on pure Mg and Mg-6wt.%Al alloy consisted of MgO and $Mg_2SiO_4$. The surface roughness and thickness of the coatings became larger as the coating time increased. The coatings on the Mg-6wt.%Al alloy were more uniform and thicker than those on pure Mg. The microhardness and friction coefficient of the coatings increased progressively as the coating time increased. In addition, the coatings on the Mg-6wt.%Al alloy compared to pure Mg showed improved microhardness and a better friction coefficient.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.2
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• pp.110-115
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• 2005

Plasma Transferred Arc Spray process was used to make modified surface for wear and corrosion resistant by using Co system powder type alloy. The modified surface was produced by changing only spray current and other process variables were constant. The current range was from 80 amp to 140 amp as inclosing 20 amp. It was appeared that the geometrical shape, microstructures and microhardness of the modified surface were affected by the different cooling rate of base metal. The modified surface that produced by 120 amp current exhibited the fine microstructure and the highest microhardness number impling good surface characteristics. It was also found that the spray current affected the width but not the height of the bead as increasing current.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.634-639
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• 1996

In oder to improve the wear resistance as well as oxidation resistance at high temperature a AISI H13 steel was treated by a duplex process of calorizing followed by plasma nitriding. The surface properties of the duplex-treated AISI H13 steel was characterized and compared with those treated by single surface process of calorizing and plasma nitriding, in terms of microstruture, microhardness, wear resistance at $500^{\circ}C$, and the oxidation behaviours at $700^{\circ}C$, Duplex process on H13 steel had created duplex layer of approximately $190\mu\textrm{m}$ on the surface, and surface microhardness was measured to be above 1450Hv(0.1Kgf). There was considerable improvement of the high temperature wear resistance at $500^{\circ}C$ in the duplex-treated steel when both wear volume and weight change due to oxidation were considered. In addition the duplex-treated steel showed an improved high temperature oxidation resistance than the plasma nitrided steel at $700^{\circ}C$.

• Journal of the Korean Vacuum Society
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• v.7 no.s1
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• pp.171-178
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• 1998

The microstructure and properties of plasma-sprayed coatings depend on a great number of spraying parameters, random factors, which lead to vibration in these spraying parameters, may in some degree influence the microstructure and properties of the coatings. Therefore, the property values appear certain distributions, and the description and comparison of the properties of plasma-sprayed coatings should be performed employing statistical analysis. In this paper, $Cr_3C_2$-Nicr coatings of different thickness were sprayed onto stainless steel using atmosphere plasma system and adopting three kinds of gun translation speeds. Then the microhardness measurements were performed on polished surface of the coatings. Forty readings were taken and statistically analyzed by calculating the characteristic values, estimating and comparing the means, and assessing whether they belonged to the Normal or Weibull Distribution. This study has found that statistical analysis could discriminate influence of spraying parameters and coating design on microhardness of the $Cr_3C_2$-Nicr coatings from random vibration, which showed that the microharness of the $Cr_3C_2$-Nicr coatings were related to gun translation speed coating thickness.

• Journal of the korean academy of Pediatric Dentistry
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• v.39 no.4
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• pp.383-388
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• 2012

The aim of this study was to compare the compressive strength and the surface microhardness of Beautifil flow (Shofu, Kyoto, Japan) with $Filtek^{TM}$ Z350, Z350XT (3M ESPE, USA). Fifteen specimens from each material were fabricated for testing. Compressive strength was measured by using a universal testing machine at a crosshead speed of 1 mm/min. Surface microhardness values were measured by using Vickers hardness tester under 4.9 N load and 10 seconds dwelling time. The compressive strength of Group 2 $Filtek^{TM}$ Z350XT shows the highest value as $218.7{\pm}18.4$ MPa and Group 1 $Filtek^{TM}$ Z350 was $205.5{\pm}27.1$ MPa. Group 3 Beautifil flow F00 was $176.5{\pm}30.3$ MPa, and Group 4 Beautifil flow F10 was $173.4{\pm}26.2$ MPa. The compressive strength of Group 2 is higher than Group 3 and 4 (p < 0.05). The surface microhardness of Group 2 $Filtek^{TM}$ Z350XT shows the highest value as $39.1{\pm}2.1$ and Group 4 Beautifil flow F10 was $27.9{\pm}1.8$. And Group 3 Beautifil flow F00 was $23.1{\pm}1.1$, Group 1 $Filtek^{TM}$ Z350 was $20.4{\pm}0.9$. There was a statistical significant difference in surface microhardness between all groups (p < 0.05). In conclusion, the compressive strength of giomer was below the level of flowable composite resin. However, the surface microhardness of giomer is comparable to that of flowable composite resin. Giomer would be the good alternative to composite resin, if there is improvement of the compressive strength of giomer.

