Introduction: Clinical radiotherapy is one of the most important techniques for the treatment of malignant lesions in head and neck; however, exposure to ionizing radiation may lead to both systemic and local complications, immediately and after this treatment, where the main issue is the xerostomia and its consequent oral mucositis. Regarding late complications produced by radiation, decay of radiation and osteoradionecrosis, both dosedependent lesions, showed a high level of incidence in recent decades and it would be difficult to manage, although patients referred after treatment’s completion and under the influence of local factors. Methodology: Then, This study evaluated the effect of ionizing radiation from gamma source onto samples of enamel, root dentin and jawbone samples undergone to the same absorbed dose / dose rate that those in patients with head and neck cancer. The non-irradiated and irradiated samples were analyzed by microhardness surface analysis; scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR). Results and discussion: Microhardness data were analyzed statistically with a confidence level of 95% (p value <0.05%), using parametric Student’s t-test for related averages and ANOVA statistical test, finding a statistically significant result (p = 0.00) to all four groups samples. Conclusion: It was observed a high deleterious and statistical significant effect of gamma radiation on hard tissues from oral cavity, regarding to physical, compositional and morphological properties.