Formulation and Characterization of Experimental Adhesive Systems Charged with Different Concentrations of Nanofillers: Physicomechanical Properties and Marginal Gap Formation

This study aimed to formulate and characterize experimental dental adhesives charged with different concentrations of nanofillers. Different concentrations (0, 7.5 wt%, and 15 wt%) of nanosized silica (50 nm) were added to the bond of a two-bottle experimental etch-and-rinse adhesive system (EA0, EA7.5, and EA15). The following physicomechanical properties were evaluated: degree of conversion (DC%), ultimate tensile strength (UTS), flexural strength (FS), static modulus of elasticity (SME), dynamic modulus of elasticity (DME), and glass transition temperature (Tg). Marginal integrity (%MG) was evaluated in standardized class I cavities hybridized with the EAs and restored using two dental composites (CON-conventional and OBF-bulk-fill): EA0CON, EA7.5CON, EA15CON, EA0OBF, EA7.5OBF, and EA15OBF. Gap formation was measured in the occlusal and mesial tooth-restoration interfaces using a 3D laser confocal microscope. Microtensile bond strength (mu TBS) was evaluated using dentin-composite beams (1 x 1 mm) obtained from restorations. Data were submitted to ANOVA and Tukey's test (alpha = 0.05). For DC% and Tg, EA15 < EA0 = EA7.5 (p < 0.05). For UTS, EA0 < EA7.5 < EA15. For FS, SME, and DME, EA0 < EA7.5 = EA15 (p < 0.05). For the gap formation analysis, there were statistical differences only for the conventional composite (EA0CON > EA7.5CON = EA15CON). The lowest values (p < 0.05) of mu TBS were observed for the groups restored with EAs without inorganic content. In conclusion, charging dental adhesives with nanofillers may be a suitable strategy for improving their properties as well as their interaction with dental substrates.