• Restorative Dentistry and Endodontics
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• v.39 no.1
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• pp.24-31
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• 2014

Objectives: The purpose of present study was to evaluate the internal adaptation of composite restorations using different adhesive systems. Materials and Methods: Typical class I cavities were prepared in 32 human third molars. The teeth were divided into the following four groups: 3-step etch-and-rinse, 2-step etch-and-rinse, 2-step self-etch and 1-step self-etch system were used. After the dentin adhesives were applied, composite resins were filled and light-cured in two layers. Then, silver nitrate solution was infiltrated, and all of the samples were scanned by micro-CT before and after thermo-mechanical load cycling. For each image, the length to which silver nitrate infiltrated, as a percentage of the whole pulpal floor length, was calculated (%SP). To evaluate the internal adaptation using conventional method, the samples were cut into 3 pieces by two sectioning at an interval of 1 mm in the middle of the cavity and they were dyed with Rhodamine-B. The cross sections of the specimens were examined by stereomicroscope. The lengths of the parts where actual leakage was shown were measured and calculated as a percentage of real leakage (%RP). The values for %SP and %RP were compared. Results: After thermo-mechanical loading, all specimens showed significantly increased %SP compared to before thermo-mechanical loading and 1-step self-etch system had the highest %SP (p < 0.05). There was a tendency for %SP and %RP to show similar microleakage percentage depending on its sectioning. Conclusions: After thermo-mechanical load cycling, there were differences in internal adaptation among the groups using different adhesive systems.

• Journal of dental hygiene science
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• v.21 no.3
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• pp.178-184
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• 2021

Background: As the importance of the esthetic function of teeth increases, the use of esthetic restoration materials and whitening treatment are increasing. The purpose of this study was to investigate the color change of esthetic restoration materials upon using staining and whitening toothpaste. Methods: Light curing (LC) packable composite resin, LC flowable resin, LC glass ionomer (GI), and self-curing GI specimens were colored in coffee or curry for three hours a day for seven days. After that, regular toothpaste, whitening toothpaste containing hydrogen peroxide, and whitening toothpaste containing activated charcoal were applied for three minutes three times a day for two weeks. Luminosity (L), chromaticity a (a), and chromaticity b (b) were measured using a spectrophotometer once a week. Results: In the coffee-colored group, the change in L^2*a^2*b² (E²) with time was significant (p=0.004), there was no difference for different toothpaste types (p=0.646), and there was significant difference (p<0.001) for different esthetic restorative materials. The change of E² in the curry-colored group was significant only for different esthetic restorative materials (p<0.001). In the coffee-colored group, the L, a, and b values of the light-curing GI showed greater change than other materials after staining and one week after whitening, turning dark, red, and yellow. In the curry-colored group, L did not differ for different materials and times, and a and b showed the greatest difference in light-curing GI after staining and one and two weeks after whitening. Conclusion: The use of whitening toothpaste for two weeks was not different from the use of general toothpaste in the removal of staining or whitening. Since light-curing GI is the most vulnerable to coloration, it is recommended that coloring by food chromogen should be explained in advance, before using light-curing GI for teeth restoration.

• Journal of dental hygiene science
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• v.19 no.1
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• pp.39-47
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• 2019

Background: Light-emitting diodes curing unit (LCU), which emit blue light, is used for polymerization of composite resins in many dentistry. Although the use of LCU for light-cured composite resin polymerization is considered safe, it is still controversial whether it can directly or indirectly have harmful biological influences on oral tissues. The aim of this study was to elucidate the biological effects of LCU in wavelengths ranging from 440 to 490 nm, on the cell viability and secretion of inflammatory cytokines in MDPC-23 odontoblastic cells and inflammatory-induced MDPC-23 cells by lipopolysaccharide (LPS). Methods: The MTT assay and observation using microscope were performed on MDPC-23 cells to investigate the cell viability and cytotoxic effects on LCU irradiation. Results: MDPC-23 cells and LPS stimulated MDPC-23 cells were found to have no effects on cell viability and cell morphology in the LCU irradiation. Nitric oxide (NO) and prostaglandin $E_2$ which are the pro-inflammatory mediators, and interleukin-$1{\beta}$ and tumor necrosis factor-${\alpha}$ (TNF-${\alpha}$) which are the proinflammatory cytokines were significantly increased in MCPD-23 cells after LCU irradiation as time increased in comparison with the control. LCU irradiation has the potential to induce inflammation or biological damages in normal dental tissues, including MDPC-23 cells. Conclusion: Therefore, it is necessary to limit the use of LCU except for the appropriate dose and irradiation time. In addition, LCU irradiation of inflammatory-induced MDPC-23 cells by LPS was reduced the secretion of NO compared to the LPS alone treatment group and was significantly reduced the secretion of TNF-${\alpha}$ in all the time groups. Therefore, LCU application in LPS stimulated MDPC-23 odontoblastic cells has a photodynamic therapy like effect as well as inflammation relief.

