• Journal of Welding and Joining
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• v.13 no.4
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• pp.55-64
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• 1995

A study was made to examine the effects of postweld heat treatment(PWHT) on the toughness and microstructures in the weld heat affected zone(HAZ) of Cu-bearing HSLA-100 steel. The Gleeble thermal/mechanical simulator was used to simulate the weld HAZ. The details between toughness and PWHT of HAZ were studied by impact test, optical microscopy(O.M.), scanning electron microscopy (SEM), transmission electron microscopy(TEM) and differential scanning calorimetry(DSC). The decrease of HAZ toughness in single thermal cycle comparing to base plate is ascribed to the coarsed-grain formed by heating to 1350.deg.C. The increase of HAZ toughness in double thermal cycle comparine to single thermal cycle is due to the fine ferrite(.alpha.) grain transformed from austenite(.gamma.)formed by heating to .alpha./.gamma. two phase region. Cu precipitated during aging for increasing the strength of base metal is dissolved during single thermal cycle to 1350.deg.C and is precipitated little on cooling and heating during subsequent weld thermal cycle. It precipitates by introducing PWHT. Thus, the decrease of toughness in triple thermal cycle of $T_{p1}$ = 1350.deg.C, $T_{p2}$ = 800.deg.C and $T_{p3}$ = 500.deg.C does not occur owing to the precipitation of Cu. The behaviors of Cu=precipitates in HAZ is similar to that in base plate. PWHT at 550.deg.C shows highest hardness and lowest toughness, whereas PWHT at 650.deg.C shows reasonable toughness, which improves the toughness of as-welded state.state.

• Journal of the korean academy of Pediatric Dentistry
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• v.40 no.4
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• pp.283-295
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• 2013

In this study, researchers tried to find the effect, if any, of aging treatment to the specimens with three different dentin bonding agents using MicroCT. One, 5th generation - [Adper$^{TM}$ Single bond Plus] and two 6th generation [AdheSE$^{(R)}$, Adper$^{TM}$ Prompt$^{TM}$ L-Pop$^{TM}$] dentin bonding agents were used in this study. Specimens were divided into 4 groups according to aging treatment method used. Group I : control group, Group II : thermocycled between $5^{\circ}C$ and $55^{\circ}C$ for 60 seconds dwell time 5,000 times, Group III : aged as Group II and artificially brushed 20,000 times, Group IV : aged as Group III and were stored in artificial saliva for 6 months. With Single bond Plus, Group II showed more microleakage than Group I (p < 0.05). Group II and Group III showed more microleakage than Group IV (p < 0.05). There were no statistically significant differences among the groups using AdheSE$^{(R)}$ and Prompt$^{TM}$ L-Pop$^{TM}$ (p > 0.05). Among Group I, AdheSE$^{(R)}$ showed more microleakage than Single bond Plus and Prompt$^{TM}$ L-Pop$^{TM}$ (p < 0.05). Among Group II, there were no statistically significant differences (p > 0.05). Among Group III, AdheSE$^{(R)}$ showed more microleakage than Single bond Plus and Prompt$^{TM}$ L-Pop$^{TM}$ (p < 0.05). Among Group IV, AdheSE$^{(R)}$ and Prompt$^{TM}$ L-Pop$^{TM}$ showed more microleakage than Single bond Plus (p < 0.05).

• Restorative Dentistry and Endodontics
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• v.32 no.4
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• pp.343-355
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• 2007

The objectives of this study was to evaluate the durability of 4 resin cements by means of microtensile bond strength test combined with thermocycling method and fractographic FE-SEM analysis. Experimental groups were prepared according to thermocycling (0, 1,000, 5,000) and the kind of resin cements, those were Variolink II, Multilink, Panavia F 2.0, Rely X Unicem. Flat dentin surfaces were created on mid-coronal dentin of extracted third molars. Then fresh dentin surface was grounded with 320-grit silicon carbide abrasive papers to create uniform smear layers. Indirect composite block (Tescera, Bisco Inc., Schaumburg, IL, USA) was fabricated ($12\;{\times}\;12\;{\times}\;6\;mm^3$). It's surface for bonding to tooth was grounded with silicon carbide abrasive papers from 180- to 600-grit serially, then sandblasted witk $20\;-\;50\;{\mu}m$ alumina oxide. According to each manufacturer's instruction, dentin surface was treated and indirect composite block was luted on it using each resin cement. For Rely X Unicem, dentin surface was not treated. The bonded tooth-resin block were stored in distilled water at $37^{\circ}C$ for 24 hours. After thermocycling, the bonded tooth-resin block was sectioned occluso-gingivally to 1.0 mm thick serial slabs using all Isomet slow-speed saw (Isomet, Buehler Ltd, Lake Bluff, IL, USA). These sectioned slabs were further sectioned to $1.0\;{\times}\;1.0\;mm^2$ composite-dentin beams. The specimens were tested with universal testing machine (EZ-Test, Shimadzu, Japan) at a crosshead speed of 1.0 mm/min with maximum load of 500 N. The data was analyzed using one-way ANOVA and Duncan's multiple comparison test at $p\;{\leq}\;0.05$ level. Within the limited results, we conclude as follows; 1. The bond strength of Variolink II was evaluated the highest among experimental groups and was significantly decreased after 1,000 thermocycling (p < 0.05). 2. The bond strength of Multilink was more affected by thermocycling than the other experimental groups and significantly decreased after 1,000 thermocycling (p < 0.05). 3. Panavia F 2.0 and Rely X Unicem showed the gradually decreased tendency of microtensile bond strength according to thermocycling but there was no significant difference (p > 0.05). 4. Adhesive based-resin cements showed lower bond strength with or without thermocycling than composite based-resin cements. 5. Variolink II & Multilink showed high bond strength and mixed failure, which was occurred with a thin layer of luting resin cement before thermocycling and gradually increased adhesive failure along the dentin surface after thermocycling. The bonding performance of resin cement can be affected by application procedure and chemical composition. Composite based-resin cement showed higher bond strength and durability than adhesive based-resin cement.

