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.