Effects of organic solvents on the depth-of-cure determination of conventional and bulk-fill resin composites.

This study investigated the influence of organic solvents on the depth of cure (DOC) of resin composites. Two conventional (Filtek Universal [FU] and Beautifil II [BE]) and two bulk-fill (Filtek One Bulk Fill [FO] and Beautifil-Bulk [BB]) composites were evaluated. Cylindrical specimens were fabricated using polyvinylsiloxane molds, light-cured according to the manufacturers' recommendations, and immersed in one of four solvents: acetone, chloroform, ethanol (ETH), or tetrahydrofuran, for 48 h at 22°C (n = 10/composite/solvent). Specimens were imaged under a digital microscope, and the thicknesses of the "solvent-resistant" and "solvent-affected" zones, as well as the percentage of solvent-affected area, were measured with imagej. Knoop microhardness was measured at the top and at 1-mm intervals down to 5 mm (conventional) or 7 mm (bulk-fill). The "solvent-resistant" zone ranged from 3.1 to 4.3 mm for conventional and from 4.9 to 6.9 mm for bulk-fill composites. ETH produced the smallest solvent-affected area for all composites. The 80% bottom-to-top microhardness ratio was reached at 2.6-3.4 mm for conventional, 3.6-4.2 mm for FO, and 2.9-3.3 mm for BB. The resin composite and the organic solvent influenced the determination of DOC, and ETH was the least effective solvent.