Objectives: The aim of this study was to evaluate the influence of different restoration materials on demineralization on irradiated dentin. Methods: 55 freshly extracted human third molars without caries were used. Over the whole experimental period specimen were stored in 0.9% saline. Dentin disks were prepared. The 55 disks were assigned to five groups (n=11) including a positive and negative control. After preparation in three groups occlusal restorations with different materials (amalgam, base metal alloy, titanium alloy) were fabricated. Four groups were irradiated with 60 Gy (2 Gy/ day for six weeks), the negative control group remained non-irradiated. All specimens were demineralized for 14 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. Statistical analysis showed a significant influence of irradiation and the used material (p 0.001, ANOVA). Between both control groups (C, C60) no significant differences could be detected (p> 0.05, Tukey test). Between the controls and the restored groups significantly increased lesion depths could be observed (p 0.05, Tukey test). Pairwise comparison between the three materials showed no significant differences (p> 0.05, Tukey test). Conclusion: Irradiated Dentin with metal restorations showed the significantly highest lesion depths after initial demineralization by acidified gel compared to the control groups. The different metal materials had no significant impact on artificial dentin demineralization. Keywords: restorative materials, irradiation, demineralization