Regenerative endodontics has been described as a paradigm shift in dentistry, despite its current limitation to immature teeth and reparative rather than regenerative outcomes. Cell-free treatments are favored because of regulatory issues. However, the recruitment of host-derived stem cells to the desired site remains challenging. We investigated whether dental pulp-derived exosomes, which are extracellular vesicles that contain proteins, lipids, RNA, and DNA and thus mirror their parental cells, may be used for this purpose. The use of exosomes may present appreciable advantages over the direct use of transplanted stem cells due to a higher safety profile, easier isolation, preservation, and handling. Here we harvested exosomes from a cultured third-molar pulp cell and assessed them by transmission electron microscopy and Western blotting. Human mesenchymal stem cells (MSCs) were exposed to these exosomes to assess exosome uptake, cell migration, and proliferation. In addition, a fibrin gel (i.e., a diluted fibrin sealant), was assessed as a delivery system for the exosomes. Our results show that exosomes attracted MSCs, and the fibrin gel enhanced their effect. Moreover, exosomes improved the proliferation of MSCs. Therefore, we propose that pulp-derived exosomes in combination with a fibrin gel could be a powerful combination for clinical translation towards improved cell-free regenerative endodontics and thus represent a new way to fill dental hard tissues.

The addition of Dual Rinse HEDP, an etidronate powder, to a sodium hypochlorite (NaOCl) solution can create a combined single endodontic irrigant with a soft tissue-dissolving and a decalcifying effect, which can replace traditional alternating irrigation with chemically non-compatible solutions. While the short-term compatibility between NaOCl and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) has been shown, it remains unclear whether ultrasonic activation of a combined NaOCl & HEDP solution immediately reduces the available chlorine and/or renders the NaOCl ineffective in dissolving organic tissue remnants. This was tested in three experiments: (1) direct activation in test tubes in an ultrasonic bath and then the activation by an ultrasonically oscillating tip (IrriSafe) in (2) an epoxy resin model containing a simulated isthmus filled with gelatin, and (3) extracted teeth with simulated resorption cavities filled with soft tissue. The control solutions were physiological saline and 2.5% NaOCl without HEDP. In (1), available chlorine after 30 s of ultrasonic activation (37 kHz) of test and control solution was assessed, as well as shrimp tissue weight loss in direct exposure. In (2) and (3), the ultrasonic tip was driven at 1/3 of full power using the respective unit, and areas of removed gelatin from the isthmus and tissue weight loss were used as the outcomes, respectively. Experiment (1) revealed no negative impact by HEDP on available chlorine (1), while all three experiments showed a highly significant (p > 0.001) synergistic effect, which was not hampered by HEDP, between NaOCl and ultrasonic activation regarding tissue weight loss (1, 3) and dissolution of gelatin (2).