Structural, compositional, and mechanical assessment of human root dentin following ionizing radiation exposure in head and neck cancer tomotherapy.

Abstract

Human root dentin may undergo direct physicochemical, microstructural, and mechanical alterations during radiotherapy for head and neck cancer. In this study, healthy third molars were irradiated under tomotherapy-like conditions using a clinically inspired fractionated protocol of 2 Gy per day for 10, 20, and 30 days, reaching cumulative doses of 20, 40, and 60 Gy, together with a non-irradiated control group. Root dentin was characterized using Raman spectroscopy, atomic force microscopy, X-ray diffraction, scanning electron microscopy, and microtensile testing. Raman spectroscopy showed preservation of the main mineral and organic bands, but the CO₃/PO₄ and Amide I/PO₄ ratios decreased with irradiation, indicating changes in the mineral-matrix balance. AFM showed no major nanoscale topographic alterations, although AFM showed heterogeneous local Young's modulus distributions, with higher central values in the irradiated groups but no statistically significant differences from the control. XRD confirmed preservation of the apatite phase without formation of new crystalline phases, while Rietveld refinement revealed subtle anisotropic lattice changes, particularly an increase in parameter a. SEM showed localized surface irregularities, less defined tubule borders, and partial tubular obstruction in selected irradiated fields. At the functional scale, microtensile testing revealed reductions in microtensile strength and strain at failure. These findings indicate radiation-associated multiscale alterations in root dentin, including relative changes in mineral-organic organization, localized microstructural differences, and reduced mechanical performance.