Tissue interactions in development of teeth and related ectodermal derivatives.

A number of traditional techniques have been used to examine epithelial-mesenchymal interactions; they remain to this day the only means to examine the problems of tissue interactions. Problems at the tissue level of organization require that the approaches to these problems ask questions and use techniques that address the issues of tissue organization and cellular morphology in the context of three-dimensional organization. Manipulating the embryo is exactly that--manipulating a three-dimensional organized organism that must express its differentiated functional organs and organ systems. When the parallel and correlative studies of cell biological function achieve new insights, they will have to be tested in terms of the cellular response at the tissue level of organization.