Effect of gamma radiation on human enamel chemical and physical properties

Background: Gamma radiation is still used in developing countries for head and neck cancer treatment. Irradiated dental enamel undergoes dose-dependent chemical and mechanical changes that can hinder oral rehabilitation. Understanding these processes can be useful to professionals to plan safer long-lasting treatments. This study aimed to evaluate 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 dose: 0; 20; 40; 50; 60; or 70 Gy, in daily increments of 2 Gy. After irradiation, the composition and carbonate/ phosphate ratio (C: P) were evaluated by Fourier Transformed Infrared Spectroscopy (FTIR). X-ray diffraction (XRD) was used to evaluate 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 of C: P, crystallinity (%), shape factor (nm), hardness (VHN - Vickers Hardness Number), and elastic modulus (GPa - Gigapascals) were submitted to analysis of variance and to Tukey’s test (α = 0.05). Results: FTIR showed carboxylic acid in the irradiated groups and an increase in C: P for the 70 Gy group (p = 0.015), but with no change in crystalline structure. A significant decrease was observed in the values of hardness (p = 0.0000) and the elastic modulus (p = 0.0000) in the irradiated groups. For scratch test, the 60 and 70 Gy groups showed lower values for initial spallation. SEM showed spaced rounded peaks of enamel prisms in the 60 and 70 Gy groups. Conclusions: Gamma radiation negatively affected the chemical and physical properties of human enamel. Trial registration: Plataforma Brasil, CAAE: 66495417.1.0000.007.