Dental amalgam does not by itself bond to tooth structure. This was recognized as a shortcoming by early practitioners such as Baldwin. He recommended that the prepared cavity be coated with zinc phosphate cement just prior to filling with amalgam, in order to improve the seal and retention. The practice did not become universally accepted and eventually fell into disuse. Until the 1980s, most amalgam restorations placed worldwide were done without adhesives, although in the 1970s a polycarboxylate-based adhesive liner was formulated specifically for this purpose In the mid-1980s the first reports of the use of resins to bond amalgam to etched tooth structure, much like is done for composite resins, appeared in the literature. Since then, a number of papers have been published on laboratory as well as clinical studies of the technique. For large cavity restorations, features such as pins, slots, holes and grooves can be used for the retention of large amalgam restorations, but they do not reinforce the amalgam or increase its strength.
