Introduction: Endodontic treatment requires the temporary closure of access opening. There is a large offer of different materials on the market. Objectives: The aim of the study was to find a microscopic method of teeth preparation suitable for evaluation of marginal seal quality of temporary fillings. Material and methods: Cavities of class I and V were filled with different temporary filling materials (zinc-oxide cement, Cavit, Caviton, GIC). The dye penetration method (methylene blue) was used. Preliminary investigation - fractured surfaces of teeth were not suitable for detailed investigation under SEM. 1. The teeth were cut using Accutom 50 (Struers), embedded into acrylic resin, ground and polished for microstructural analysis. 2. The teeth were embedded into acrylic resin, then cut using Accutom 50, ground and polished for microstructural analysis. 3. The teeth were embedded under vacuum into slow-setting epoxy resin, then cut using Accutom 50, ground and polished for microstructural analysis. Results: The results obtained in the preliminary study were not satisfactory; analysis under SEM was not possible. Methods 1 and 2 allowed the investigation under SEM nevertheless it was very difficult due to the presence of many artificial cracks. Quality of the surface obtained by method 3 was very good, without any cracks or voids and it can be recommended for further detailed studies on quality of temporary filling marginal seal. Conclusion: The method of sample preparation using vacuum system was found the most suitable for marginal seal evaluation. Supported by the project 1M0528 and grant No.106/09/H035. Keywords: filling materials, marginal seal, dentistry, light microscopy, SEM, dye penetration, temporary fillings