There are two strategies for pulp regeneration at present: cell transplantation and homing. The former method is based on cells by transplanting exogenous stem cells onto scaffolds [4]. Root fragment models for pulp regeneration have been discussed in many studies, which show that pulp-like tissues can be produced in vivo by transplantation of dental pulp or other stem cells into tooth slices or fragments [5, 6, 7, 8]. Previous studies have selected human single premolar fragments as carriers for implantation into animals. In our study, we chose the rat incisor root as a carrier to avoid immune rejection of the experimental animals to the greatest extent. Rat bone marrow mesenchymal stem cells (rBMSCs) combined with collagen membrane scaffolds were implanted into rat incisor teeth fragments, and new tissue filling the pulp cavity was observed in the root segment of rat incisor teeth. H&E and immunohistochemical staining showed the appearance of odontoblast-like cells and neovascularization.
iRoot BP as a new nano-bioceramic material is a recently developed bioceramic-based endodontic cement with improved performance compared with MTA [9]. Its main components include calcium trisilicate, calcium disilicate, calcium phosphate, tantalum oxide, and zirconi [10]. Compared with MTA, iRoot BP plus has the same cytotoxicity, apical closure, and antimicrobial activity [11]. In addition, it overcomes the shortcomings of MTA. Therefore, iRoot BP plus has recently been considered as an alternative to MTA.
Several studies have shown that iRoot BP can be used for direct pulp capping without pulp inflammation [12, 10]. However, there is no report on its application to pulp regeneration. In our study, one side of the root segment was closed by iRoot BP, which showed that iRoot BP had good biocompatibility with new dental pulp tissues, and odontoblast-like cells and neovascularization were seen in the new tissues.
Angiogenesis is a crucial cellular morphogenesis process through which new blood vessels grow from existing blood vessels, penetrate the extracellular matrix, and generate new blood vessels to meet local metabolic needs [13, 14]. Promoting angiogenesis has been emphasized as a key strategy in regenerative medicine, which stimulates the repair of damaged tissues, such as bone, cartilage, muscles, and nerves, by providing effective nutrition and oxygen [ 15, 16]. Angiogenesis is thought to be an important factor in pulp regeneration, because only blood vessels are generated in the canal space, leading to long-term stability of the newly formed tissues [5]. In the iRoot BP + rBMSC group, iRoot BP slowed absorption of the collagen, but neovascularization near BP1/3 was significantly more than that at other sites, indicating that iRoot bp significantly promotes the regeneration of blood vessels.
Markers such as DMP1, DSPP, ALP, OCN, and RUNX2 are commonly used to evaluate odontogenic differentiation of stem cells from different sources [17, 18]. In our study, we chose DSPP as a marker of odontogenic differentiation. VEGF plays an important role in angiogenesis by promoting endothelial cell proliferation, increasing vascular permeability, and changing the biological effects of the extracellular matrix [19]. In this study, PGP9.5 protein was selected to reflect the nervous system, because it is a specific marker of neurons and nerve fibers, which reflects the degree of damage and repair of neurons and nerve fibers [20]. IHC of DSPP, VEGF, and PGP9.5 showed that iRoot BP promoted the differentiation of mesenchymal stem cells into dentin and generated pulp-like tissue with blood vessels and nerves.