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Objective: To evaluate the flexural strength, microleakage, and degree of conversion of a microhybrid resin polymerized with argon laser and halogen lamp. Method and Materials: For both flexural test and degree of conversion analysis, 5 bar samples of composite resin were prepared and polymerized according to ISO 4049. The halogen light-curing unit was used with 500 mW/cm² for 20 seconds and the argon laser with 250 mW for 10 and 20 seconds. Samples were stored in distilled water in a dark environment at 37°C for 24 hours. The flexural property was quantified by a 3-point loading test. For the microleakage evaluation, 60 bovine incisors were used to prepare standardized Class 5 cavities, which were restored and polished. Specimens were stored in distilled water for 24 hours at 37°C and thermocycled 500 times (6°C to 60°C). Specimens were then immersed in an aqueous solution of basic fuchsin for 24 hours. Longitudinal sections of each restoration were obtained and examined with a stereomicroscope for qualitative evaluation of microleakage. Fourier transform (FT)-Raman RFS 100/S spectrometer (Bruker) was used to analyze the degree of conversion. Results: ANOVA showed no statistically significant differences of flexural strength between the photoactivation types evaluated in the flexural study. Microleakage data were statistically analyzed by Mann-Whitney and Kruskal-Wallis tests. Enamel margins resulted in a statistically lower degree of leakage than dentin margins. No statistically significant difference was found among the 3 types of photocuring studied. ANOVA also showed no statistically significant difference in the degree of conversion among the studied groups. Conclusion: According to the methodology used in this research, the argon laser is a possible alternative for photocuring, providing the same quality of polymerization as the halogen lamp. None of the photocured units tested in this study completely eliminated microleakage. [ABSTRACT FROM AUTHOR]

The hybrid thin films cast on silicon wafers are used for evaluating the intermolecular associations between a cationic lipid and two model polymers. The mechanical approach for immobilization of the antimicrobial dioctadecyldimethylammonium bromide (DODAB) lipid in a polymeric network has represented a major improvement regarding its applications to produce antimicrobial coatings.

Objective. This study evaluated the impact of the distance between the light guide tip of the curing unit and material surface on the degree of conversion and Knoop microhardness of a composite resin. Materials and methods. Circular samples were carried out of a methacrylate micro-hybrid resin-based composite and light cured at 0, 2 and 4 mm distance. Monomer conversion rate was measured using a Fourier-transform Raman spectrometer and Knoop hardness number was obtained using a microhardness tester on the top and bottom surfaces. Data were statistically analyzed by analysis of variance and Tukey's test ( α = 0.05). Results. Overall, the increase of curing distance reduced the microhardness ( p ≤ 0.05), but did not influence the carbon double bond conversion rate ( p > 0.05) of the composite resin tested; and the top surface showed better properties compared to the bottom ( p ≤ 0.05). Conclusions. The light curing at distance can reduce mechanical properties and could affect long-term durability of the composite restorations. Thus, the use of a curing device with high irradiance is recommended. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the degree of conversion by Knoop microhardness (KHN) and FT-Raman spectroscopy (FTIR) of one nanofilled (Filtek Supreme-3M-ESPE [FS]) and one microhybrid composite (Charisma-Heraeus-Kulzer [CH]), each with different opacities, namely enamel, dentin, and translucent, which were photo-activated by a quartz-tungsten-halogen lamp (QTH) and a light-emitting diode (LED). Resin was bulk inserted into a disc-shaped mold that was 2.0 mm thick and 4 mm in diameter, obtaining 10 samples per group. KHN and FTIR values were analyzed by two-way ANOVA and Tukey's tests (α = 0.05). Nanofilled resin activated by a LED presented higher microhardness values than samples activated by a QTH for dentin opacity (p < 0.05). The microhybrid resin showed no differences in KHN or FTIR values with different activation sources or opacity. The nanofilled dentin and enamel resins showed lower FTIR values than the translucent resin. The KHN values of the translucent resins were not influenced by the light source. [ABSTRACT FROM AUTHOR]

Abstract: Thin films of mixtures containing carboxymethylcellulose acetate butyrate (CMCAB) and carbohydrate based surfactant, namely, sorbitan monopalmitate (Span 40) or poly(oxyethylene) sorbitan monopalmitate (Tween 40) were spin-coated onto silicon wafers. The effect of surfactant concentration on resulting film morphology and surface roughness was studied by atomic force microscopy (AFM). Upon increasing the concentration of Span 40 in the mixture, films became rougher and more heterogeneous, indicating surface enrichment by Span 40 molecules. In the case of mixtures composed by CMCAB and Tween 40, the increase of Tween 40 in the mixture led to smoother and more homogeneous films, indicating compatibility between both components. Differential scanning calorimetry (DSC) revealed that Span 40 and Tween 40 act as plasticizers for CMCAB, leading to dramatic reduction of glass transition temperature of CMCAB, namely, ΔTg =−158 °C and ΔTg =−179 °C, respectively. [Copyright &y& Elsevier]