• Restorative Dentistry and Endodontics
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• v.44 no.1
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• pp.1.1-1.12
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• 2019

Objectives: The aim of this in vitro study was to test the effect of 2 finishing-polishing sequences (QB, combining a 12/15-fluted finishing bur and an EVO-Light polisher; QWB, adding a 30-fluted polishing bur after the 12/15-fluted finishing bur used in the QB sequence) on 5 nanotech-based resin composites (Filtek Z500, Ceram X Mono, Ceram X Duo, Tetric Evoceram, and Tetric Evoceram Bulk Fill) by comparing their final surface roughness and hardness values to those of a Mylar strip control group (MS). Materials and Methods: Twelve specimens of each nanocomposite were prepared in Teflon moulds. The surface of each resin composite was finished with QB (5 samples), QWB (5 samples), or MS (2 samples), and then evaluated (60 samples). Roughness was analysed with an optical profilometer, microhardness was tested with a Vickers indenter, and the surfaces were examined by optical and scanning electron microscopy. Data were analysed using the Kruskal-Wallis test (p < 0.05) followed by the Dunn test. Results: For the hardness and roughness of nanocomposite resin, the QWB sequence was significantly more effective than QB (p < 0.05). The Filtek Z500 showed significantly harder surfaces regardless of the finishing-polishing sequence (p < 0.05). Conclusions: QWB yielded the best values of surface roughness and hardness. The hardness and roughness of the 5 nanocomposites presented less significant differences when QWB was used.

• Composites Research
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• v.35 no.4
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• pp.255-260
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• 2022

Lightweight hydrant tanks increase the amount of water that can be carried by fire trucks, resulting in longer water spray times during the initial firefighting process, which can minimize human and property damages. In this study, the applicability of carbon-fiber-reinforced polymer (CFRP) composites as a material for lightweight hydrant tanks was investigated. In particular, the resin for manufacturing CFRP hydrant tanks must meet various requirements, such as excellent mechanical properties, formability, and dimensional stability. In order to identify a resin that satisfies these conditions, five commercially available resins, including epoxy(KFR-120V), unsaturated polyesters(G-650, HG-3689BT, LSP8020), vinyl ester(KRF-1031) were selected as candidates, and their characteristics were analyzed to investigate the suitability for manufacturing a CFRP hydrant tank. Based on the analyses, KRF-1031 exhibited the most suitable properties for hydrant tanks. Particularly, CFRP with KRF-1031 exhibited successful results for thermal stability and elution tests.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.1
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• pp.62-70
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• 2009

The objective of this study was to measure the leaching of filler (Si, Ba) from nanofiller-contained composites (Palfique Estelite $sigma^{{R}}$ (Tokuyama Dental Corp., Tokyo, Japan), $Z-350^{{R}}$ (3M ESPE, USA), Ceram X duo $E3^{{R}}$, $D3^{{R}}$ (Dentsply, Konstanz, Germany)) under different conditions. The samples used for the study of leachable components were made by insertion of the material into a circular mold, 10 mm in diameter and 3.0 mm high. Each specimen was placed in a disposable polystyrene vial containing 5 mL of distilled water, artificial saliva or 0.1N NaOH and kept in an oven at $37^{\circ}C$. ; water and artificial saliva - 150 days, 0.1N NaOH - 15days. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to determine the amount of Si and Ba in the test solutions. 1. Filler leaching was significantly great in 0.1N NaOH among all samples(p<.0.001). 2. When samples were stored in the distilled water, Estelite showed the lowest amount of Si leaching. When samples were stored in the artificial saliva, Z-350 showed the lowest amount of Si leaching. 3. There were significant differences in filler leaching between 3 storage medias and composite resins(p<.0.001). 4. Si and Ba leaching occurred in greater proportion when samples were stored in the artificial saliva than distilled water. 5. There were significant interactions in monthly filler leaching between leaching in artificial saliva and in distilled water, as well as the interaction between storage medium and filler(p<.0001). These results indicate that a continuous filler leaching of nanofiller-contained composite resins was in storing aqueous solutions under over time.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.1
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• pp.43-52
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• 2006

Topical fluoride application for children is a widely peformed procedure in the field of pediatric dentistry to prevent dental caries. However, it is recently recognized as having some unwanted effects on several esthetic restorative materials as it roughens the surface of the restorative materials. The aim of this study was to evaluate the surface changes in composite resins to topical fluoride. Composite resins(Z $250^{(R)}$, Ultraseal $XT^{(R)}$ Filtek $flow^{(R)}$ $Revolution^{(R)}$, $Denfil^{(R)}$) in topical fluoride agents were immersed and their surface roughness, weight loss and SEM were evaluated. The results were as follows : 1. The 4 minutes-immersion groups showed more roughened surface than 1 minute-immersion groups and the control groups showed the smoothest surface among all the materials, and there was statistically significant difference except the revolution between the groups. 2. There was no significant difference between the 1 minute-immersion groups and 4 minutes-immersion groups in weight loss. 3. The experimental group treated with topical fluoride gel showed the generally mere roughened surface than control group in the SEM findings.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.4
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• pp.685-695
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• 2004

