[The cellular and molecular bases of "tooth framing"]

Progress in molecular biology in recent years has enormously increased interest in tooth generation. The enamel knot has been discovered, in consequence. This is a transient structure acting as molecular signaling center, responsible for controlling cusp formation, stimulating growth of surrounding epithelium, and generating new knots or their disappearance through apoptosis. Both tooth development and enamel knots are regulated by a cascade of gene activity where Fgf4, Shh, BMP4, Lef1 and p21 are the prime movers of the processes. Homeobox genes (Msx, Dlx) are the orchestrators of the framing and a series of proteins (adhesion molecules, extracellular matrix components) are the executors of "tooth framing". An important concept has emerged from developmental biology through the identification of the basic mechanisms involved in tooth development: the molecular basis of structure framing shares common rules. Thus similar genetic programs are involved in body structure generation (limb bud, tooth, branching morphogenesis). A deeper understanding of developmental rules regulating tooth formation will make it possible in the near future: a) to modify in vivo homeobox gene expression and restore tooth generation hampered by tooth agenesia due to homeobox gene deregulation; b) to induce complete tooth formation, in case of tooth loss due to trauma or diseases, through implantation in the patient's oral cavity of a synthetic ball containing morphogens and growth factors to stimulate, in the right spatio-temporal sequence, the entire tooth genetic cascade. These concepts will certainly enforce cultural and practical interaction between biology and dentistry.