[Effects of an incremental application technique on the polymerization of two light-activated composite filling...

The influence of the use of an incremental technique on the polymerization depth of two light-activated composite resins (hybrid composite resin, microfilled composite resin) was investigated in vitro. Of each of the two materials specimens were produced using variable increments and different polymerization times. Polymerization depth was determined by means of a microhardness tester (Vickers hardness). At the bottom of the cavity hardness values were significantly higher in samples produced in small increments (2 mm) than in samples with thicker layers (3 mm). A polymerization time of 20 s resulted in a significantly poorer polymerization at the bottom of the cavity than longer polymerization times. Hardness values decreased within each layer from the surface to the bottom. Irrespective of the material and the duration of illumination SEM pictures showed the presence of a line in the interface of the layers. The use of incremental technique in class II restorations resulted in differently polymerized zones that are exposed to the varying conditions of the oral cavity.