Direct radiation-induced effects on dental hard tissue

TLDR

Radiation caries, a complication of radiotherapy, manifests as enamel erosion and dentin exposure, yet the underlying mechanisms remain poorly understood. This study aimed to assess the direct effects of radiation on dental hard tissue and their contribution to radiation caries development. Sixty extracted third molars were irradiated at 0, 30, or 60 Gy, after which microhardness, elastic modulus, microstructure, crystal properties, and protein/mineral ratios were measured using Vickers microhardness testing, AFM, SEM, X‑ray diffraction, and Raman spectroscopy. Radiation exposure decreased enamel microhardness and elastic modulus at 50 µm from the DEJ, caused interprismatic destruction and fissures, reduced enamel crystallinity more than dentin, altered protein/mineral ratios, and these changes likely contribute to radiation caries formation.

Abstract

Radiation caries is a complication of radiotherapy characterized by enamel erosion and dentin exposure. The mechanisms of characteristic radiation caries formation are not well-understood. The aim of this study was to evaluate the direct radiation-induced effects on dental hard tissue and investigate their role in the formation of radiation caries.Sixty non-carious third molars were divided into three groups (n = 20), which would be exposed to 0 Gy, 30 Gy, and 60 Gy radiation, respectively. After radiation, microhardness and elastic modulus were measured at four depths by means of a Vickers microhardness tester and atomic force microscopy (AFM). The microstructure was observed by scanning electron microscopy (SEM). X-ray diffraction and Raman microspectroscopy were used to determine crystal properties and protein/mineral (2931/960 cm- 1) ratios.A statistically significant decrease in microhardness and elastic modulus values 50 μm from the dentino-enamel junction (DEJ) in enamel was revealed in the 30-Gy and 60-Gy groups. With the increasing dose, destruction of interprismatic substance and fissures at the DEJ-adjacent region were found. A greater reduction of crystallinity was revealed in enamel compared with dentin. Raman spectroscopic analysis showed a slight increase of the protein/mineral ratio for enamel following accumulated radiation, while the protein/mineral ratio for dentin was decreased.Radiation could directly alter the mechanical properties, micro-morphology, crystal properties, and chemical composition of dental hard tissue. The early destruction of DEJ-adjacent enamel, combined with decreased crystallinity of enamel under radiation exposure, may be related to the formation of characteristic radiation caries.