Purpose: To evaluate early and 24-hour microtensile bond strength (μTBS) and the degree of conversion (DC) of one representative adhesive system from each of the four current bonding approaches. Methods: 40 human molars were sectioned occluso-gingivally into two halves. Resin composite was bonded incrementally to flat, mid-coronal dentin, using the adhesives Adper Scotchbond MP (MP); Adper Scotchbond 2 (SB); Clearfil SE Bond (SE); and Adper Prompt L-Pop (LP) according to the respective manufacturer's instructions (n= 10). One half was immediately sectioned into sticks and subjected to μTBS test. As the sectioning process took approximately 1 hour, the results were designated as 1-hour bond strengths. The other half was stored in distilled water at 37°C for 24 hours before being sectioned and tested. The DC of these systems was measured using Fourier Transform-Raman spectroscopy in three periods: immediately, 1 and 24 hours after polymerization. Data were analyzed with ANOVA and Tukey's tests. Results: There were no significant differences between the 1-hour and 24-hour bond strengths (P> 0.05), or among the DC measured immediately, 1 hour and 24 hours after polymerization (P> 0.05). However, significant differences were observed among adhesives (P< 0.05). μTBS values obtained, in MPa (1 hour/24 hour), were: SB (48.6 + 1.3/48.4 + 3.5) = SE (51.9 + 4.7/53.3 ± 2.9) > MP (35.3 ± 10.9/38.6 + 6.7) > LP (25.5 + 1.1/26.0 + 1.5). The DC, in percentage (immediately/lhour/24 hour), were: SE (81/82/87) > MP (79/77/81) > SB (60/63/65) > LP (39/37/42). [ABSTRACT FROM AUTHOR]

Abstract: Two room temperature ionic liquids (RTILs) without acidic protons, based on different cationic species (1-n-butyl-2,3-dimethylimidazolium) (BMMI) and N-n-butyl-N-methylpiperidinium (BMP) using (CF3SO2)2N− (TFSI) as anion, were prepared by quaternization of their respective amines with an appropriate alkyl halide, followed by ion exchange reaction. All relevant properties of these ionic liquids, such as, thermal stability, density, viscosity, electrochemical behavior, ionic conductivity and self-diffusion coefficients for both ionic species, were determined at different temperatures. In spite of their ionic conductivity being lower than 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonylimide) (BMITFSI), the absence of an acidic proton in both compounds is crucial to maintain their chemical stability towards metallic lithium and, thereby, to make possible the safe assembly of lithium ion batteries. Both ionic liquids without acidic protons do not react with metallic lithium; on the other hand, the formation of carbene species when BMITFSI was exposed to Li was confirmed by 1H and 13C nuclear magnetic resonance (NMR) and gas chromatography–mass spectrometry (GC–MS). [Copyright &y& Elsevier]

Structural changes were induced in a polyurethane elastomer by irradiating the film with UV light and the effects were monitored through birefringence measurements, thermal analysis and infrared spectroscopy. UV irradiation induces two competing effects: i) weakening and breaking of hydrogen bonding between the urethane groups, which improve the mobility of the hard segments and cause the glass transition temperature to decrease; ii) reticulation in the polymer network, causing the glass transition temperature to increase. For short periods of irradiation, up to four hours, breaking of H-bonds predominates and the birefringence increases. Upon further, prolonged irradiation, the effect from reticulation takes over and the birefringence decreases. [ABSTRACT FROM AUTHOR]

The vibrational spectra of Nafion® membranes with alkaline earth cations as counterions have been obtained by photoacoustic infrared spectroscopy (PAS–IR) and Fourier transform Raman spectroscopy (FT-Raman). The symmetrical stretching band of the sulfonate group (∼1060 cm-1) decreases with increasing atomic mass of the countercation, excepting for Mg2+, in both techniques. The thermal behavior of Nafion membranes by means of differential scanning calorimetry (DSC) curves showed a dependence on the water content and a similar profile between Nafion-Mg2+ and -Ca2+, and between Nafion-Sr2+ and -Ba2+, for the first scanning curve. An ageing effect was also observed on Nafion by DSC curves. High-resolution thermogravimetry (TG) curves under nitrogen atmosphere showed similar decomposition profiles. It was determined from TG curves that there is a decreasing water content with increasing ionic radius of cation, and the thermal stability increasing from Nafion-Mg2+ to -Ba2+. [Copyright &y& Elsevier]

Abstract: Ethylene glycol dimethacrylate (EGDMA) and/or triethylene glycol dimethacrylate (TEGDMA) oligomers formation was catalyzed in aqueous medium by horseradish peroxidase (HRP) in the presence of H2O2 at room temperature. EGDMA and/or TEGDMA oligomers were characterized by means of gel permeation chromatography, infrared vibrational spectroscopy and 1H NMR spectroscopy. Self-assembling of oligomers led to right-angled crystalline particles, as evidenced by scanning electron microscopy and differential scanning calorimetry. EGDMA, TEGDMA and EGDMA-co-TEGDMA oligomers synthesized in the presence of HRP–H2O2 system presented pendant vinyl groups along the chains, good solubility in chloroform, and well-defined melting point. These features evidenced few cross-linking or cyclization and revealed that the catalytic properties of HRP led to oligomeric materials with new characteristics. [Copyright &y& Elsevier]