27 Organic solvents have the ability to http://www.selleckchem.com/products/Bosutinib.html penetrate and swell the polymer network, facilitating the liberation of unreacted and leachable monomers. As the solvent penetrates the matrix and expands the openings between polymer chains, oligomers diffuse out.27 Intraoral fluids represent solvents probably somewhere between the more aggressive organic solvents and water; the US FDA recommends a 75% ethanol�Cwater solution as a food/oral-simulating liquid in order to be clinically relevant.23 Therefore, in the present study, 75% ethanol-25% deionized water was used as an extraction medium to measure monomer release. Adequate polymerization is crucial in obtaining optimal physical properties and clinical performance of resin composites.

31 Ideally, a dental restorative resin might have all of its monomers converted to polymers during the polymerization reaction. Dual-cure materials are intended to be more effective in the early stages of polymerization because they contain both photoinitiators and components for a chemically activated reaction. Braga et al32 investigated the early shear strength of porcelain-dentin bonding using dual-cure cements at 10, 30, and 90 min and reported significant differences between 10 and 30 min. Krishnan et al33 reported that the solubility of visible light-cured dental composite was found to increase with time in their study on the effect of diluents on the properties of a visible light-cured dental composite at specific intervals of 1, 7, 14, 21, 28, and 30 days. In addition, Kavara et al34 investigated the elution of residual monomers by HPLC analysis at time intervals of 1, 3, 6, 12, and 24 hours and 3, 7, and 14 days.

To determine early and late elution of monomers from dual-cured resin cement, the time intervals of 10 min, 1 hour, and 1, 3, 7, 14, and 21 days were determined. Molecules of high molecular weight, base monomers such as Bis-GMA and UDMA, however, decompose in gas chromatographs and only the decomposition products of these are detectable.16 For this reason most studies on large monomers have been analysed by HPLC,10,13,16 which is preferred to gas chromatography because it provides a greater level of control over the separation process, in this case since the monomers are soluble in the mobile phase.11 HPLC analysis was used in this study to evaluate monomer release from resin cements because it is a very powerful and commonly used separation method.

The polymer network is composed of cross-linked molecules within which the unreacted monomers reside. As the solvent penetrates the matrix and expands the openings between polymer chains, monomers diffuse out. Although complete saturation of the composite with solvent requires weeks or months as a result of the slow nature of the diffusion of chemicals into the cross-linked resin matrix, elution appears to be completed AV-951 within days because subsequent weight changes are so small as to be almost immeasurable.