• Restorative Dentistry and Endodontics
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• v.27 no.1
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• pp.87-94
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• 2002

The purpose of this study was to evaluate the color changes of composite resin polymerized with three type of light curing units. Composite resin (Z100, shade A2) were applied in a cylindrical metal mold(2 mm thick, 7 mm diameter). Twenty specimens according to light curing units were made. Group 1 : the specimens were polymerized with Apollo 95E for 3seconds(1370 mW/$\textrm{cm}^2$). Group 2 : the specimens were polymerized with XL 3000 for 40seconds (480 mW/$\textrm{cm}^2$). Group 3 : the specimens were polymerized with Spectrum 800 for 10 seconds(250 mW/$\textrm{cm}^2$) and 30 seconds(700 mW/$\textrm{cm}^2$). The microhardness values(VHN) of upper and lower surfaces specimens after light polymerization were measured for the degree of polymerization. All specimens were stored in distilled water at 6$0^{\circ}C$ for 30 days. The color characteristics(L$^*$, a$^*$, b$^*$) of the specimens before and after immersion were measured by spectrophotometer and the total color difference ($\Delta$E$^*$) was computed. The results obtained were as follows : 1. The microhardness values of Group I showed significantly lower than those of Group II and III (p<0.05). 2. In all groups the $\Delta$E$^*$ values presented below 2.0. 3 Group I showed the highest $\Delta$E$^*$ values followed order from highest to lowest by Group II and III (p<0.05).

• Journal of Biosystems Engineering
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• v.40 no.3
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• pp.212-223
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• 2015

Purpose: Physical properties of Detarium microcarpum seeds were investigated as a function of moisture content to explore the possibility of developing bulk handling and processing equipment. Methods: Seed size, surface area, and 1,000-seed weight were determined by measuring the three principal axes, measuring area on a graph paper, and counting and weighing seeds. Particle and bulk densities were determined using liquid displacement and weight in a measuring cylinder, respectively. Porosity was computed from particle and bulk densities. Roundness and sphericity were measured using shadowgraphs. Angle of repose and static and kinetic coefficients of friction were determined using the vertical cylindrical pipe method, an inclined plane, and a kinetic coefficient of friction apparatus. Results: In the moisture range of 8.2%-28.5% (db), the major, intermediate, and the minor axes increased from 2.95 to 3.21 cm, 1.85 to 2.61 cm, and 0.40 to 1.21 cm, respectively. Surface area, 1,000-seed weight, particle density, porosity, and angle of repose increased from 354.62 to $433.19cm^2$, 3.184 to 3.737 kg, 1060 to $1316kg/m^3$, and 30.0% to 53.1%, respectively, whereas bulk density decreased from 647.6 to $617.2kg/m^3$. Angle of repose increased from $13.9^{\circ}$ to $28.4^{\circ}$. Static and kinetic coefficients of friction varied between 0.096 and 0.638 on different structural surfaces. Conclusions: Arithmetic mean, geometric mean, and equivalent sphere effective diameters determined at the same moisture level were significantly different from each other, with the arithmetic mean diameter being greatest. Surface area, 1,000-seed weight, particle density, porosity, and angle of repose all increased linearly with moisture content. Bulk density decreased linearly with moisture content. The coefficients of friction had linear relationships with moisture content. The highest values of static and kinetic coefficients of friction were observed on galvanized steel and hessian fabric, respectively, whereas the lowest values were observed on fiberglass.

• Journal of the korean academy of Pediatric Dentistry
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• v.23 no.2
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• pp.450-460
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• 1996

The purpose of this study was to compare shear bond strength of composite resin using several dentin bonding agents and light cured glass ionomer cement(Fuji II LC). 40 Bovine primary anterior teeth were used for this experiment. Labial surface of teeth were flattened. It were divided into four groups. Each group was composed of 10 teeth. The material used for this experiment were Scotchbond Multipurpose-Z-100, Allbond 2-Aelitefil, Gluma-Pekalux, light cured glass ionomer cement(Fuji II LC). Each of the materials was applied to the exposed surfaces of 10 teeth by insertion into a cylindrical shaped matrix which is 3mm diameter and 3mm in height. The completed specimens were stored at $37^{\circ}C$ under 100% humidity for 24 hours : the shear bond strength of each material to dentin surface were measured with INSTRON universal testing machine. The results were as follows : 1. Shear bond strength to dentin surface increased in order of light cured glass ionomer cement(Fuji II LC), Gluma, Allbond 2, Scotchbond Multipurpose. 2. Between shear bond strength of light cured glass ionomer cement(Fuji II LC) and Allbond 2, there was statistical significace(p<0.05) 3. Between shear bond strength of light cured glass ionomer cement(Fuji II LC) and Scotchbond Multipurpose, between shear bond strength of Gluma and Scotchbond Multipurpose, there was statistical significance.(p<0.01) The shear bond strength of dentin bonding agents were higher than light cured glass ionomer cement. The reason is that materials and quality of dentin bonding agent were enhanced. Further investigation is necessary to improve shear bond strength of light cured glass ionomer cement.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.1
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• pp.91-109
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• 1991

