Tissue Responses of Human Dental Pulps to Mineral Trioxide Aggregate

Objectives: Mineral trioxide aggregate (MTA) is known to induce hard-tissue repair when used for direct pulp capping. The aim of this study was to investigate the reparative process of human dental pulps capped with MTA. Methods: Pulp exposures were performed on the occlusal floor of premolars and third molars. After that, the pulp was capped with MTA (ProRoot White MTA, Dentsply) and restored with composite resin. At 7, 10, 14, 28, and 56 days after pulp capping, the teeth were extracted and processed for immunohistochemical analysis. Immunoperoxidase staining was performed using antibodies against bone sialoprotein (BSP), osteopontin (OPN), nestin (an intermediate filament expressed in differentiating and functional odontoblasts), and Ki-67. Results: Proliferating cells labeled with Ki-67 were detected between 7 and 28 days and peaked at 10 days. These cells were predominantly distributed beneath the exposure site and around the blood vessels. At 14 days, BSP-immuoreactivity was found at the interface between MTA and the pulp, where nestin-immunopositive cells aggregated. At 28 days, matrix formation had started along the BSP-immunopositive layer that was lined with nestin-positive cells. At 56 days, the hard-tissue barrier was thickened and pulpally lined with elongated odontoblast-like cells that expressed nestin in their cell bodies and processes. The superficial layer of the barrier was immunoreactive for BSP, followed by irregular fibrous matrix and dentin-like matrix with tubular structures. OPN-immunoreactivity was detected in the fibrous matrix, but not for dentin-like matrix. Conclusions: These results suggest that non-collagenous proteins, such as BSP and OPN may be involved in migration of progenitors and their differentiation into odontoblast-like cells during reparative dentinogenesis after pulp capping. Supported by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Sciences.