An evaluation of four light-curing units comparing soft and hard curing.

Composite resin shrinks during polymerization producing marginal gaps around composite restorations. While incremental placement of composite resin has been used to control shrinkage, this technique is time consuming. Curing lights have been developed with varying outputs and curing cycles to speed curing and reduce marginal gaps in composite restorations. This investigation measured the marginal openings of Class V resin restorations cured with four different light-curing units. High-intensity curing units provided rapid curing to composite resin increments, but the two-phase curing cycle afforded significantly better marginal integrity than the other units.