Abstract
The purpose of this study was to investigate the effect of radiation on the growth and development of tooth germs, particularly concerning the differences in the effect caused by the variation of the dose and time of the irradiation.
A 6MV X-ray was irradiated onto the abdomen of pregnant mice.
Under anesthesia, fetuses were enucleated from the maternal uterus, and their tooth germs were examined histologically and the shapes and form of the tooth germs were analyzed by computer assisted 3-D reconstruction.
The following results were obtained:
1 ) There was no surviving fetus in the pregnant mice groups 3,4, and 5 Gy irradiated on the 9th and the 10th gestational days, and 5 Gy on the 11 th gestational day.
2 ) The body weight of the fetuses irradiated on the same gestational day decreased with an increase of exposure.
3 ) The tooth germs of the groups which were irradiated in the early period of development (during the 9th day to 13th gestational day) exhibited growth retardation and undersizing.
4 ) The tooth germs of the groups which were irradiated in the early period of development also decreased in the enamel organ volume and dentin surface area.
5 ) In the groups irradiated 4 and 5 Gy, the enamel organ volume decreased more in the tooth germs of the fetuses irradiated earlier, while in the irradiated groups 1,2, and 3 Gy, there was no relationship found between enamel organ volume and the gestational day.
6 ) Considering the ratio between enamel organ volume to dentin surface area, and the ratio between enamel organ volume or dentin surface area to the weight of the fetus, it appeared in the irradiated groups that the dentin surface area decresed more than the enamel organ volume did.
7 ) The tooth germs of the group 5 Gy irradiated on the 12th gestational day did not show any histological changes immediately after irradiation. Meanwhile, the shapes of the tooth germs on the 14th day corresponded to the 13th gestational day.
The results suggest that when the tooth germs were irradiated in the early period of development, they suffered from retardation of the growth and undersizing, and that the effect corresponded to the dose of irradiation. It also shows that the odontblasts and the mesenchymal cells which will differentiate into the odontblasts are affected more than the cells of enamel organ.