• Journal of Convergence for Information Technology
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• v.9 no.7
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• pp.159-167
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• 2019

This study aimed to evaluate the effects of oral rinsing solution on the color stability, surface microhardness and surface roughness change of composite resin. In this in-vitro study, 80 disc-shaped specimens were fabricated of Filtek P60 and Filtek Z250(A2 shade). The samples of each group were randomly divided into eight subgroups (n=10). The baseline color values ($L^*$, $a^*$, $b^*$) of each specimen were measured according to CIE LAB system using a colorimeter. After baseline color measurements, the control samples were immersed in distilled water and the test groups were immersed colorless, green and purple mouthrinses three times a day for thirty minutes. This process was repeated for two weeks. Green and purple oral rinsing solutions displayed color, microhardness and roughness change of all composite resin after immersion in the mouthrinses. Therefore, prescription of oral rinsing solution for a minimum of two weeks is a common practice, which may cause discoloration of aesthetic composite restorations of patients.

• Restorative Dentistry and Endodontics
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• v.2 no.1
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• pp.38-49
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• 1976

Central and lateral incisors of 20, 40 and 60 age groups were bisected pararelly to long axis and middle portion of mesio-distal of teeth. And author measured the hardness of various areas in enamel and dentin with vickers hardness tester. Measured levels were divided into the labio-middle portion, middle portion of incisal edge and linguo-middle portion in enamel and dentin of all age groups. The results were as follows; 1) Total average hardness of enamel for 20, 40 and 60 age groups were respectively Hv. 366.5${\pm}$5.75, Hv. 372.9${\pm}$8.16 and Hv. 389.8${\pm}$10.27. 2) Total average hardness of dentin for 20, 40 and 60 age groups were respectively Hv. 51.0${\pm}$2.14, Hv. 54.0${\pm}$1.87 and Hv. 55.3${\pm}$2.23. 3) Total microhardness values in enamel and dentin of 60 age group was highered than 20 and 40 age groups. 4) The hardness values of enamel and dentin in all age groups were detected lower value on the middle portion of incisal edge than the labio-middle portion and linguo-middle portion. 5) Microhardness values of enamel was highered gradually from the dentinoenamel junction to the outer surface and it lowered at the outermost surface in all age groups. The microhardness values of dentin were the highest values at 600${\mu}$ from dentino-enamel junction and the lowest values at near the pulp chamber in all age groups.

• Restorative Dentistry and Endodontics
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• v.28 no.4
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• pp.354-359
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• 2003

This study evaluated the effectiveness of the light emitting diode(LED) units for composite curing. To compare its effectiveness with conventional quartz tungsten halogen (QTH) light curing unit. the microhardness of 2mm composite. Z250, which had been light cured by the LEDs (Ultralume LED2, FreeLight, Developing product Dl) or QTH (XL 3000) were compared on the upper and lower surface. One way ANOVA with Tukey and Paired t-test was used at 95% levels of confidence. In addition. the amount of linear polymerization shrinkage was compared between composites which were light cured by QTH or LEDs using a custom-made linometer in 10s and 60s of light curing, and the amount of linear polymerization shrinkage was compared by one way ANOVA with Tukey. The amount of polymerization shrinkage at 10s was XL3000 > Ultralume 2. 40. 60 > FreeLight, D1 (P<0.05) The amount of polymerization shrinkage at 60s was XL3000 > Ultralume 2, 60> Ultralume 2.40 > FreeLight, D1 (P<0.05) The microhardness on the upper and lower surface was as follows ; (equation omitted) It was concluded that the LEDs produced lower polymerization shrinkage in 10s and 60s compared with QTH unit. In addition. the microhardness of samples which had been cured with LEDs was lower on the lower surfaces than the upper surfaces whereas there was no difference in QTH cured samples.

• The Journal of the Korea Contents Association
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• v.13 no.4
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• pp.312-319
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• 2013

The purpose of this study was to evaluate the efficacy of gargle and toothpaste containing low concentration with sodium fluoride on the remineralization through the surface microhardness and mineral content in enamel. After 4 weeks-application, the enamel surface was measured using microhardness tester and the calcium (Ca) and phosphorous (P) concentration of mineral content by electron probe microanalyzer (EPMA) analysis. By combining fluoridated gargle with toothpaste, a remineralized enamel resulted in significantly significant differences among the four groups (p<0.05). The Ca change treated with 0.23% fluoridated toothpaste and 0.02% fluoridated gargle with 0.23% toothpaste demonstrated the highest among the other groups. In conclusion. the fluoridated gargle with toothpaste by low concentration showed a significantly greatest synergistic effect on remineralization of the enamel than the other groups.

• Journal of Korean society of Dental Hygiene
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• v.19 no.1
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• pp.151-159
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• 2019

Objective: This study aimed to investigate the relation between rinsing time and the change in enamel surface after fluoride application on the enamel surface. Methods: We recruited two sample groups with different mouth rinsing times. While one group rinsed the teeth immediately after applying acidulated phosphate fluoride (APF) gel, the other group rinsed the teeth 30 minutes after APF gel application. In each group, we performed the following four-step experiment: (i) apply APF gel on the teeth, (ii) rinse the teeth, (iii) immerse the teeth in orange juice, and (iv) measure enamel surface microhardness and scan enamel surfaces. Results: The group that rinsed 30 minutes after treatment exhibited greater microhardness than the group that rinsed immediately after fluoride treatment. The former also showed smooth and regular crystallization, whereas the latter showed rough and damaged crystallization and irregular surfaces. Conclusions: Based on these observations, we conclude that delaying the rinsing time improves the dental caries preventive effect of fluoride.