title: Radiotherapy effect on nano-mechanical properties and chemical composition of enamel and dentine.
abstract: OBJECTIVE
  To 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.
  
  
  METHODS
  Sections from seven non-carious third molars were exposed to 2 Gy fractions, 5 days/week for 7 weeks for a total of 70 Gy. 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 30 μm from the DEJ in enamel and dentine (E-500, E-30, D-30 and D-500).
  
  
  RESULTS
  The 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 (2931/430 cm(-1)) following radiation at all sites tested except at D-500, while the carbonate to phosphate ratio (1070/960 cm(-1)) increased at E-30 and decreased at D-500. Finally, phosphate peak width as measured by FWHM at 960 cm(-1) significantly decreased at both D-30 and D-500 following radiation.
  
  
  CONCLUSIONS
  Simulated 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.
authors.affiliation: Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, MO, United States.
authors.forename: R
authors.initials: R
authors.lastname: Reed
authors.affiliation: Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, MO, United States.
authors.forename: C
authors.initials: C
authors.lastname: Xu
authors.affiliation: Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, MO, United States.
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, MO, United States; Center of Excellencein Musculoskeletal and Dental Tissues, University of Missouri-Kansas City, MO, United States.
authors.forename: J P
authors.initials: JP
authors.lastname: Gorski
authors.affiliation: Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, MO, United States; Center of Excellencein Musculoskeletal and Dental Tissues, University of Missouri-Kansas City, MO, United States.
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri-Kansas City, MO, United States; Center of Excellencein Musculoskeletal and Dental Tissues, University of Missouri-Kansas City, MO, United States. Electronic address: walkermp@umkc.edu.
authors.forename: M P
authors.initials: MP
authors.lastname: Walker
mesh_terms: D003743:Dental Enamel / Q000737:chemistry* / Q000528:radiation effects*; D003804:Dentin / Q000737:chemistry* / Q000528:radiation effects*; D055119:Elastic Modulus; D006801:Humans; D008964:Molar, Third / Q000737:chemistry* / Q000528:radiation effects*; D009062:Mouth Neoplasms / Q000532:radiotherapy; D013059:Spectrum Analysis, Raman
keywords: Dentine–enamel junction; Enamel; Nanoindentation; Oral cancer; Radiotherapy; Raman microspectroscopy