The presence of fenestrated capillaries in the papillary layer of the enamel organ

The capillary network of the papillary layer of the enamel organ was studied with the electron microscope. Mandibular incisor teeth of ten‐day old Swiss albino mice were fixed in formaldehyde‐glutaraldehyde, postfixed in osmium tetroxide and prestained with 0.5% uranyl acetate prior to being embedded in Epon. Examination of ultrathin sections revealed the presence of fenestrations approximately 500 Å to 700 Å in diameter within the most attenuated regions of the capillary walls. In most instances the fenestrations appeared to be closed by diaphragms usually consisting of a thin membrane with a thicker centrally located button of electron opaque material. The presence of fenestrated capillaries within the papillary region of the enamel organ lends further support to the concept that papillary cells are engaged in transport functions during the maturation of enamel.