• 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.

• The Journal of Advanced Prosthodontics
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• v.11 no.2
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• pp.128-137
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• 2019

PURPOSE. The aim of this study was to compare the effect of different finishing and polishing techniques on water absorption, water solubility, and microhardness of ceramic or glass-polymer based computer-aided design and computer-aided manufacturing (CAD/CAM) materials following thermocycling. MATERIALS AND METHODS. 150 disc-shaped specimens were prepared from three different hybrid materials and divided into five subgroups according to the applied surface polishing techniques. All specimens were subjected up to #4000 grit SiC paper grinding. No additional polishing has been done to the control group (Group I). Other polishing procedures were as follows: Group II: two-stage diamond impregnated polishing discs; Group III: yellow colored rubber based silicone discs; Group IV: diamond polishing paste; and Group V: Aluminum oxide polishing discs. Subsequently, 5000-cycles of thermocycling were applied. The analyses were conducted after 24 hours, 7 days, and 30 days of water immersion. Water absorption and water solubility results were analyzed by two-way ANOVA and Tukey post-hoc tests. Besides, microhardness data were compared by Kruskal-Wallis and MannWhitney U tests (P<.05). RESULTS. Surface polishing procedures had significant effects on water absorption and solubility and surface microhardness of resin ceramics (P<.05). Group IV exhibited the lowest water absorption and the highest microhardness values (P<.05). Immersion periods had no effect on the microhardness of hybrid ceramic materials (P>.05). CONCLUSION. Surface finishing and polishing procedures might negatively affect physical properties of hybrid ceramic materials. Nevertheless, immersion periods do not affect the microhardness of the materials. Final polishing by using diamond polishing paste can be recommended for all CAD/CAM materials.

• Journal of the Korean institute of surface engineering
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• v.39 no.1
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• pp.1-8
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• 2006

In this study, effect of sputtering after plasma nitriding and before PVD coating on the microstucture, microhardness, surface roughness and the adhesion strength of CrN thin films were investigated. Experimental results showed that this sputtering process not only removed surface compound layer which formed during a plasma nitriding process but also induced an alteration of the surface of plasma nitrided substrate in terms of microhardness distribution and surface roughness, which in turn affected the adhesion strength of PVD coatings. After sputtering, microhardness distribution showed general decrease and the surface roughness became increased slightly. The critical shear stress measured from the scratch test on the CrN coatings showed an approximately twice increase in the binding strength through the sputtering prior to the coating and this could be attributed to a complete removal of compound layer from the plasma nitrided surface and to an increase in the surface roughness after sputtering.

• Journal of the Korean institute of surface engineering
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• v.39 no.6
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• pp.268-275
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• 2006

In this study, effect of sputtering on the plasma-nitriding substrate and before PVD coating on the microstucture, microhardness, surface roughness and the adhesion strength of CrZrN thin films were investigated. Experimental results showed that this sputtering process not only removed surface compound layer which formed during a plasma nitriding process but also induced an alteration of the surface of plasma nitrided substrate in terms of microhardness distribution, surface roughness. This in turn affected the adhesion strength of PVD coatings. After sputtering, microhardness distribution showed general decrease and the surface roughness became increased slightly. The critical shear stress measured from the scratch test on the CrZrN coatings showed an approximately 1.4 times increase in the adhesion strength through the sputtering prior to the coating and this could be attributed to a complete removal of compound layer from the plasma nitrided surface and to an increase in the surface roughness after sputtering.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.4
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• pp.293-297
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• 1998

The influence of ion implantation on surface properties of polymers was studied. We investigated microhardness, friction, wear and wettablility of polyimide. Energies of 50, 200keV were used with doses range from $1{\times}10^{13} to 1{\times}10^{16} [ions/cm^2]$. The implanted ion species were B, N and Ar. The microhardness of polyimide was increased after implantation for doses of $1{\times}10^{15}\; [ions/cm^2]$. A reduction of the friction coefficient was in most case correlated with a reduction of wear. The contact angles of water for $B^+,N^+$ implanted polyimide decreased from $76^{\circ}C$ to zero, as the fluencies increased at energies of 50 and 200 KeV. However, the contact angle of Ar ion implanted polyimide did not change under ambient room conditions even if the time elapsed. SEM measurement was performed to characterize the modified surface layer.

• Restorative Dentistry and Endodontics
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• v.41 no.1
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• pp.12-21
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• 2016

