Aspects of cell proliferation kinetics of the inner dental epithelium during mouse molar and incisor morphogenesis: a reappraisal of the role of the enamel knot area

First lower E-14 and E-16 mouse molars and E-13 lower incisors were culture d in vitro and either sequentially or continuously labelled with BrdU (5-br omo-2'-deoxyuridine). The behaviour of the non-cycling inner dental epithel ial cells emerging from the enamel knot area of the molars was analysed by 3D (three dimensional) reconstructions of serial sections. These cells, as well as slow cycling cells underwent a coordinated temporo-spatial patterni ng leading to their patchy segregation at the tips of the forming cusps. In incisors (in vitro and in vivo), non-cycling cells were also present in th e inner dental epithelium of the enamel knot area. However, these cells wer e not redistributed during incisor morphogenesis. These non-dividing inner dental epithelium cells of the enamel knot area which are either redistribu ted or not according to the tooth type specific morphogenesis might represe nt the organizers of morphogenetic units (OMU), the cusps.