Research has shown that tooth development is regulated by interactions of the epithelial and mesenchymal tissues. The tissues interact reciprocally, sending signals to each other. These signals are most often small proteins that are secreted by one tissue and received by another. The cells interpretation of a received signals then determines its response, growth, gene expression or even cell death. It is obvious that there are subtle differences of these signals during development of different teeth. Similar signals and responses are used during development of many organs.