Molecular and engineering approaches to regenerate and repair teeth in mammals

Continuous replacement of teeth throughout the lifespan of an individual is possibly basal for most of the vertebrates including fish and reptiles; however, mammals generally have a limited capacity of tooth renewal. The ability to induce cellular differentiation in adults to replace lost or damaged cells in mammals, or to tissue-engineer organs in vitro, has hence become one of the major goals of regenerative medicine. In this article, we will revisit some of the important signals and tissue interactions that regulate mammalian tooth development, and will offer a synopsis of the latest progress in tooth regeneration and repair via molecular and engineering approaches. It is hoped that this article will not only offer an overview of recent technologies in tooth regeneration and repair but will also stimulate more interdisciplinary research in this field to turn the pursuit of tooth regeneration and repair into practical reality.

Three-dimensional analysis of the early development of the dentition

Tooth development has attracted the attention of researchers since the 19th century. It became obvious even then that morphogenesis could not fully be appreciated from two-dimensional histological sections. Therefore, methods of three-dimensional (3D) reconstructions were employed to visualize the surface morphology of developing structures and to help appreciate the complexity of early tooth morphogenesis. The present review surveys the data provided by computer-aided 3D analyses to update classical knowledge of early odontogenesis in the laboratory mouse and in humans. 3D reconstructions have demonstrated that odontogenesis in the early stages is a complex process which also includes the development of rudimentary odontogenic structures with different fates. Their developmental, evolutionary, and pathological aspects are discussed. The combination of in situ hybridization and 3D reconstruction have demonstrated the temporo-spatial dynamics of the signalling centres that reflect transient existence of rudimentary tooth primordia at loci where teeth were present in ancestors. The rudiments can rescue their suppressed development and revitalize, and then their subsequent autonomous development can give rise to oral pathologies. This shows that tooth-forming potential in mammals can be greater than that observed from their functional dentitions. From this perspective, the mouse rudimentary tooth primordia represent a natural model to test possibilities of tooth regeneration.