INTERFACIAL BOND STRENGTHS OF AMALGAM BONDED TO AMALGAM AND RESIN COMPOSITE BONDED TO AMALGAM

Objective: The effects of time, surface preparation, and use of a bond ing agent on the ability to bond amalgam or resin composite to amalgam were studied. Method and materials: Cylindrical amalgam specimens wer e prepared in a split die (32 groups of 10 each). The 32 groups were d ivided into two groups of 16 each: amalgam bonded to amalgam and resin composite bonded to amalgam. One half of each group of 16 was bonded within 1 hour after the initial condensation (fresh) and the other hal f was bonded after 21 days' storage in physiologic saline (old). Four bonding methods (control [no bonding agent], Advance, All-Bond 2, or A malgambond Plus) were each utilized on one abraded group (air abrasion with 50-mu m aluminum oxide) and one unabraded group. After an additi onal 21 days of storage, bond strengths were measured with a three-poi nt flexure test. Solid amalgam cylinders were also tested. Results: So lid amalgam control cylinders exhibited mean bond strengths 10,000 psi greater than any of the bonded specimens. Among specimens of amalgam bonded to amalgam, those that were abraded after 21 days and used no b onding agent showed a significantly greater bond strength than did spe cimens utilizing any of the other combinations of the selected indepen dent variables. Among specimens of resin composite bonded to amalgam, those bonded after 21 days and utilizing a bonding agent exhibited sig nificantly greater bond strengths than did specimens utilizing any of the other combinations of the selected independent variables. Conclusi ons: The results of this in vitro study suggest that the strength of a repaired amalgam is only about 40% of that of an unrepaired amalgam. They also indicate that the strongest repair of amalgam using addition al amalgam material may be accomplished without the rise of any bondin g agents utilized in this study. When adding resin composite material to amalgam, the resin composite should be added after the amalgam has had adequate rime to set, and the use of a bonding agent increases the strength of the repair.