Effects of ionizing radiation on mechanical proprieties of restorative materials and enamel in upper molars: an in-vitro study

Introduction
Radiotherapy is one of the most commonly used treatment modalities for head and neck cancer patients, but the effects of ionizing radiation on restorative tooth materials and enamel are largely unknown. This study aimed to assess the effects of ionizing radiation on mechanical properties of restorative materials and enamel in upper molars.

Material and methods
A total of 60 extracted human molar teeth (40 with minor occlusal caries and 20 non-carious) were used in this study. Teeth were randomly divided into three groups, including group 1 (control group, samples received no restorative materials), group 2 (teeth were restored in-vitro with glass ionomer cement), and group 3 (teeth were restored in-vitro with flowable resin composite). Each group was divided into two sub-groups: those irradiated with a single dose of 70 Gy and those non-irradiated. Rockwell hardness tests and radiodensity measurements on Hounsfield scale were applied to the teeth before and after irradiation. A compression test was done at the end of the experiment.

Results
Radiation therapy caused significant reductions in the surface hardness in the two restorative groups (p < 0.001). Hounsfield units in the flowable resin composite group markedly decreased after radiation (p < 0.001). However, no significant effects in compressive strength were observed in any group treated with radiation.

Conclusions
These results showed that radiation has negative effects on the mechanical properties of the teeth. The surface hardness was significantly depressed by ionizing radiation. Since the radiodensity in Hounsfield scale was markedly diminished in the flowable resin composite group, glass ionomer cement could be a better alternative for cementation in teeth subjected to radiation.