AbstractThis study was undertaken to investigate the morphological relationship between jaw malformations and developmental disorders of tooth germs in mouse fetuses following maternal hypervitaminosis A.Pregnant Slc‐ICR mice were treated with a single ip injection of 20000IU vitamin A on day 8, 9 or 10 of pregnancy (VP=0). On days 14–18, they were sacrificed, and the fetuses were examined for jaw and tooth germ anomalies with bone‐stained specimens and histological sections.In the group treated on day 8, mandibles were involved with severe reductional deformities. In the fetuses with defect of the rear portion of the mandibular corpus and ramus, a pair of incisor‐like heterotopic tooth germs were observed behind the incisors. These abnormal tooth germs had osteodentine in their pulps, and no cusp was formed. No tooth germ with molar structure was detected. In the fetuses with less severely deformed jaws, hypoplasia and disarrangement of molars were characteristic. Significant changes on days 14–15 were irregular and excessive epithelial invaginations from the molar dental laminae.The tooth anomalies induced by maternal hypervitaminosis A such as incisor‐like heterotopic tooth germs and hypoplastic and disarranged molar germs may have resulted from spatial derangement of odontogenic mesenchyme due to a deficit of the embryonic facial