Mineral trioxide aggregate (MTA) is an alternative endodontic material that predicts conductive or inductive calcified tissue formation from immature pulp mesenchymal stem cells (IPMSCs). The purpose of this study was to investigate whether MTA could promote reparative odontoblast differentiation via IPMSCs in the early phase of regeneration and compare with calcium hydroxide (CH). Direct pulp capping using calcium hydroxide (CH), MTA, and MTA with platelet-rich plasma (MTA + PRP) was performed on maxillary first molars of 8-week-old male Wistar rats (n = 36). After 3, 7, or 14 days, the teeth were analyzed for mineral density (MD) and volume of MD (VMD) via micro-focusing computed tomography (µCT), nestin, dentin matrix acidic phosphoprotein 1 (DMP1) immunohistochemistry, and real-time PCR for DMP1 mRNA expression. MTA stimulated the early phase differentiation of the IPMSCs into odontoblasts, with positive results for nestin and DMP1 compared with CH. Moreover, MTA + PRP stimulated calcified granule and dentin bridge formation through calcium mineral deposition, following the induction of DMP1 mRNA expression in IPMSCs. Our results suggested that the combination of MTA and PRP is an effective and clinically applicable method for activating endogenous dental pulp stem cells into odontoblasts in the early stages of pulp regeneration.

Dens invaginatus (DI) is one of the rare developmental tooth anomaly, and generally resulting from invagination of the inner enamel epithelium into the dental papilla before calcification. However, it remains unclear whether the invaginated enamel mineralizaion is lower than outer enamel, the association with the resistance to invaginated enamel caries and the inflammatory lesions mediated their invagination. Because of the difficulties of treating and the tendency of their inflammatory lesions mediated their malformed structures, teeth extracted from the patients with DI, were collected in our hospital and analyzed by three-dimensional micro-focusing computed tomography (µCT) to clarify the differences of the invaginated enamel in mineral density (MD), and to find their pathogenesis of tooth anomaly and associated inflammatory lesions by histological analysis. The teeth were fixed with 10% formaldehyde and analyzed by µCT, decalcified specimens were performed to histological (HE) and immunohistochemistry for cytokeratin AE1/AE3. All invaginated teeth enamel showed extremely lower MD than did the outer enamel. Interestingly there were no carious lesions in the invaginated enamel. HE showed thin reduced enamel epithelium on the surface of invaginated enamel and cytokeratin AE1/AE3 markedly showed positive their cellular matrix. The persistent reduced enamel epithelium of the invaginated enamel indicates delayed or inhibited maturation after tooth eruption. This failure of maturation results in lower MD but resistance to enamel caries. However, the structural abnormalities of DI teeth may allow bacteria to enter the interior of the tooth through the invagination, causing pulpitis or apical periodontitis. (243 words)