Immunohistochemical Analysis of Nestin, Osteopontin, and Proliferating Cells in the Reparative Process of Exposed Dental Pulp Capped with Mineral Trioxide Aggregate

This study investigated the reparative process of mechanically exposed pulps capped with mineral trioxide aggregate (MTA). Maxillary first molars of 8-week-old rats were MTA-capped for 1–14 days, and 5-bromo-2′-deoxyuridine–labeled proliferating cells and immunoreactivity for nestin and osteopontin were analyzed. MTA capping caused mild necrotic changes followed by progressive new matrix formation and calcified bridging. Proliferating cells peaked at 3 days when matrix formation was inconspicuous. Nestin-expressing cells appeared at 3 days, were arranged beneath the newly formed matrix at 5 days, and showed odontoblast-like morphology by 14 days. Osteopontin immunoreactivity was detected just beneath the necrotic area after 1 day. These findings suggest that pulpal responses to MTA capping involve proliferation and migration of progenitors followed by their differentiation into odontoblast-like cells, a mechanism basically similar to those to calcium hydroxide. Osteopontin might play a triggering role in initiation of the pulpal reparative process.