Proliferative changes in the tooth germ and their effects on dental growth patterns as observed in mice following prenatal exposure to X-rays

The effects of acute exposure to X-rays on dental development were ascertained in albino mice with the first molar tooth being used as a test parameter. Irradiation was carried out during the period between day 11 and day 15 after fertilisation using doses in the range from 0.5 to 3.0 Gy. Acute proliferative changes were evaluated by means of histoautoradiography on the basis of the amounts of 3H-thymidine found in the tooth germ's DNA. The latter were determined from the density of labelled cells as a special test variable. In order to ascertain the more remote influences of irradiation, morphometric measurements were additionally carried out in microsections of the fully developed teeth. The maxillary and mandibular molars and their respective tooth germs showed similar responses to radiation exposure. The findings revealed gave indications of radiation-induced retardations or temporary interruptions of the cell cycle, partial synchronisation for overreacting cells and eventual reversion to normal. Those deviations in the proliferative growth patterns of tooth germ had as a result that the mature teeth tended to be smaller in size. The reductions in both tooth diameter and thickness of enamel were seen to be phase-dependent. The fact that the influences were more evident after late radiation exposure (towards day 15) was attributed to an age-related deterioration of regenerative accomodation processes and their inhibition by the formation of hard matter from day 16 after fertilisation onwards. (orig./MG)