The Different Types of Teeth of Mammals

In mammals teeth develop as distinct organs. Some organs such as hair and certain glands share similarities with tooth organogenesis in their morphological and molecular features of development, but not their regenerative abilities. Dentition, by definition, refers to characteristics of a set of teeth including type, arrangement, shape, and number. During their evolutionary course, mammals have developed a reduced ability for tooth regeneration, but on the other hand mammalian teeth have developed many variations in size and shape. Mammalian dentition can be divided into four tooth types; incisor, canine, pre-molar (bicuspid), and molar teeth. Molar teeth specifically are the most diversely shaped teeth of the four types.

Although teeth can develop from either endoderm or mesoderm, in mammals neural crest and ectodermal tissues produce ectodermal appendages, which later grow as teeth (Smith, 2003; Soukup et al., 2008). Cell-cell signaling and cell differentiation between the ectoderm and mesenchyme cells regulate tooth morphogenesis. Many paracrine signal molecules that we know are involved, and mediate communication during tooth development. Most of these signals are from the Hedgehog (Hh), Ectodysplasin (Eda), transforming growth factor ß (TGFß), Wnt, Bone morphogenic protein (Bmp) and fibroblast growth factor (FGF) conserved signaling groups (Jernvall and Thesleff, 2000). These conserved signaling families also play significant roles in regulating many other aspects of embryonic development. They not only regulate communication between germ layers, but also within each germ layer. The variation in mammalian dentition relies on these cell signals to regulate differentiation, thus they are present from start to finish of too...

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Even after reprogramming the cells for tooth development, the techniques used in this process will have to take into account the natural environment of the cells. Based on the current understanding of tooth development that we have seen above, it is clear that the techniques used in tooth bioengineering will be of significantly higher complexity than that of reprogramming pancreatic cells, and this would have to be done inside the oral cavity.

A clear understanding of the mechanisms involved in normal tooth development is required to develop methods of programming tooth regeneration in humans. The stem cells in mammalian teeth might not be a good source for bioengineering due to their limited supply and problematic collection methods. Non-dental stem cells such as iPSCs is thus far shown to be one of the most promising tooth bioengineering avenues to explore.