A Model Simulating Tooth Morphogenesis without Morphogens

A graphic two-dimensional model, run on a computer, is used to describe the development of tooth shape. The model starts with two cells on each side of a basement membrane and grows to 1000 cells. Active forces are created by random growth of one cell layer (the internal dental epithelium) and a constant preferred direction of growth of the other layer (the surface of the dental papilla) which has been observed. The growth forces pushing cells apart are constrained by forces known to exist: (i) the attachment of cells to the basement membrane; (ii) the development of hydrostatic pressure due to proteoglycans in the stellate reticulum of the enamel organ; and (iii) the growth of the dental papilla. The two cell layers in the model are growing at different speeds over the basement membrane. Their mechanical interaction causes them to fold into shapes determined by the forces. The effects on tooth shape of different forces are plotted graphically. Occasionally, the model developed two entirely different shapes under identical conditions, but in most cases the shapes were consistent for every run of the model. Many observations of tooth development and results of experimental embryology can be explained by the ways in which the modelled cells were observed to behave. It is possible that the model could be applied to the development and/or patterning of other embryonic shapes where a basement membrane separates layers of cells with different growth rates.