The purpose of this study were to comfirm the effects of the thickness and kinds of porcelain, etchants, illumination time, elapsed time for the measurement, and chemical cure component to the bond strength of porcelain laminate and composite resin cement, and to compare the effects between the light cured resin and the dual cured resins. The etched porcelain surface, the sectioned surface crossing porcelain and resin after bonding, and the debonded surfaces were observed by the SEM. One product of laminate porcelain powder, one light cured resin and two dual cured resins were selected. Each resin cements are lightened through the thin porcelain disc which was cut from cylindrical porcelain specimen by the diamond saw, and by the light through the porcelain disc they were bonded. Changes of thickness and kinds of porcelain, etchants, illumination time, and the elapsed time for the measurement were considered as variables for the bond strength. And the bond strength of porcelain and dual cured resins under the conditions of autopolymerization or the removal of chemical cure component were measured and compared. Bond strength were measured by shear stress. The etched surface, the cross-sectioned surface, and the debonded surface of porcelain or resin were observed by SEM. On the summary of this study, the following conclusions can be stated; 1. Bond strength of light cured resin was decreased inversely by the thickened porcelain laminate and showed the lowest value to the masking dentin porcelain among 4 kinds of porcelain powder. 2. Bond strength of autopolymerization of dual cured resin without illumination in dark chamber were from 75% to 98% to the data of dual cured resin with illumination. 3. Bond strength of dual cured resin used without chemical cured components were same to them of light cured resin. 4. Cross-sectioned surface treated by silane did not show the gap between the porcelain and resin. 5. Illumination over 80 seconds did not make the significant increase of bond strength on all kinds of resin.

• Geomechanics and Engineering
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• v.12 no.2
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• pp.295-312
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• 2017

Cast in situ and grouted concrete helical piles with 150-200 mm diameter half cylindrical ribs have become an economical and effective choice in Shanghai, China for uplift piles in deep soft soils. Though this type of pile has been successful used in practice, the reinforcing mechanism and the contribution of the ribs to the total resistance is not clear, and there is no clear guideline for the design of such piles. To study the inclusion of ribs to the contribution of shear resistance, the shear behaviour between silty sand and concrete slabs with parallel ribs at different spacing and angles were tested in a large direct shear box ($600mm{\times}400mm{\times}200mm$). The front panels of the shear box are detachable to observe the soil deformation after the test. The tests were modelled with three-dimensional finite element method in ABAQUS. It was found that, passive zones can be developed ahead of the ribs to form undulated failure surfaces. The shear resistance and failure mode are affected by the ratio of rib spacing to rib diameter. Based on the shape and continuity of the failure zones at the interface, the failure modes at the interface can be classified as "punching", "local" or "general" shear failure respectively. With the inclusion of the ribs, the pull out resistance can increase up to 17%. The optimum rib spacing to rib diameter ratio was found to be around 7 based on the observed experimental results and the numerical modelling.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.3
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• pp.361-367
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• 2010

The barrel cam, which is a type of cylindrical cam, has been widely used as a part of index drive units for automatic manufacturing machines. The axis of rotation of the barrel cam is orthogonal to the axis of rotation of the follower. The index drive rotates or dwells depending on the cam profile, while the cam rotates with a constant velocity. Continuous sliding contact between the barrel cam and the follower surfaces causes wearing of the adhesive between them. This study shows that the contact force between two sliding bodies is responsible for the wear of the barrel cam in the paper-cup-forming machine. This contact force is calculated by using the multibody dynamics model of the paper-cup-forming machine. The analytical result is validated by comparing it to the actual wear spots on the real product.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.8
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• pp.15-27
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• 2008

In this paper, an EBG(Electromagnetic BandGap) resonator antenna with a stripline type FSS(Frequency Selective Surface) superstrate for PCS-band base station antennas is proposed. The characteristics of resonant frequency and -3dB bandwidth of a unit cell of a superstrate are first analyzed by varing several design parameters such as a strip width and a unit cell width in order to design an EBG resonator antenna satisfying the required antenna gain and bandwidth for PCS-band base station antennas. Among various unit cell shapes, strip dipole and stripline are considered and their characteristics are compared. It was found that a resonant length of the EBG resonator antenna becomes smaller when the stripline shape is used and the control of the bandwidth is also much easier. By using the unit cell simulation results, planar and cylindrical EBG resonator antennas at PCS-band are designed.

