The original fetuses and newborn analysed and described previously and 2 additional newborn animals were examined in the present study. Because of the complexity of the morphology of some of the fused teeth, we decided to undertake their 3-D reconstruction using Mouse Atlas Project reconstruction methods. Intermittent transverse serial sections through the maxillary region of a p53-deficient exencephalic newborn mouse with an example of fused maxillary incisor teeth associated with a dens in dente . Both the 'crown' of the latter and the labial aspect of the crown of the fused teeth are covered by a very thin layer of preameloblast. A thin layer of dentine is present with an artefactual space separating it from the overlying layer of preameloblast.
Definitive enamel has yet to form.
Both series stained with haematoxylin and eosin. This software was used to define the volumes occupied by the dentine and enamel for visualisation using the commercial 3-D rendering software AVS . 3-D reconstructions of the fused teeth demonstrated that they were all of the fusio subtotalis variety. It is believed that the presence of dens in dente within fused maxillary incisor teeth has only once been reported in mice, and the association between fused maxillary incisor teeth and a median supernumerary incisor tooth has not previously been reported in this species. This is not shown in these reconstructions.