Comparison of microleakage of a multi-mode adhesive system with contemporary adhesives in class II resin restorations

Aim: The aim was to compare the microleakage of resin composite bonded with different adhesive systems in class-II cavities at enamel or dentine margins. Material and methods: 60 extracted human molar teeth received slot cavity preparations on mesial and distal surfaces (mesial cervical margin was prepared in enamel and distal in dentine). They were randomly divided into five groups (n?=?12) according to the adhesive system: Group-A: Silorane Bond (S), Group-B: Adper Single Bond 2 (SB), Group-C: Clearfil SE Bond (CSE), Group-D: Single Bond Universal (USel) (selective etch-and-rinse), Group-E: Single Bond Universal (USE) (all-in-one). The preparations were restored using the same resin composite (Filtek Ultimate) except Group A which was restored by Silorane composite. The teeth were thermocycled, immersed in dye, sectioned, and dye penetration was evaluated quantitatively using image analysis. The data were analyzed using the two-way analysis of variance and Bonferroni test. Results: In all groups, there was no statistically significant difference between enamel margins at occlusal and gingival sites (p?>?0.05). The statistical difference between Group-A (S) and Group-B (SB) was significant at all margins. Group-B (SB) presented the greatest microleakage amounts at all margins and the highest scores were obtained in the dentine. Likewise, SB demonstrated statistically significant differences between dentine and enamel margins (occlusal and gingival)(p?<?0.05). Conclusion: All adhesive systems showed similar microleakage values between enamel margins in occlusal and gingival regions. However, when the gingival margin is located in the dentine, etch&rinse adhesive systems may not be a choice in terms of microleakage prevention.     

Novel Amide-Based Cationic Surfactants as Efficient Corrosion Inhibitors for Carbon Steel in HCl and H2SO4 media

A variety of surface active compounds were synthesized by the quaternization of some straight chain amide derivatives with triethylamine or pyridine. Their structure FT-IR and ¹H-NMR spectra were recorded. In addition their physical properties and corrosion prevention efficiencies were investigated. All compounds were tested with steel coupons in acidic media by the gravimetric method. As acidic media 1.5 M HCl and 1.5 M H₂SO₄ were used and the corrosion inhibition tests fulfilled at room temperature for 24 h. Almost all prepared cationic surfactants showed efficient inhibition around their critical micelle concentrations. The effects of HCl concentration on corrosion inhibition of some synthesized compounds were also investigated. The corrosion tests were supported by contact angle measurements.     

Fabrication of Si3N4 preforms from Si3N4 produced via CRN technique

Ceramic preforms with randomly distributed particles as reticulated porous structure which are generally used for metal infiltration as reinforcement, membranes, catalyst supports etc. Preforms are characterized by open porosity making possible their infiltration by liquid metal alloys. In this work, quartz powders using carbon black as a reducing agent were used for alpha Si₃N₄ powders synthesis through a carbothermal reduction and nitridation (CRN) process. The CRN process was carried out under nitrogen flow at 1,450 °C for 4 h. At high temperatures, carbon as reducing agent reacts with the oxygen of SiO₂, and the resulting metallic silicon compounds with nitrogen gas to obtain silicon nitride powder. The reacted powders were used to obtain reticulated ceramic by replica method. The powders containing various bentonite ratios were mixed in water to prepare slurry. The slurry was infiltrated into a polyurethane sponge. A high porous ceramic foam (preform) structure was achieved after burn out of the sponge. All ceramic preforms were sintered to increase stiffness (in the temperature range 900–1,350 °C). The sintered ceramic foams were subjected to compressive tests. The scanning electron microscopy was used to examine the reticulated ceramic foam structure, and X-ray diffraction analysis was performed to determine phases.     

Catalytic effect of potassium carbonate on carbothermic production of hexagonal boron nitride

Effect of potassium carbonate addition on the carbothermic formation of hexagonal boron nitride (hBN) was investigated by keeping the K₂CO₃ added B₂O₃+C mixtures in nitrogen atmosphere at 1400 °C for 40–160 min. K₂CO₃ amount was varied in the range of 10–60 wt% of the B₂O₃+C mixture. Products were subjected to XRD and quantitative analyses, SEM and TEM observations, and particle size measurement. Amount of hBN increased considerably with K₂CO₃ addition; also particle size and crystallinity improved. Catalytic role of K₂CO₃ was suggested as forming a potassium borate melt in which hBN particles form, in addition to carbothermic formation reaction. Effect of K₂CO₃ on increasing the hBN amount decreased when it was used over 40%. This was attributed to the rapid evaporation of the formed potassium borate liquid.     

