2019 Volume 43 Issue 3 Pages 140-152
Previously, we have elucidated the role of insulin-like growth factor-I （IGF-I） during the early stages of tooth root formation in mandibular first molars of 5-day-old mice. We reported that IGF-I stimulates the mitotic activity in the outer enamel epithelium of the Hertwig's epithelial root sheath （HERS）, resulting in the elongation of the root. In the present study, we used mandibular first molars from 20-day-old mice in order to further elucidate the role of IGF-I during the later stages of tooth root formation. The control explants showed normal development of the HERS, similar to that in vivo. But the explants treated with 100 ng/ml of IGF-I showed diminished cell proliferation in the inner and outer layers of the HERS. In addition, obvious disintegration of the root sheath along with the appearance of cellular cementogenesis was noted. It was considered that IGF-I signaling accelerated the changing rate, from the maintenance of the length via cell proliferation to the disintegration of the HERS layer, eventually facilitating the differentiation of cementoblasts and cellular cementogenesis. These findings indicated that IGF-I is one of the important regulatory factors throughout root formation.
