A chain of reciprocal interactions between the epithelial and mesenchymal tissues regulates both morphogenesis and cell differentiation in the developing tooth. The very early interactions lead to budding of the oral epithelium and to the characteristic condensation of the neural crest-derived mesenchymal cells around the epithelial bud. During the bell stage of morphogenesis, the mesenchymal cells which are in contact with the dental epithelium differentiate into odontoblasts. In this reveiw article we summarize the results of our descriptive and experimental studies, which indicate that differentiation of the dental mesenchymal cells into odontoblasts, as well the condensation of dental mesenchymal cells at the bud stage, are regulated by interactions between the cell surface and the extracellular matrix. Transfilter studies where the dental epithelium and mesenchyme were cultured on opposite sides of Nuclepore filters, led to the hypothesis that the differentiation of dental mesenchymal cells into odontoblasts is triggered by interactions between the cell surface and the epithelial basement membrane matrix. Immunohistochemical localization of various matrix molecules showed that the matrix glycoproteins fibronectin and tenascin are accumulated in the dental basement membrane at the time of odontoblast differentiation. Fibronectin and tenascin are known to interact with each other, with other matrix molecules as well as with the cell surface, and also to influence cell shape. We suggest that fibronectin and tenascin are involved in the cell-matrix interaction which leads to the polarization and differentiation of odontoblasts.(ABSTRACT TRUNCATED AT 250 WORDS)