The effect of preparation temperature on the swelling behavior of poly (N-isopropylacrylamide) gels

Summary The role of the preparation temperature of poly(N-isopropylacrylamide) (PNIPA) gels on their swelling behavior in water and in aqueous solutions of sodium dodecylbenzenesulfonate was investigated. PNIPA gels were prepared by free-radical crosslinking copolymerization of N-isopropylacrylamide and N,N'-methylene(bis) acrylamide in water at fixed monomer and crosslinker concentrations. The equilibrium swelling ratio of the gels increases first slightly up to about 20°C then rapidly with increasing gel preparation temperature. Magnitude of the collapse transition in water at 34°C becomes larger as the gel preparation temperature increases. Calculations indicate a decrease in the effective crosslink density of PNIPA gels with increasing preparation temperature. The gels prepared at temperatures higher then 20°C were heterogeneous consisting of highly crosslinked regions interconnected by the PNIPA chains. Received: 3 May 2000/Revised version: 3 July 2000/Accepted: 17 July 2000     

Preparation of comb‐type grafted hydrogels composed of polyacrylamide and chitosan and their use for DNA adsorption

Comb‐type grafted hydrogels composed of polyacrylamide (PAAm) and chitosan (CT) were prepared and used for DNA adsorption. Instead of direct grafting of the acrylamide monomer onto the CT chain, semitelechelic PAAm with carboxylic acid end groups (PAAm–COOH) was synthesized by free‐radical polymerization with mercaptoacetic acid as the chain‐transfer agent, and it was grafted onto CT with amino groups. The synthesis of telechelic PAAm–COOH and the formation of comb‐type grafted hydrogels were confirmed by attenuated total reflectance/Fourier transform infrared spectroscopy and scanning electron microscopy measurements. The prepared comb‐type grafted hydrogels were used as sorbents in DNA adsorption experiments conducted at +4°C in a tris(hydroxymethyl)aminomethane/ethylenediaminetetraacetic acid solution of pH 7.4. DNA adsorption capacities as high as 2.0 × 10³ μg of DNA/g of dry gel could be achieved by the comb‐type hydrogels with higher PAAm contents. This value was approximately 6 times higher than that of CT alone. In addition, the comb‐type hydrogels showed a high adsorption/desorption rate depending on the PAAm content in the hydrogel. As a result, these comb‐type hydrogels carrying higher amounts of DNA may be considered good candidates for achieving higher removal rates for anti‐DNA antibodies and for effective gene therapy systems. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Removal of basic dyes from aqueous solutions by crosslinked‐acrylic acid/acrylamidopropane sulfonic acid hydrogels

In this study, Acrylic acid (AA)/2‐acrylamido‐2‐methlypropane sulfonic acid (AMPS) hydrogels were prepared by free radical polymerization in aqueous solutions of AA, AMPS, and N,N‐methylenebisacrylamide (NMBA) as crosslinker. Potassium persulfate (PPS)/potassium bisulfide (PBS) were used as initiator and accelerator pair. The water absorption capacities and dye adsorption properties of the hydrogels were investigated. Adsorption properties of the hydrogels were evaluated by depending on different adsorption conditions such as different initial dye concentration and contact time. The concentrations of the dyes were determined using UV/Vis Spectrophotometer at wavelength 530 nm for safranine T (ST) and 622 nm for brilliant cresyl blue (BCB). Adsorption kinetic studies showed that pseudo‐first order kinetic model is suitable to explain the adsorption kinetic data of the hydrogels. Langmuir and Freundlich isotherm models were used to describe adsorption data. The result revealed that the adsorption of basic dyes onto hydrogels fit very well both Langmuir and Freundlich isotherms. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reentrant phase transition and fast responsive behaviors of poly{N‐[3‐(dimethylaminopropyl)] methacrylamide} hydrogels prepared in poly(ethylene glycol) solutions

Macroporous temperature‐sensitive poly {N‐[3‐(dimethylaminopropyl)] methacrylamide} hydrogels were synthesized by free‐radical crosslinking polymerization of the monomer N‐[3‐(dimethylaminopropyl)] methacrylamide and the crosslinker N,N′‐methylenebisacrylamide in aqueous solutions at 22°C. Poly(ethylene glycol) (PEG) with a molecular weight of 1000 g/mol was used as the pore‐forming agent during the polymerization reaction. The concentration of PEG in the polymerization solutions was varied between 0 and 18 wt %, whereas the crosslinker (N,N′‐methylenebisacrylamide) concentration was fixed at 2 wt % (with respect to the monomer). The effects of the PEG concentration on the thermo‐induced phase‐transition behavior and the chemical structure, interior morphology, and swelling/deswelling kinetics were investigated. Normal‐type hydrogels were also prepared under the same conditions without PEG. An interesting feature of the swelling behavior of both the normal‐type and macroporous hydrogels was the reentrant phase transition, in which the hydrogels collapsed once and reswelled as the temperature was continuously increased. Scanning electron micrographs revealed that the interior network structure of the hydrogels prepared in PEG solutions became more porous with an increase in the PEG concentration in the polymerization solution. This more porous matrix provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved responsive rate to external temperature changes during the deswelling and swelling processes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009