Objectives:The aim of this study was to evaluate the effect of different irradiation doses on microtensile bond strength (mTBS) of four different dentin adhesives/compomer combinations1,2,3,4 on perfused primary dentin in vitro. Materials and methods: 144 freshly extracted primary molarswere included. All teethwere specially prepared allowing the simulation of dentin perfusion and standardized conditions. According to four different dentin adhesives and three irradiation doses (0 Gy, 6 Gy and 60 Gy), the specimens were randomly assigned to 12 experimental groups of 12 each: Syntac (S0, S6, S60), Prime&Bond (P0, P6, P60), Futurabond (F0, F6, F60), Optibond (O0, O6, O60). Each specimen was irradiated fractionally with 2 Gy/day (6mV, X-Ray) using a linear accelerator, respectively, depending on the experimental irradiation dose group. All materials were applied as recommended by the manufacturer. Microtensile bond strength was measured 15 min after application of the fissure sealant using a universal testing machine. Statistical analysis was performed using SPSS 15.0. Results: Statistical analysis showed a significant influence of irradiation on microtensile bond strength (p 0.001, ANOVA). The highest mTBS were found in the non-irradiated groups (S0, P0, F0, O0), the lowest mTBS were observed in specimens irradiated with 60 Gy (S60, P60, F60, O60). Comparison of the dentin adhesives in non-irradiated groups showed significant higher values in specimens treated with Optibond compared to group S0 (p 0.05, Tukey's test). Between groups S0, P0 and F0 no significant difference could be detected (p > 0.05, Tukey's test). The influence of irradiation was significant in the 60 Gy groups except for Syntac (Tukey's test, p 0.05). Irradiation doses of 6 Gy did not show any significant influence compared to non-irradiated groups (0 Gy). Conclusions: Within the limitations of this in vitro investigation it can be concluded that irradiation of primary teeth in doses of 60 Gy might affect microtensile bond strength of dentin adhesive/compomer combinations.