• Journal of Dental Rehabilitation and Applied Science
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• v.21 no.1
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• pp.15-23
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• 2005

The purpose of this study was to evaluate effect of aging and thermocycling on the tensile strength of restorative composite resins. Eight commercially available light-cured restorative composites (Heliomolar: HM, Palfique Estelite: PE, Spectrum: ST, UniFil-F: UF, Z100: ZH, Clearfil AP-X: CA, P60: PS, and Palfique Toughwell: PT) were selected as experimental materials. Rectangular-shaped tensile test specimens were fabricated in a teflon mold giving 5 mm in gauge length and 2 mm in thickness. All samples were stored in distilled water at $37^{\circ}C$ for 100 days. Every 10 days, specimens were thermocycled for 1,000 cycles with 15 seconds of dwelling time in each $5^{\circ}C$ and $55^{\circ}C$ water baths. Tensile testing was carried out at a crosshead speed of 0.5 mm/min and fracture surfaces were observed with a scanning electron microscope. The results obtained were summarized as follows; 1. The strength degradation of thermocycled group was severer than that of the aged group (P<0.01). 2. The tensile strength of the CA and ST groups were significantly higher than that of other groups after thermocycling treatment (P<0.05). 3. Fracture surfaces showed that the composite resin failure developed along the matrix and the filler/resin interface region.

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.3
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• pp.509-516
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• 2005

For the purpose of comparing the bond strengths of compomers to composite resin, composite Z250, and two polyacid modified composite resin, Dyract AP and F2000, were selected and investigated using universal testing machine for measuring the shear bond strengths. Additionally, the failure modes were examined by observing the fractured surfaces of each specimen. The following results were obtained. 1. The shear bond strength of Dyract AP to Z250 were higher than those of F2000, but there was no statistically significant difference between group 1 and group 3(p>0.05), and groups using fresh compomers showed higher bond strength than those using aged compomers(p<0.05). 2. After measuring the shear bond strength of each group, it was highest in group 5 and was lowest in group 9(p<0.05). 3. Although there was no statistically significant difference, groups treated with thermocycling showed lower bond strengths than those of non-thermocycling groups. 4. Overall compomer/composite resin failures were adhesive. Cohesive failures occurred mainly in groups using bonding agent. Based on these results, the application of a bonding agent on fresh polyacid-modified resin composite increases the bond strength between polyacid-modified resin composite and composite resin. Additionally, the surface of aged polyacid-modified resin composite has to be roughened mechanically and a bonding agent has to be used in combination with composite resin.

• Restorative Dentistry and Endodontics
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• v.34 no.1
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• pp.42-50
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• 2009

Deterioration of long-term dentin adhesion durability is thought to occur by hydrolytic degradation within hydrophilic domains of the adhesive and hybrid layers. This study investigated the hypothesis that priming the collagen network with an organic solvent displace water without collapse and thereby obtain good bond strength with an adhesive made of hydrophobic monomers and organic solvents. Three experimental adhesives were prepared by dissolving two hydrophobic monomers, bisphenol-A-glycidylmethacrylate (Bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA), into acetone, ethanol or methanol. After an etching and rinsing procedure, the adhesives were applied onto either wet dentin surfaces (wet bonding) or dentin surfaces primed with the same solvent (solvent-primed bonding). Microtensile bond strength (MTBS) was measured at 48 hrs, 1 month and after 10,000 times of thermocycles. The bonded interfaces were evaluated using a scanning electron microscope (SEM). Regardless of bonding protocols, well-developed hybrid layers were observed at the bonded interface in most specimens. The highest mean MTBS was observed in the adhesive containing ethanol at 48 hrs. With solvent-primed bonding, increased MTBS tendencies were seen with thermo cycling in the adhesives containing ethanol or methanol. However, in the case of wet bonding, no increase in MTBS was observed with aging.