Figure 2. Apoptosis in 3D reconstructions of the dental epithelium in the cheek region of the mandible at ED 15.5, 16.5, and 17.5. Apoptosis presented by apoptotic cells and bodies (black dots) is increased in Ta mice. It is distributed mesio-distally to a similar extent in all Ta morphotypes, but it affects different structures according to the specific tooth pattern (compare with Fig. 1). The mesenchymal face of the dental and adjacent oral epithelium is shown from an aerial view in wild-type (WT) controls and in subtypes Ia and Ib of Ta dentition. The pictures have been unified to show the right-side dentition. WT and Ta specimens of similar weight (Peterka et al., 2002) were selected for comparison on each of the embryonic days. Consequently, inter- and intra-litter variability in the length of the dental epithelium was minimalized (also see Figs. 3, 4). Various stages of tooth development are represented: The WT mice show the cap stage of M₁ at ED 15.5, the cap-bell transition of M₁ and the late bud/early cap of M₂ at ED 16.5, the bell of M₁, and the late cap of M₂ at ED 17.5. In Ta subtypes Ia and Ib, the cap stage of T₁ and the late bud/early cap of T₂ occurred at ED 15.5, the early bell of T₁ and the cap of T₂ at ED 16.5, and the bell of T₁ and T₂ and the bud of T₃ at ED 17.5. "mer" = mesial epithelial ridge (the epithelial ridge extending mesially from the primordium of the most mesial cheek tooth). Arrow = apoptosis in the pEK.