Surface hardness of light-cured and self-cured composite resins

The surface microhardness of eight visible light-cured and self-cured composite resin materials was measured from 10 minutes after polymerization to 12 months. After the last measurement, a 250 microns layer was removed by grinding and the surface was reexamined. There was a progressive increase of microhardness for 4 weeks in all specimens (dry or wet), followed by stabilization. These results reflected the continual polymerization of composite resins after initial hardening for both self-cured and light-cured composite resins. The surfaces of specimens stored in water were softened compared with the surfaces of dry specimens. All the composite resins demonstrated substantially higher hardness after grinding, but different results among materials were attributed to varying compositions.