Various amounts of microfiller, condensed microfiller, prepolymer plus microfiller, or macrofiller were added to an unfilled light-curable resin. The marginal adaptation of these experimental resin/filler mixtures was studied by measuring the wall-to-wall polymerization contraction (wtw-contraction) in dentin cavities in vitro. The investigation showed that increasing amounts of microfiller did not affect the wtw-contraction. However, mixtures made by the three other fillers showed a decreasing wtw-contraction with increasing filler concentration.