Effects of heterogeneous layers of composite and time on composite repair of porcelain.

Bond strengths of porcelain/composite resin repair samples, some homogeneous of conventional, hybrid, and microfill materials, some heterogeneous, made by incremental build-up of two of these composites, were evaluated. Samples were allowed to set without disturbance. After storage in 37 degrees C water for intervals of one day, seven days, and 28 days, the test samples were subjected to tensile force until fracture. There were significant differences in bond strengths of homogenous and heterogeneous samples after different storage periods. All mean repair bond strengths were significantly less at seven days than at one or 28 days. Heterogeneous repairs with larger-particle-size composite at the porcelain interface and overlayed with smaller-particle-size composites resulted in higher bond strengths than the homogeneous small-sized composite repairs. Failures of the repairs occurred at the porcelain/composite interface in a statistically significant number, implying that technique exactness at the interface plays an important role in the success of the technique.