Visible light-polymerized resin composite tabs were bonded to the flattened, acid-etched surface of teeth that were scheduled for extraction. Half of the teeth (group I) were isolated with cotton rolls in conjunction with a saliva ejector. The remaining teeth (group II) were isolated using a rubber dam. Both methods of isolation were used for each patient so that to some extent all patients served as their own controls. Following extraction, all samples were thermocycled 500 times alternating between 6 degrees C and 60 degrees C, after which they were immersed in 5% methylene blue for 4 hours. Each tooth was then mounted in acrylic resin and sectioned on a hard tissue microtome. Microleakage was assessed using a light microscope at x 20 magnification. The use of rubber dam isolation resulted in less microleakage at the enamel resin interface.