The marginal seal of four temporary filling materials in endodontic access cavities was examined in vitro after thermocycling and mechanical loading using dye penetration tests and a quantitative marginal analysis of replicas in the SEM. Class I cavities were prepared in 44 extracted human molars and filled either with Cavit, Kalsogen, IRM, or TERM. After setting the reaction and thermocycling procedure, Cavit showed less microleakage in the dye penetration test and fewer marginal crevices in the quantitative marginal analysis. After loading, two Cavit fillings collapsed into the endodontic cavity. The marginal conditions of TERM were comparable to Cavit after thermocycling and mechanical loading. Kalsogen and IRM restorations demonstrated significantly increased microleakage and a higher percentage of marginal crevices after thermocycling and loading. In contrast to dye penetration tests, the effects of different factors on the marginal integrity of temporary fillings can be examined with the replica technique and quantitative marginal analysis.