Pulse activation: reducing resin-based composite contraction stresses at the enamel cavosurface margins

To evaluate the effect of pulse activation light-curing of resin-based composites on the stress reduction at the enamel surface.

The rate of polymerization of a resin-based composite known to be accompanied by high contraction stress was examined by its surface hardness. The effects of polymerization stresses were examined with the use of dye penetration along enamel margins in cavities with a C-factor of 5. The occlusal-most layer of resin-based composite was polymerized at different power densities and time intervals; 40 s@600 mW/cm2, 40 s@100 mW/cm2 and pulse activation; 2 s@300-350 mW/cm2, followed by additional exposure of 10 s@600 mW/cm2. Diametral tensile strengths were measured for each parameter.

The surface hardnesses of both the 40 s@600 mW/cm2 group and the 40 s@100 mW/cm2 group developed at nearly the same rate. The surface hardness of the pulse activated group developed appreciably slower. The diametral tensile strengths of all three groups were not significantly different. There was significantly less dye penetration with the use of the lower power density but there was very little leakage noted with the pulse-activated group. It is believed that this is the result of a prolonged gel state, which allowed flow to occur in the resin-based composite. There is significant clinical potential for the use of pulse activation of light-cured resin-based composite materials.