Experimental formation of dentin-like structure in the root canal implant model using cryopreserved swine dental pulp progenitor cells

Objectives: The purpose of the present study was to present histological and immunohistochemical evidence demonstrating the regenerative capacity of swine dental pulp stem cells (S-DPSCs) seeded on organic or synthetic scaffolds and implanted as hybrid root implants in the jaw bone of mini pigs.Methods: Immature permanent incisor teeth and unerupted premolars at the early root-forming stage were extracted from three seven-month-old mini-pigs and mesenchymal stem / progenitor cells were isolated from dental pulp. Cells were cryopreserved in liquid nitrogen. Σeeth were processed for histological analysis in serial sections. Relationships between the anatomical zones of dental mesenchyme at the root apex were morphologically evaluated in hematoxylin-eosin and immunohistochemically stained for Tenascin-C and Syndecan-1 sections. A year later, new permanent incisor and premolar teeth were extracted, pulp tissue was removed and pieces of root canals of the extracted teeth, containing collagen or PLGA scaffolds seeded with the autologous cryopreserved DPSCs, were implanted into the fresh post-extraction socket of the mini pig jaw. The resulting constructs were harvested after 6 and 10 weeks and evaluated by histological and mmunohistochemical analyses.Results: Stem / progenitor cells isolated either from dental pulp or apical papilla tissue were found to be positive for CD90, CD105 and CD146 and negative for STRO-1 CD29 & CD31. Syndecan-1 immunostaining was detected in the odontoblastic layer along the newly deposited root dentine and the dental pulp around the capillaries. Tenascin-C was intensely expressed in the subodontoblastic cell region along the newly deposited root dentine and the whole dental pulp parenchyme. Apical papilla and dental follicle were negative for both antibodies. 6 weeks postoperatively, the central canal space of the root implants showed degrading scaffold material. New extracellular matrix had been deposited in a polar predentin-like pattern on the canal dentinal walls by cuboidal non-polarized cells. 10 weeks postoperatively, newly formed organic matrix had been consistently deposited on the canal walls. The presence of a continuous layer of polarized cells showing typical columnar morphology, adjacent to the newly deposited organic matrix was evident.Conclusions: The interactions of S-DPSCs with the dentin matrix of roots implanted in the jawbone of mini pigs constitute a model to study in vivo organization and differentiation potential of DPSCs. Expression patterns of the molecules Tenascin and Syndecan are very different between dental pulp and apical papilla tissues. Furthermore, it seems evident that cell surface markers are not able to identify by flow cytometry, individual dental stem / progenitor cell populations isolated from developmentally different areas