Pregnant mice were treated with a single intraperitoneal injection of 10,000 I.U. vitamin A on day 8, 9, 10, 11 and 12 of pregnancy respectively. Offsprings were examined on day 18. In the results, cleft palate, malformations of the digit and pathologic changes in the tooth were the notable malformations observed. The author of the present paper especially paid attention to pathologic changes in teeth and their morphogenetic study was planned. Among various kinds of pathological changes observed in the tooth germs, the most remarkable one was hemorrhage in the dental papilla and the enamel organ. No differences were seen between the germs of the incisor and molar. Severe hemorrhagic changes were more prevalent in the fetus treated in the early stage of development than in the later stage. Disordered arrangement and partial necrosis due to hemorrhage were observed not only in the odontoblast layer but also in the layers of inner or outer dental epethelium. In severe cases, a wavy pattern was present in the predentine, and said pattern was caused by disarrangement of odontoblasts and ameloblasts. Such disarrangement seemed to be due to massive hemorrhage extending from the dental papilla into the enamel organ. The findings observed in the present study would suggest that the hypoplastic dental development in these experimental cases may originate from the above pathological changes in the odontoblast and ameloblast layer. Further, it may be concluded that the disturbed morphogenesis of teeth was due to hemorrhage in the tooth germ of the mouse fetus, and such hemorrhage was caused by hypervitaminosis A from day 8 to 12 of pregnancy.
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