• Restorative Dentistry and Endodontics
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• v.40 no.2
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• pp.128-135
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• 2015

Objectives: This study evaluated the effects of the resin thickness on the microhardness and optical properties of bulk-fill resin composites. Materials and Methods: Four bulk-fill (Venus Bulk Fill, Heraeus Kulzer; SDR, Dentsply Caulk; Tetric N-Ceram Bulk Fill, Ivoclar vivadent; SonicFill, Kerr) and two regular resin composites (Charisma flow, Heraeus Kulzer; Tetric N-Ceram, Ivoclar vivadent) were used. Sixty acrylic cylindrical molds were prepared for each thickness (2, 3 and 4 mm). The molds were divided into six groups for resin composites. The microhardness was measured on the top and bottom surfaces, and the colors were measured using Commission Internationale d'Eclairage (CIE) $L^*a^*b^*$ system. Color differences according to the thickness and translucency parameters and the correlations between the microhardness and translucency parameter were analyzed. The microhardness and color differences were analyzed by ANOVA and Scheffe's post hoc test, and a student t-test, respectively. The level of significance was set to ${\alpha}=0.05$. Results: The microhardness decreased with increasing resin thickness. The bulk-fill resin composites showed a bottom/top hardness ratio of almost 80% or more in 4 mm thick specimens. The highest translucency parameter was observed in Venus Bulk Fill. All resin composites used in this study except for Venus Bulk Fill showed linear correlations between the microhardness and translucency parameter according to the thickness. Conclusions: Within the limitations of this study, the bulk-fill resin composites used in this study can be placed and cured properly in the 4 mm bulk.

• Journal of Technologic Dentistry
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• v.42 no.4
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• pp.326-333
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• 2020

Purpose: The purpose of this study was to evaluate the effects of various zirconia surface treatment methods on shear bond strength with resin cements. Methods: We prepared 120 cylindrical zirconia specimens (⌀10 mm×10 mm) using computer-aided design/computer-aided manufacturing (CAD/CAM). Each specimen was randomly subjected to one of four surface treatment conditions: (1) no treatment (control), (2) airborne-particle abrasion with 50 ㎛ of Al2O3 (A50), (3) airborne-particle abrasion with 125 ㎛ of Al2O3 (A125), and (4) ZrO2 slurry (ZA). Using a polytetrafluoroethylene mold (⌀6 mm×3 mm), we applied three resin cements (Panavia F 2.0, Super-Bond C&B, and Variolink N) to each specimen. The shear bond strength tests were performed in a universal testing machine. The surfaces of representative specimens of each group were evaluated under scanning electron microscope. We used one-way analysis of variance (ANOVA), two-way ANOVA, and post hoc Tukey honest significant difference test to analyze the data. Results: In the surface treatment method, the A50 group showed the highest bond strength, followed by A125, ZA, and control groups; however, no significant difference was observed between A50 and A125, A125 and ZA, and ZA and control (p>0.05). Among the resin cements, Super-Bond C&B showed the highest shear bond strength, followed by Panavia F 2.0 and Variolink N (p<0.05). Conclusion: Within the limitations of this study, application of airborne-particle abrasion and ZrO2 slurry improved the shear bond strength of resin cement on zirconia.

• Restorative Dentistry and Endodontics
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• v.47 no.1
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• pp.10.1-10.11
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• 2022

Objectives: This study aimed to investigate the color stability, solubility, and surface characteristics of 3 calcium silicate-based cements (CSCs) after immersion in different solutions. Materials and Methods: ProRoot white mineral trioxide aggregate (MTA), Biodentine, and Endosequence Root Repair Material (ERRM) were placed in cylindrical molds and stored at 37℃ for 24 hours. Each specimen was immersed in distilled water, 5% sodium hypochlorite (NaOCl), 2% chlorhexidine, or 0.1% octenidine hydrochloride (OCT) for 24 hours. Color changes were measured with a spectrophotometer. Solubility was determined using an analytical balance with 10^-5 g accuracy. The surface characteristics were analyzed using scanning electron microscopy and energy-dispersive spectroscopy. Data were analyzed using 2-way analysis of variance, the Tukey test, and the paired t-test. Results: MTA exhibited significant discoloration in contact with NaOCl (p < 0.05). White precipitation occurred on the surfaces of Biodentine and ERRM after contact with the solutions, and none of the materials presented dark brown discoloration. All materials showed significant solubility after immersion in the solutions (p < 0.05), irrespective of the solution type (p > 0.05). The surface topography and elemental composition of the samples showed different patterns of crystal formation and precipitation depending on the solution type. Conclusions: All materials presented some amount of solubility and showed crystal precipitation after contact with the solutions. Biodentine and ERRM are suitable alternatives to ProRoot MTA as they do not exhibit discoloration. The use of OCT can be considered safe for CSCs.