The extent of polymerization of Class II light-cured composite resin restorations; effects of incremental placement technique, exposure time and heating for resin inlays.

The extent of polymerization of light-cured composite resins cured in relatively large class II cavities was estimated by measuring Knoop hardness on sectioned surfaces of resin restorations. The influences of the incremental placement technique, exposure time, and post-curing of resin inlay on the extent of polymerization of two different resin materials were examined. For both MFR type (HE) and hybrid type (P50) materials, the 3-step incremental placement technique was superior when the cavity was restored by the direct filling method. For resin inlays, the post-heating improved the conversion of resin restorations. However, because the final degree of conversion of resin attained by heating was influenced by the initial conversion of the resin at the stage of light-curing, the 2-step incremental placement technique was recommended at the light-curing stage for even resin inlays. As the exposure time is influenced by the transmittance of material and the intensity of activator light, it should be optimized in accordance with manufacturers' directions.