Radiotherapy compositional and mechanical effects evaluation in radicular dentin by FTIR spectroscopy and microhardness testing

Head and neck cancers are responsible for 400 to 600 thousand of new cancer cases per year over the world, presenting a mortality rate of 223 to 300 thousand per year. Radiotherapy can be used as a definitive, adjuvant or palliative treatment. One of the radiotherapy indirect side effect is the radiation-related caries, characterized by presenting a painless, rampant and rapid progression. Hard tissues can be affected by the ionizing radiation, changing their composition, morphology and mechanical properties, although there is a lack of studies relating these changes with radiation caries. Thus, considering that radicular dentin is a tissue with a high incidence of radiation caries, this study aimed to evaluate the compositional and mechanical changes of this tissue when submitted to radiotherapy. To that, it was conducted an in vitro study with 45 bovine teeth roots, where 90 radicular dentin slabs of 4 x 4 cm were obtained. The samples were immersed in artificial saliva and submitted to radiotherapy using cobalt-60, simulating doses for head and neck cancers of 2 Gy per day per 6 weeks, accumulating a total of 60 Gy. FTIR spectroscopy and microhardness testing were performed before and after the radiotherapy. The spectra were analyzed in six IR fingerprint bands: amide I, amide II, amide III, phosphate, carbonate V2 and carbonate V3V4. Statistical analysis was performed by Student's t-test and Wilcoxon test, considering the level of significance of 5%. The carbonate V3V4 and the amide III areas decreased after the radiotherapy, presenting significant statistical difference between both periods. These findings can be related to inorganic and organic changes due to free radicals formation. The Knoop microhardness value decreased after the radiotherapy, also showing statistical difference, which can be associated to collagen reorganization or denaturation and to inorganic changes, leading the tissue to be more prone to cracks formation. It can be concluded that the radiotherapy affects the compositional and mechanical properties of the radicular dentin, and this fact should be considered in future studies.