Wednesday, 15 November 2017

The Diversity of Pulp Stem Cells, Tools for Regenerative Biodentistry


Since the publication of Spallanzani, it is known that following surgical amputation, the tail of the urodele amphibians Xenopus tadpole regenerates. Restoration of tails, legs and jaws also occurs in the salamander after surgical removal. At the same period, Trembly split hydra heads and obtained multiheaded individuals. By bisecting a hydra, two complete animals were produced. During many years, a gap persisted between the biological regenerative capacities and what was requested for surgical therapies. This gap was gradually reduced, and now nearly disappeared. Successive steps highlight the fundaments of regenerative biodentistry. Implantations of stem cells and surgical approaches in dentistry are derived from epithelio-mesenchymal assembly of embryological tissues. After reactivation of the concepts ahead of clinical applications, new treatments guiding organ repair and regeneration in mammals pave the way for biodentistry improvements. Indeed, applied to the field of human therapies the replacement of lost teeth by tissueengineered dental recombinants appears as a fascinating goal. 

The initially aim of dental tissue engineering was to generate a whole tooth, or within some limits took into consideration, to concentrate on the regeneration of a missing part. The aim of dental tissue engineering may been limited to enamel repair, but this is still at an experimental stage. Or a more realistic objective was to heal the dental pulp, and consequently to provide a contribution to dentin mineralization as a substitute to endodontic therapy. Restorative approaches of root canal treated tooth have relatively limited long-term survival and many failures are associated to diverse complications such as transversal or longitudinal fissures followed by subsequent fractures, and/or chronic periapical inflammation. Substitutive therapies to endodontic treatments have been suggested and innovative strategies have been envisioned, including metallic implants or bridges. However, during the last decades, advances in the understanding of tooth development, as well as stem cell biology permit to consider the biological replacement of lost dental tissues and provide the foundation of novel opportunities in dental tissue engineering. Developing dental substitutes appear not only as a fascinating goal in restorative dentistry, but raises also the question of technical feasibility. It is clear that many open questions take origin from a series of interrogations and the answers that are given are still confusing. 

What is exactly our goal? Are we willing to create or recreate a whole tooth? Are we willing to regenerate only a small part of dental tissues? Our aim may be limited to the healing and regeneration of a dental pulp? But will it be possible to use the newly formed pulp as a support for pulp mineralization, playing a role as a potential substitute for endodontic treatment? Each attempt to provide an efficient clinical answer implicates another strategy. Alternatively, it seems sometimes mandatory to evaluate the value of another method, another technic or to test another biomaterial. Consequently, any improvement needs firstly the identification of the question to be answered, and afterward the development of adapted cellular or biological materials. The present approaches imply stem cells, scaffolds, structural and signaling molecules, transcription and growth factors. In this review we concentrate exclusively on the current knowledge related to pulp stem cells and we discuss their potential functions and implications in regenerative dentistry. 

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