Objectives: The aim of this study was to evaluate the influence of different restoration materials on demineralization on irradiated enamel and dentin. Methods: Thirty-two freshly extracted human third molars without caries were used. The teeth were assigned to four groups (n=8). Over the whole experimental period specimen were stored in 0.9% saline. All teeth were prepared with class II-cavities (mesial dentin, distal enamel). After preparation cavities were filled with four different materials (composite resin, amalgam, glass ceramic inlays and gold inlays). All teeth were bisected along their long axis in the middle of the fillings. One half of each tooth was irradiated with 60 Gy (2 Gy/ day for six weeks), the other half remained non-irradiated. All specimens were demineralized for 6 days with acidified gel (HEC, pH 4.8, 37 degrees C). From each tooth, two dentinal slabs were cut. The depth of the demineralized areas was determined using a polarized light microscope. Results: In all specimens lesion depth could be recorded. Significant higher lesion depths were found for the dentin and enamel in group AF+ (*p