Objectives: To evaluate the effects of three acids on the microhardness of set mineral trioxide aggregate (MTA) and root dentin, and cytotoxicity on murine macrophage. Materials and Methods: OrthoMTA (BioMTA) was mixed and packed into the human root dentin blocks of 1.5 mm diameter and 5 mm height. Four groups, each of ten roots, were exposed to 10% citric acid (CA), 5% glycolic acid (GA), 17% ethylenediaminetetraacetic acid (EDTA), and saline for five minutes after setting of the OrthoMTA. Vickers surface microhardness of set MTA and dentin was measured before and after exposure to solutions, and compared between groups using one-way ANOVA with Tukey test. The microhardness value of each group was analyzed using student t test. Acid-treated OrthoMTA and dentin was examined by scanning electron microscope (SEM). Cell viability of tested solutions was assessed using WST-8 assay and murine macrophage. Results: Three test solutions reduced microhardness of dentin. 17% EDTA demonstrated severe dentinal erosion, significantly reduced the dentinal microhardness compared to 10% CA (p = 0.034) or 5% GA (p = 0.006). 10% CA or 5% GA significantly reduced the surface microhardness of set MTA compared to 17% EDTA and saline (p < 0.001). Acid-treated OrthoMTA demonstrated microporous structure with destruction of globular crystal. EDTA exhibited significantly more cellular toxicity than the other acidic solutions at diluted concentrations (0.2, 0.5, 1.0%). Conclusions: Tested acidic solutions reduced microhardness of root dentin. Five minute's application of 10% CA and 5% GA significantly reduced the microhardness of set OrthoMTA with lower cellular cytotoxicity compared to 17% EDTA.

• Restorative Dentistry and Endodontics
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• v.45 no.1
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• pp.12.1-12.8
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• 2020

Objectives: The aim of this in vitro study was to evaluate the microhardness and surface roughness of composite resins before and after tooth bleaching procedures. Materials and Methods: Sixty specimens were prepared of each composite resin (Filtek Supreme XT and Opallis), and BisCover LV surface sealant was applied to half of the specimens. Thirty enamel samples were obtained from the buccal and lingual surfaces of human molars for use as the control group. The surface roughness and microhardness were measured before and after bleaching procedures with 35% hydrogen peroxide or 16% carbamide (n = 10). Data were analyzed using 1-way analysis of variance and the Fisher test (α = 0.05). Results: Neither hydrogen peroxide nor carbamide peroxide treatment significantly altered the hardness of the composite resins, regardless of surface sealant application; however, both treatments significantly decreased the hardness of the tooth samples (p < 0.05). The bleaching did not cause any change in surface roughness, with the exception of the unsealed Opallis composite resin and dental enamel, both of which displayed an increase in surface roughness after bleaching with carbamide peroxide (p < 0.05). Conclusions: The microhardness and surface roughness of enamel and Opallis composite resin were influenced by bleaching procedures.

• Journal of the Korean institute of surface engineering
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• v.43 no.5
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• pp.224-229
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• 2010

$Ni-Si_3N_4$ nano-composite coatings were prepared by pulse current (PC) electrodeposition and direct current (DC) electrodeposition techniques. The micro-structure of the coatings was characterized by scanning electron microscopy (SEM), vickers microhardness, X-Ray Diffraction (XRD) and wear-friction tests. The results showed that the micro-structure and wear performance of the coatings were affected by the electrodeposition techniques. Pulse current electrodeposited $Ni-Si_3N_4$ composite coatings exhibited higher microhardness, smooth surface, and better wear resistance properties as compared to coatings prepared under DC condition. The $Ni-Si_3N_4$ composite coatings prepared at 50 Hz pulse frequency with 10% duty cycles has shown higher codeposition of nano-particles. Consequently, increased microhardness and less plastic deformations occurred in coatings during sliding wear test. The XRD patterns revealed that the increased pulse frequencies changed the preferred (100) nickel crystallite orientations into mixed (111) and (100) orientations.

• Journal of the Korean institute of surface engineering
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• v.43 no.4
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• pp.165-169
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• 2010

$Ni-Al_2O_3$ nanocomposite coatings were fabricated by conventional electrodeposition technique using nickel sulfamate bath. Effect of plating parameters on electrodeposition of $Ni-Al_2O_3$ nanocomposite were studied. The properties of the nano composite were investigated by using SEM, XRD, and Vicker's microhardness test. The results demonstrated that $Al_2O_3$ incorporation in the composite coatings was found to be increased by increasing stir rate and $Al_2O_3$ content in plating bath. Microhardness of the composite coatings was also increased with increasing content of the nano particles in the plating bath. The surface morphologies of the nanocomposite coatings were found to be varied with varying pH, current densities as well as alumina content in the plating bath.

• Journal of the Korean institute of surface engineering
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• v.29 no.3
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• pp.149-156
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• 1996

Conducting diamond-like carbon films are synthesized using Triode Magnetron Sputtering-Plasma Enhanced Chemical Vapor Deposition(TMS-PECVD), and are examined by four point probe, microhardeness tester, and scanning electron miscroscopy(SEM). As the target bias and Ar/CH$_4$, ratio increase, the electrical resitivity and microhardness of the films are found to decrease, and also, their surface morphologies tend to be rough. While the resistivities of the films are shown to increase in proportion to the increase of the substrate bias, the microhardness of the films is shown to be maximun value(1600kg/$\textrm{mm}^2$) at a certain substrate bias(-70V). We can obtain the conducting diamond-like carbon films with the microhardness of 1600(kg/$\textrm{mm}^2$) and electrical resitivity of 16($\Omega$cm) at the process condition such as target bias -400V, substrate bias -70V, and Ar/$CH_4$ ratio 20.