The aim of this study was to evaluate the resistance to degradation and to compare the wear resistance characteristics of four composite resins in an alkaline solution. The resistance to degradation was evaluated on the basis of mass loss(%), degradation depth(${\mu}m$), Si loss(ppm) and wear depth. The brands studied were Heliomolar flow, Filtek supreme, Point4, Tetric flow. The results were as follows: 1. The sequence of the mass loss was in descending order by Heliomolar flow, Filtek supreme, Point4, Tetric flow. There was significant differences among the materials except Heliomolar flow and Filtek supreme. 2. The sequence of the degree of degradation layer depth was in descending order by Filtek supreme, Heliomolar flow, Tetric flow, Point4. There were significant differences among the materials except Heliomolar flow and Tetric flow. 3. The sequence of Si loss was in descending order by Filtek supreme, Heliomolar flow, Point4, Tetric flow. There were significant differences among the materials except Point 4 and Tetric flow. 4. The sequence of maximum wear depth was in descending order by Heliomolar flow, Point4, Fillet supreme, Tetric flow and there was increasing wear depth on soaking in 0.1N NaOH solution. 5. When observed with SEM, destruction of bonding between matrix and filler was observed and when observed with CLSM, the depth of degradation layer of specimen surface was observed. There results indicate that wear and hydrolytic degradation could be considered to be evaluation factors of composite resins.

• Restorative Dentistry and Endodontics
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• v.34 no.5
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• pp.450-459
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• 2009

The aim of this study was to measure the initial dynamic modulus changes of light cured composites using a custom made rheometer. The custom made rheometer consisted of 3 parts: (1) a measurement unit of parallel plates made of glass rods, (2) an oscillating shear strain generator with a DC motor and a crank mechanism, (3) a stress measurement device using an electromagnetic torque sensor. This instrument could measure a maximum torque of 2Ncm, and the switch of the light-curing unit was synchronized with the rheometer. Six commercial composite resins [Z-100 (Z1), Z-250 (Z2), Z-350 (Z3), DenFil (DF), Tetric Ceram (TC), and Clearfil AP-X (CF)] were investigated. A dynamic oscillating shear test was undertaken with the rheometer. A certain volume ($14.2\;mm^3$) of composite was loaded between the parallel plates, which were made of glass rods (3 mm in diameter). An oscillating shear strain with a frequency of 6 Hz and amplitude of 0.00579 rad was applied to the specimen and the resultant stress was measured. Data acquisition started simultaneously with light curing, and the changes in visco-elasticity of composites were recorded for 10 seconds. The measurements were repeated 5 times for each composite at $25{\pm}0.5^{\circ}C$. Complex shear modulus G*, storage shear modulus G', loss shear modulus G" were calculated from the measured strain-stress curves. Time to reach the complex modulus G* of 10 MPa was determined. The G* and time to reach the G* of 10 MPa of composites were analyzed with One-way ANOVA and Tukey's test ($\alpha$ = 0.05). The results were as follows. 1. The custom made rheometer in this study reliably measured the initial visco-elastic modulus changes of composites during 10 seconds of light curing. 2. In all composites, the development of complex shear modulus G* had a latent period for $1{\sim}2$ seconds immediately after the start of light curing, and then increased rapidly during 10 seconds. 3. In all composites, the storage shear modulus G" increased steeper than the loss shear modulus G" during 10 seconds of light curing. 4. The complex shear modulus of Z1 was the highest, followed by CF, Z2, Z3, TC and DF the lowest. 5. Z1 was the fastest and DF was the slowest in the time to reach the complex shear modulus of 10 MPa.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.10a
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• pp.160-166
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• 1994

In general, the problems of strengthening and repairing of deteriorated or damaged reinforced concrete members are usually worked out in situ by externally bounding steel plates using epoxy resins, which has been recognized to be one of effective and convenient methods. But the disadvantages of strengthening/repairing concrete members with externally bonded steel plates include ; (a) deterioration of the bond at the steel-concrete interface caused by the corrosion of steel ; (b) difficulty in manipulating the plate at the construction site ; (c) improper formation of joints, due to the limited delivery lengths of the steel plates ; and etc. Therefore these difficulties eventually have led to the concept of replacing the steel plates by fiber-reinforced composite sheets which are characterized by their light weight, extremely high stiffness, excellent fatigue properties, and outstanding corrosion resistance. In the paper, for the reliability assessment of reinforced concrete beams externally strengthened by carbon fiber plastic(CFRP) laminates, an attempt is made to suggest a limit state model based on the strain compatibility method and the concept of fracture mechanics. And the reliability of the proposed models is evaluated by using the AFOSM method. The load carrying capacity of the deteriorated and/or damaged RC beams is considerably increased. Thus, it may be stated that the post-strengthening of concrete beams with externally bonded CFRP materials may be one of very effective way of increasing the load carrying capacity and stiffeness characteristics of existing structures.