Development of Rat Caries-Induced Pulpitis Model for Vital Pulp Therapy.

Rodent animal models for vital pulp therapy are commonly used in dental research because their tooth anatomy and cellular processes are similar to the anatomy and processes in humans. However, most studies have been conducted using uninfected sound teeth, which makes it difficult to adequately assess the inflammatory shift after vital pulp therapy. In the present study, we aimed to establish a caries-induced pulpitis model based on the conventional rat caries model and then evaluate inflammatory changes during the wound-healing process after pulp capping in a model of reversible pulpitis induced by carious infection. To establish the caries-induced pulpitis model, the pulpal inflammatory status was investigated at different stages of caries progression by immunostaining targeted to specific inflammatory biomarkers. Immunohistochemical staining revealed that both Toll-like receptor 2 and proliferating cell nuclear antigen were expressed in moderate and severe caries-stimulated pulp, indicating that an immune reaction occurred at both stages of caries progression. M2 macrophages were predominant in moderate caries-stimulated pulp, whereas M1 macrophages were predominant in the severe caries-stimulated pulp. Pulp capping in teeth with moderate caries (i.e., teeth with reversible pulpitis) led to complete tertiary dentin formation within 28 d after treatment. Impaired wound healing was observed in teeth with severe caries (i.e., teeth with irreversible pulpitis). During the wound-healing process in reversible pulpitis after pulp capping, M2 macrophages were predominant at all time points; their proliferative capacity was upregulated in the early stage of wound healing compared with healthy pulp. In conclusion, we successfully established a caries-induced pulpitis model for studies of vital pulp therapy. M2 macrophages have an important role in the early stages of the wound-healing process in reversible pulpitis.

Novel Functional Peptide for Next-Generation Vital Pulp Therapy.

Although vital pulp therapy should be performed by promoting the wound-healing capacity of dental pulp, existing pulp-capping materials were not developed with a focus on the pulpal repair process. In previous investigations of wound healing in dental pulp, we found that organic dentin matrix components (DMCs) were degraded by matrix metalloproteinase-20, and DMC degradation products containing protein S100A7 (S100A7) and protein S100A8 (S100A8) promoted the pulpal wound-healing process. However, the direct use of recombinant proteins as pulp-capping materials may cause clinical problems or lead to high medical costs. Thus, we hypothesized that functional peptides derived from recombinant proteins could solve the problems associated with direct use of such proteins. In this study, we identified functional peptides derived from the protein S100 family and investigated their effects on dental pulp tissue. We first performed amino acid sequence alignments of protein S100 family members from several mammalian sources, then identified candidate peptides. Next, we used a peptide array method that involved human dental pulp stem cells (hDPSCs) to evaluate the mineralization-inducing ability of each peptide. Our results supported the selection of 4 candidate functional peptides derived from proteins S100A8 and S100A9. Direct pulp-capping experiments in a rat model demonstrated that 1 S100A8-derived peptide induced greater tertiary dentin formation compared with the other peptides. To investigate the mechanism underlying this induction effect, we performed liquid chromatography-tandem mass spectrometry analysis using hDPSCs and the S100A8-derived peptide; the results suggested that this peptide promotes tertiary dentin formation by inhibiting inflammatory responses. In addition, this peptide was located in a hairpin region on the surface of S100A8 and could function by direct interaction with other molecules. In summary, this study demonstrated that a S100A8-derived functional peptide promoted wound healing in dental pulp; our findings provide insights for the development of next-generation biological vital pulp therapies.

Effect of tissue inhibitor of metalloprotease 1 on human pulp cells in vitro and rat pulp tissue in vivo.

AIM: To evaluate the dentinogenetic effects of tissue inhibitor of metalloprotease (TIMP1) on human pulp cells in vitro and rat pulp tissue in vivo. METHODOLOGY: The effect of TIMP1 on pulp cell functions related to hard tissue formation as part of the wound healing process (i.e. biocompatibility, proliferation, differentiation and mineralized nodule formation) was evaluated in vitro and using a direct pulp capping experimental animal model in vivo. The effects of different-sized cavity preparations on hard tissue formation induced by ProRoot MTA at 2 weeks were evaluated using micro-computed tomography (micro-CT). Tertiary dentine formation quality and quantity after pulp capping using TIMP1, ProRoot MTA and phosphate-buffered saline (PBS) was also evaluated after 4 weeks using micro-CT in term of dentine volume (DV), dentine mineral density (DVD) and histological analysis. The data were evaluated by Student's t-test, one-way ANOVA with Tukey's post hoc test, the Kruskal-Wallis test or the Steel-Dwass test. P values < 0.05 were considered statistically significant. RESULTS: TIMP1 significantly stimulated dental pulp stem cell proliferation, differentiation, and mineralization and was more biocompatible compared with the PBS control (P < 0.05). In the pulp capping model, the amount of tertiary dentine that formed was directly proportional to the size of the pulp exposure; greater amounts of tertiary dentine were observed in pulps with larger exposures after 2 weeks. 4-week samples of TIMP1 and ProRoot MTA had similar characteristics, but both sample significantly induced tertiary dentine formation beneath the cavity compared with PBS (P <  0.05) under standardized cavity preparations. CONCLUSIONS: TIMP1 has an important role in pulpal wound healing, which makes it a potential biological pulp capping material and candidate molecule for regenerative endodontic therapy.