Effect of Radiotherapy on Nano-mechanical Properties and Chemical Composition of Tooth Enamel and Dentin

The purpose of this study was to understand radiotherapy-induced dental lesions characterized by enamel delamination near the dentin-enamel junction (DEJ) by evaluating enamel and dentin nano-mechanical properties and chemical composition before and after in vitro and in vivo radiotherapy. For the in vitro group, sections from non-carious third molars were exposed to 2 Gy fractions, 5 days/week for 7 weeks for a total of 70 Gy. For the in vivo group, five teeth extracted from three patients who had previously undergone radiotherapy for head or neck cancer were collected, all teeth had doses greater than 60 Gy. Nanoindentation was used to evaluate modulus and hardness, 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 in vitro simulated radiation and after in vivo radiation at the same four buccal and lingual sites 500 and 30 microns from the DEJ in enamel and dentin (E-500, E-30, D-30 and D-500). With significance set at P≤0.05 across testing, the modulus and hardness of enamel and dentin significantly increased following in vitro and in vivo radiation at all locations. Following in vivo radiation, there was a significant decrease in the protein/mineral ratio, the