The effect of the pulse-delay cure technique on residual strain in composites.

Polymerization-induced shrinkage of composites leads to residual stress in the final restoration. For composites with a high modulus of elasticity, the level of stress can have significant clinical consequences, including crack formation in the enamel or microscopic separations at the preparation/restoration interface. The pulse-delay cure technique cures composites by providing low-energy pulse initially (e.g., 200 mW/cm2 for 3 seconds), followed by a waiting period of 3 to 5 minutes for strain relief, during which the composite can be finished and polished. The final cure is obtained by exposure to a high-intensity light source of 500 mW/cm2 for the recommended time. In vitro data obtained by strain gauges show that the pulse-delay cure technique can reduce residual strain in the composite by as much as 34%.