Tooth patterning and evolution.

Teeth are a good system for studying development and evolution. Tooth development is largely independent of the rest of the body and teeth can be grown in culture to attain almost normal morphology. Their development is not affected by the patterns of movement or sensorial perception in the embryo. Teeth are hard and easily preserved. Thus, there is plenty of easily accessible information about the patterns of morphological variation occurring between and within species. This review summarises recent work and describes how tooth development can be understood as the coupling between a reaction-diffusion system and differential growth produced by diffusible growth factors: which growth factors are involved, how they affect each other's expression and how they affect the spatial patterns of proliferation that lead to final morphology. There are some aspects of tooth development, however, that do not conform to some common assumptions in many reaction-diffusion models. Those are discussed here since they provide clues about how reaction-diffusion systems may work in actual developmental systems. Mathematical models implementing what we know about tooth development are discussed.