The aim of the present in vitro study was to evaluate the marginal adaptation and seal of direct and indirect (inlay) Class II resin composite restorations made with Z100/Scotchbond MP or Herculite/Optibond. The quality of margins in dentin was assessed for restorations made with or without a lining of glass-ionomer cement or resin-modified glass-ionomer material. The restored teeth were submitted to thermocycling and then to replication for scanning electron microscopic observation and to a dye infiltration test. In the present test conditions, the inlay technique proved its superiority over the direct restorative method. The quality of the dentinal margin of restorations made with Z100/Scotchbond MP appeared also slightly better. Both the glass-ionomer cement and the resin-modified glass-ionomer material, when applied as a lining, increased leakage and downgraded marginal adaptation. The full bonding with modern adhesives appeared to be the most efficient way to enhance the marginal quality of both direct and indirect restorations.