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 tooth development.
Currently, a number of animal models are being investigated to achieve a better understanding of tooth regeneration. These animal models however, provide limited understanding of the entire regenerative process because of certain odontogenic dissimilarities between humans and the models. Sources for adult stem cells are being investigated as they could provide an important channel for tooth regeneration, and or replacement in teeth bioengineering. While mesenchymal stem cells and epithelial stem cells have been discovered, they do not provide an adequate source for stem cell research and tooth bioengineering. Derivation of induced pluripotent (iPS) stem cells from differentiated adult cells provides a sufficient source for investigation, and they appear to be the most viable source for reprogramming. Before successful reprograming can be achieved, the complete intricate interactions between the epithelium and mesenchyme must be fully elucidated. This paper presents the currently known features of odonotgenesis at the molecular level, and the current research on tooth regenerative capacity by use of the known signaling interactions.
Before discussing tissue bioengineering...