This study compared the marginal leakage of temporary restorations using Cavit, IRM, zinc phosphate cement (ZPC), and copper bands cemented with ZPC. Standardized complex endodontic access preparations were made in 176 extracted human molars. The teeth were divided into six groups, including positive and negative controls. A Universal matrix system was placed over each tooth before restoration, except in the copper band group, in which teeth were restored with ZPC after copper band cementation. Marginal leakage was evaluated with a binocular microscope after the teeth were immersed in artificial saliva, colored with 2% methylene blue and buffered to neutral pH, at 37 degrees C for various time intervals after thermal cycling. In the experimental groups, the differences in the leakage scores of the Cavit group and the other groups were very marked. The Cavit group presented the least marginal leakage, irrespective of time, whereas more than half the specimens from the IRM, ZPC, and copper band groups displayed severe leakage from day 1.