Bonding fresh amalgam to existing amalgam: a shear and flexural strength study.

The purpose of this study was to compare the shear and flexural strength obtained when various adhesives or liners were used to bond freshly placed amalgam to existing amalgam. The adhesives used in this study were the following: cavity varnish, 4-META adhesive (Amalgambond), and a dentin bonding agent (Clearfil New Bond). After samples were fabricated, shear bond strengths were determined by using an Instron Testing Machine, and flexural strengths determined using a Material Test System (MTS) testing machine. All test groups produced shear and flexural strengths less than one half of the control group. The dentin bonding agent and the 4-META adhesive produced significantly higher shear and flexural strengths than the test group in which no lining material was used.