## 5 Application of DDM in Tooth Regeneration  
Besides bone regeneration, DDM has also been investigated for tooth regeneration applications [54; 55; 10; 56]. The bioactive molecules in the dentin matrix participate in naturally regenerative dentin formation in cases of trauma and infection. Indeed, the bioactive molecules from DDM can influence the survival, apoptosis and differentiation of human dental pulp stem cells (hDPSCs) [54]. DDM extracts were found to promote hDPSC expansion, decrease apoptotic markers expression, stimulate cell survival markers expression, and promote mineral synthesis and osteogenic related genes expression [54]. DDM was also effective in inducing odontogenic differentiation in hDPSCs. The odontogenically-related genes includingDMP1 and DSPP were found to be upregulated [55]. Another study compared the osteogenic induction and odontogenic induction of DDM with HA/TCP on hDPSCs, and found that DDM and HA/TCP had similar efficiencies in bone formation in the dorsum of immunodeficiency mice, while DDM induced greater dentinogenic differentiation [57]. Therefore, DDM had biological effects on DPSCs and could orchestrate dental tissue repairs. In addition, [PERSON] et al. studied the dentin matrix using another approach [50]. Different pH of phosphoric acid and EDTA were employed to solubilize bioactive molecules from the powdered dentin matrix. They collected the demineralized solution and named it dentin matrix components (DMC). Two different pulp cell populations were treated with different concentrations of DMC (0.01, 0.1, 1.0 and 10.0 \(\upmu\)g/mL). Their results showed that DMC could promote cell proliferation and mineralization, and the 10 \(\upmu\)g/mL concentration had the greatest mineralization among all the tested groups [50]. [PERSON] et al. developed a novel pulp capping agent using TDM [10]. The TDM powder and aqueous TDM extract were prepared, and then they were mixed to form the TDM paste as the pulp capping agent. Calcium hydroxide was used as control. The TDM paste showed more odontogenic gene expression in vitro than calcium hydroxide. In the pulp exposure model in swine, TDM showed better biocompatibility, thicker and more dense dentin bridge formation, and less angiectasis in the pulp under the dentin bridge, compared to calcium hydroxide (Figure 3) [10]. These results showed that the TDM paste could be a promising pulp capping agent. Another study used cryopreserved dentin matrix (CDM) as a scaffold material for dentin-pulp tissue regeneration. CDM was implanted into the dorsum of immunodeficient mice. The results showed that CDM combined with dental follicle cells could form dentin-pulp like tissues which were positive for DSPP, DMP-1, tubulin, and collagen-1. The dentin-pulp-like tissues included pre-dentin, dental tubules, collagen fibers, blood vessels and nerves [58]. In another study, DDM was combined with dental follicle cells and implanted in a mouse model for 8 weeks, where the TDM induced complete dentin tissues [16]. Therefore,TDM was an excellent biomaterial for dentin regeneration. Inspired by the fact that the EDTA-treated dentin matrix could release considerable bioactive molecules, the notion of DDM was introduced into revascularization treatments [59]. Two young patients with necrotic immature permanent teeth were chosen for the revascularization treatment. After appropriate disinfection of the root canal system, different concentrations of EDTA were used to treat root canal dentin walls. Then, bleeding was induced in root canals, and calcium-enriched mixture cement was placed over the blood clots. In all follow-up periods (6 and 12 months), both cases were asymptomatic, and the radiographic findings showed a continued root development [59]. The modification in revascularization through the DDM protocol appeared to be better than the traditional therapy.