Disorders of Dental Hard Tissues Induced by Radioiodine-131 (I-131) Therapy Used in Differentiated Thyroid Cancer: An In Vitro Study

Abstract

This study aimed to evaluate, in vitro, the effects of I-131 on enamel and dentin in healthy human incisive permanent maxillary teeth. Our in vitro model analogue with the in vivo conditions of differentiated thyroid carcinoma patients treated with I-131, consisted in a solution of I-131 dissolved in artificial saliva. A total of 48 teeth were divided into eight groups (n = 6): control, irradiation groups at 3, 6, 12, 24, 36, 48, and 192 h, respectively. At the end of radiation exposure, radioiodine activity of specimens was assessed. Fine microstructure, nanostructure, surface roughness, and hidroxyapatite (HAP) crystallite diameter were investigated by atomic force microscopy (AFM) to both enamel and dentin structures. There is a constant increase of radioactivity in dental structures at 3, 6, 12, 24 h, due to progressive retention and I-131 migration, with a maximum at 36 h. Enamel showed notable alterations, which was correlated with the increase of the treatment time. A relevant visible distance between the HAP prisms was observed after 24 h. The surface suffered a loss in its compact structure. I-131 acts in the same way on HAP crystallites in dentin as in those in enamel. It was noticed that their morpho-dimensional changes occurred only after 12 h of treatment. Radioiodine-131 determines degradation of enamel and dentin by starting from the alteration of the crystalline network of HAP prisms, transforming them from compact materials into an agglomeration of rocky submicron structures.