Comparison of growth and cell proliferation kinetics during mouse molar odontogenesis in vivo and in vitro.

The growth of embryonic first lower mouse molars in vitro was slow and reduced in comparison with in vivo development: the volume of teeth removed on day 15 and 16 of gestation and cultured for 6 days did not exceed the volume reached at day 18 in vivo. The volume of teeth removed on day 17 and 18 and cultured for 6 days either remained constant or decreased. The appearance of post-mitotic odontoblasts and ameloblasts was delayed in vitro. This behaviour might be correlated with a lengthening of the cell cycle (Tc). In vitro, the average durations of Tc (established by the percentage labelled mitoses technique) were 17.4-20.2 hr and 19.1-19.4 hr for pre-odontoblasts and pre-ameloblasts respectively. In vivo, the corresponding Tc values were 13.9 hr and 13.5 hr. The coordination of mitotic activities of pre-odontoblasts and pre-ameloblasts existing in vivo was maintained in vitro, and therefore seemed to require intra-dental control mechanisms. Non-specific extra-dental serum factors may affect the duration of Tc.