Effect of gamma radiation on human enamel chemical and physical properties

Abstract

Background: Gamma radiation is still used in developing countries for the treatment of head and neck cancer. Irradiated dental enamel undergoes dose-dependent chemical and mechanical changes that can hinder oral rehabilitation. Understanding these processes can help professionals plan safer and longer-lasting treatments. This study aimed to evaluate the effects of different doses of gamma radiation on the chemical and mechanical properties of human dental enamel. Methods: Sixty human third molars were divided into six groups (n = 10) according to radiation dose: 0, 20, 40, 50, 60, or 70 Gy, administered in daily fractions of 2 Gy. After irradiation, enamel composition and the carbonate-to-phosphate ratio (C:P) were evaluated by Fourier Transform Infrared Spectroscopy (FTIR). X-ray diffraction (XRD) was used to assess crystal size (shape factor) and crystallinity. Hardness, elastic modulus, and scratch resistance were measured, and the microstructure was observed by scanning electron microscopy (SEM). Data for C:P, crystallinity (%), shape factor (nm), hardness (VHN – Vickers Hardness Number), and elastic modulus (GPa) were submitted to analysis of variance and Tukey’s test (α = 0.05). Results: FTIR revealed the presence of carboxylic acid groups in the irradiated samples and an increase in the C:P ratio for the 70 Gy group (p = 0.015), although no changes were observed in the crystalline structure. A significant decrease in hardness (p = 0.0000) and elastic modulus (p = 0.0000) was observed in the irradiated groups. In the scratch test, the 60 and 70 Gy groups showed lower values for initial spallation. SEM images revealed spaced and rounded enamel prism peaks in the 60 and 70 Gy groups. Conclusions: Gamma radiation negatively affected the chemical and mechanical properties of human dental enamel.