Radiotherapy effect on nano-mechanical properties and chemical composition of enamel and dentine

Abstract

ObjectiveTo understand radiotherapy-induced dental lesions characterized by enamel loss or delamination near the dentine–enamel junction (DEJ), this study evaluated enamel and dentine nano-mechanical properties and chemical composition before and after simulated oral cancer radiotherapy. DesignSections from seven non-carious third molars were exposed to 2Gy fractions, 5 days/week for 7 weeks for a total of 70Gy. Nanoindentation was used to evaluate Young's modulus, while Raman microspectroscopy was used to measure protein/mineral ratios, carbonate/phosphate ratios, and phosphate peak width. All measures were completed prior to and following radiation at the same four buccal and lingual sites 500 and 30μm from the DEJ in enamel and dentine (E-500, E-30, D-30 and D-500). ResultsThe elastic modulus of enamel and dentine was significantly increased (P≤0.05) following radiation. Based on Raman spectroscopic analysis, there was a significant decrease in the protein to mineral ratio (2931/430cm−1) following radiation at all sites tested except at D-500, while the carbonate to phosphate ratio (1070/960cm−1) increased at E-30 and decreased at D-500. Finally, phosphate peak width as measured by FWHM at 960cm−1 significantly decreased at both D-30 and D-500 following radiation. ConclusionsSimulated radiotherapy produced an increase in the stiffness of enamel and dentine near the DEJ. Increased stiffness is speculated to be the result of the radiation-induced decrease in the protein content, with the percent reduction much greater in the enamel sites. Such changes in mechanical properties and chemical composition could potentially contribute to DEJ biomechanical failure leading to enamel delamination that occurs post-radiotherapy. However, other analyses are required for a better understanding of radiotherapy-induced effects on tooth structure to improve preventive and restorative treatments for oral cancer patients.