Cross-talk among odontoblasts, dental pulp stem cells, and immune cells after exogenous injuries

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Using an in vivo model for tooth replantation in mice, we have assessed the effects of two types of synthetic CpG ODNs solutions: Type A (D35, MW:6327.33) and Type B (K3, MW:6349.37) on the healing process of the afflicted dental pulp. The penetration of these solutions in the pulpal tissue was confirmed by using an FITC-conjugated-CpG ODN solution one hour after replantation and 24 hours after replantation without variations on its intensity. For the assessment of the most suitable condition, we tested three different concentrations: 10 mg/ml (1.57 mM), 0.63 mg/ml (0.1 mM) and 5 mg / ml (0.8 mM) for each type of CpG ODN solution. Quantitative analysis of Nestin immunohistochemistry showed that 0.1 mM Type-A and -B CpG ODNs solutions favored the healing of the pulpal tissue two weeks after operation, specially Type B. Conversely, the 1.25 mM of both CpG ODNs induced the highest rate of Nestin-negative hard tissue areas in the dental pulp, suggesting an increase in bone-like tissue formation. The treatment with low-concentration CpG-ODNs solution drastically reduced the rate of proliferative cells in the dental pulp, which is reverted at Week 2, when compared to control groups. Preliminary in vitro data obtained from pulp samples following tooth replantation showed that odontoblast differentiation (Nestin mRNA) is sustainedly induced by CpG ODN type B from days 1-5. Bone-related marker (Osteocalcin mRNA) also increased its expression at day 3 following replantation.