The bond strength of incrementally placed composite resins

The bond strength of the junction of various incremental combinations of four resin based restorative materials was tested. Rods of composite suitable for transverse strength testing were prepared in two parts; the first part of a mould was filled with composite and cured against a highly polished amalgam surface or in air. The second part of the mould was filled with composite and cured against the end of the first part composite. The prepared specimens were fractured employing three-point loading in a mechanical testing machine.
When specimens consisting of two parts of the same material were joined, the bond strength was better when the first part was set in air. The strength of the bond between two different products was, in most cases, in the order of 55 per cent to 100 per cent of the transverse strength of the weaker of the pair. The bond strength depended on the nature of the surface of the first part of the specimens as well as the material combinations used. For all material combinations, a better bond was obtained if the two materials joined had similar curing systems.