Pulp healing and regeneration: more questions than answers.

Differences between pulp repair and regeneration guide different strategic options. After mild carious dentin lesions, odontoblasts and Hoehl's cells are implicated in the formation of reactionary dentin. Reparative dentin formation and/or pulp regeneration after partial degradation is under the control of pulp progenitors. A series of questions arise from recent researches on tissue engineering. In this series of questions, we compare the therapeutic potential of pluripotent embryonic and adult stem cells, both being used in cell-based dental therapies. Crucial questions arise on the origin of stem cells and the localization of niches of progenitors in adult teeth. Circulating progenitor cells may also be candidate for promoting pulp regeneration. Then, we focus on strategies allowing efficient progenitors recruitment. Along this line, we compare the potential of embryonic stem cells versus adult stem cells. Re-programming adult pulp cells to become induced pluripotent stem cells constitute another option. Genes, transcription factors and growth factors may be used to stimulate the differentiation cascade. Extracellular matrix molecules or some bioactive specific domains after enzymatic cleavage may also contribute to the formation of an artificial pulp and ultimately to its mineralization.