Dentinal bonding agents (BAs) have recently been developed to improve the clinical performance of dental light-cured restorative composite resins. The aim of this study was to evaluate in vitro the newest generation of BAs which are composed of HEMA (Hydroxy-ethyl-methacrylate), urethane diacrylate or cross-linked aromatic dimethacrylates (BIS GMA). Marginal microleakage tests, scanning electron microscopy (SEM) and shear bond strength tests were made to evaluate the interface between dentin and composite materials. Marginal microleakage tests revealed dye penetrations in a large number of composite resin restorations, while SEM demonstrated the presence of marginal gaps and fractures along the interface between dentin and composite materials. Shear bond strength tests demonstrated that BAs are able to bond the dentin surface.