Effect of Different Placement Techniques and Curing Methods on Composite Microhardness in Class I Restorations

Statement of problem: The polymerization of light cured composite resins is initiated fromsurface layer and the rate of polymerization reduces from surface to depth. The difference in hardness is in correlation with different factors such as the intensity of unit and the distance between composite and light tip.

The aim of this study was to compare the effect of four different methods of filling and two light direction on microhardness of class I composite resin restorations.

In this parallel interventional study, 40 intact human premolarteeth were selected. Class I cavities were prepared (4×4×4 mm). After etching and applying Excite as a dentin adhesive, the specimens were divided into four groups (n=10) based on the filling

Group 1)one bulk, group 2)horizontal incremental and occlusal light curing, group 3)horizontal incremental and three directional light curing, Group 4)oblique and three directional light curing. Z100 was used for restoration of cavities. Microhardness of specimens was measured by kicker's microhardness tester in 0, 1.5, 2.5 and 3.5 mm distance from surface. Data were analyzed using ANOVA and Duncan tests (=0.05).

The mean value of microhardness in groups 1 and 2 showed significant differencefrom that of groups 3 and 4 (p<0.05). Within each group, the subsurface layer showed the highest value of hardness (P<0.05) except for group 2 that all surfaces showed a similar hardness value (p>0.05).

Based on the results of this study, incremental technique (oblique or horizontal) with three dimensional light curing is the most suitable procedure for obtaining a maximum hardness in Class I composite resin restoration.