Scanning electron microscopy of the extracellular matrices of rat molar tooth germs in organ culture in vitro.

Second upper molars from 3-day postnatal rats were cultured for 2 weeks and compared with in-vivo specimens from 7-day postnatal rats. Several preparatory techniques were applied to expose the extracellular matrices, the three-dimensional structure of which were examined by SEM. The combination of phosphate-buffered saline and ultrasonics as preparation for the observation of the enamel, hypochlorite treatment to study the predentine, the freeze-fracture technique for the dentinal tubules and oxygen-plasma-ashing for the mineralization front of dentine gave best results. Enamel formed in vitro was prismatic similar to in vivo. The fissures were devoid of enamel and the enamel-free areas at the cusp tips were larger than in vivo. In the cervical area in vitro, the enamel stopped abruptly instead of gradually decreasing. The predentine and the dentine were normal in structure.