An in vitro study of the tensile strength of composite resins repaired with the same or another composite resin

Interfacial tensile bond strengths of self-cured and light-activated composite resins, repaired with the same or another composite resin, were measured. The bond strengths were measured as a function of age of the substrate or as a function of the adhered surface treatment. One control group of solid resin samples was tested for tensile strength. Other groups of specimens, matured for 48 hours, 7 days, and 1 year, were cut in half an d ground flat before a fresh mass of composite resin was added. Six groups were coated with a thin layer of intermediate resin or bonding aggent before the fresh composite resin was added. In general, the repaired composite resins revealed lower strength than did the cohesive samples, with bond strengths ranging from 19% to 52% of the strengths of the unrepaired resins. The intermediate resin increased the bond strength in all cases.