The shear bond strength between enaeml and composite resin placed with an unfilled resin layer was tested under several conditions: The unfilled resin layer was either blown thin or left unthinned, and pre-cured alone or cured with the compsoite resin. Shear testing showed that the bond to enamel was slightly enhanced for Pekalux and was significantly enhanced for Durafill VS when the unfilled resin was not pre-cured. Thinning of unfilled resin slightly increased the bond strength of Pekalux and decreased the bond strength of Durafill VS. A majority of the specimens fractured at the composite resin-unfilled resin interface, and more than half of all interface failures occurred in specimens in which the unfilled resin had been pre-cured. The results indicated that the link between composite resin and the unfilled resin layer was enhanced by simultaneous curing.