Changes in Tooth Chemical Structure Following Radiotherapy

Based on our previous clinical study, there is a significant effect of tooth-level radiotherapy dose on dentition breakdown characterized by enamel shear fracture near the dentin-enamel junction (DEJ).  Objectives: To understand radiotherapy-induced effects on the chemical structure of teeth near the DEJ using micro-Raman spectroscopy.  Methods : Six paired, extracted human third molars were used with half of the teeth exposed to 70 Gy radiation and the other half to no radiation.  Following radiation, the crowns were sectioned buccolingually to produce a 2-mm-thick cross-sectional slice centered on the mesiobuccal and mesiolingual cusps. The sections were then polished sequentially with 600- and 1200-grit SiC paper and ChemoMet polishing cloth (Buehler Ltd). 2D-XY Raman mappings were carried out across the DEJ on the buccal and lingual surface of the exposed sections.  Raman images based on the ratio of carbonate (1070 cm^-1)/phosphate (960 cm^-1) and the peak width of 960 cm^-1 were obtained. Results : Carbonate/phosphate ratios indicated a decrease in carbonate content in enamel near the DEJ after 70 Gy radiation compared to the control group.  Changes in the 960 cm^-1 peak width at the same location indicated the degree of mineral crystallinity in that region decreased after radiation. Calculations based on individual spectra showed that the differences of carbonate content and degree of crystallinity were both significant (p<0.05). Conclusions : The preliminary results suggest that radiotherapy has a direct effect on the chemical structure of enamel near the DEJ.  These changes could be linked to the dentition breakdown that occurs following radiotherapy. Supported by NIH/NIDCR R01DE21462