Potential contribution of dental pulp stem cells to pulp and dentin repair in response to tooth injury: A preliminary study

We investigated the capacity of dental pulp stem cells to induce the formation of a reparative dentin-like structure upon implantation within the pulp, after a surgical exposure. For this purpose, we established cell lines displaying stem cells properties from molar dental pulp of mouse embryos. Among these cells, « A4 » cell line maintains a stable mesoblastic phenotype and never differentiates spontaneously under long-term standard culture conditions. This clone was implanted in the rat first maxillary molar (a model used in our laboratory), to evaluate whether these pulpderived precursor cells are able to synthesize, in vivo, a dentin-like structure. When the surgery alone was performed, after an early inflammatory process, a heterogeneous matrix, characterized by large gaps and pulp remnants, gradually filled the mesial part of pulp chamber in 30 days. This non-mineralized permeable structure is unable to resist a bacterial re-infection. When clone A4 was implanted into a rat molar pulp lesion, after one month, a dense mineralized dentin-like structure was formed in the implantation site, filling homogeneously the mesial part of pulp chamber. Agarose beads were implanted alone but also were used as cell carrier. Preliminary experiments using A4 progenitors carried out by alginate beads suggest 1) that dental pulp stem cells induce the formation of robust reparative dentin and therefore constitute useful tool in pulp therapies, and 2) that alginate is a suitable carrier for cell implantation. Despite surgical trauma and stem cells implantation, reparative processes do not affect the structure and vitality of residual pulp in central and distal parts of pulp chamber. Future prospects will be focused to determine whether implanted progenitor cells are directly involved in the formation of reparative dentin or whether they induce recruitment and differentiation of host progenitor cells.