The newer materials incorporate many of these features, but no material incorporates them all. This fact is sufficient reason to examine these materials more closely. The purpose of this Clinical Update is to review the clinical use of bases and liners and to offer clinical guidelines for their use. The definitions of bases and liners vary greatly in the literature. Most reasons to use liners or bases are empirical rather than scientific.
Thermal insulation is short-lived.
Bases and liners also can provide a vehicle for delivering therapeutic agents, ensuring optimal thickness of resin and porcelain posterior restorations and, more recently and more importantly, sealing dentinal tubules to increase the tooth's resistance to microleakage. Many different materials have been and are being used as liners and bases beneath direct restorations. With the advent of dentin bonding agents, a micromechanical bond to tooth structure through the formation of a hybrid layer of resin-impregnated dentin can be realized. These agents have been used routinely for the past 10-15 years under composite resin restorations. They are not a substitute for sound principles of cavity preparation.