Background. Radiotherapy, applied to the head and neck region, can cause radiation side effects such as reduction of saliva and radiation caries. The aim of this study was to perform an in vitro assessment of the effects of radiation therapy on the morphological, mechanical, and chemical properties of primary and permanent teeth. Methods. 92 extracted human teeth (46 impacted wisdom teeth, 46-primary molar teeth) were used. The teeth were divided into two directions: the mesiodistal direction

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... d the vestibulolingual direction. The vestibular sections were used for vickers analysis, and lingual sections were used for Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) analysis. The teeth in the experimental group were fixed to wax models. Each model had an equal number of teeth (n=7). The doses were applied to the teeth for 6 weeks; 5 week days and 2Gy daily. After the radiotherapy conducted weekly, a wax model was taken from radiation reception. Along with elemental contents (Ca, P, Na, Mg, P) of the teeth, enamel and dentin microhardness were evaluated, and SEM analyzes were performed on 8 teeth. These teeth were compared with the other non-irradiated sections. Results. Radiation caused a decrease in microhardness of enamel and dentin(p<0.05). In elemental analysis by ICP-OES, it was observed that there were decreases in all doses, while the highest decrease was in 60Gy dose(p<0.01). In the experimental groups, amorphous structures were encountered in SEM images. Conclusions. Radiation has negative effects on the teeth structure and additional studies are needed in this regard. This study indicates that radiotherapy patients are at a higher risk for dental caries