Reparative Dentinogenesis of Rat Molars Pulp-capped with Mineral Trioxide Aggregate

Objectives: This study aimed to analyze the reparative dentinogenic process following pulp capping with mineral trioxide aggregate (MTA) by immunolocalization of nestin (an intermediate filament expressed in differentiated odontoblasts), osteopontin (a non-collagenous protein involved in matrix mineralization, cell-matrix interaction and cytodifferentiation) and proliferating cells. Methods: Maxillary first molars of 8-week-old rats (n = 20) were mechanically pulp-exposed, pulp-capped with MTA (ProRoot White MTA, Dentsply), and restored with a flowable resin composite (Filtek Flow, 3M ESPE). After 1, 3, 5, 7 and 14 days (n = 4, each), the animals were perfusion-fixed and the teeth were processed for immunohistochemistry. Immunoreactivity for nestin and osteopontin was demonstrated by means of immunoperoxidase staining. Cell proliferation assay by 5-bromo-2'-deoxyuridine (BrdU)-labeling was also carried out. Results: MTA-capping caused mild degenerative changes of the exposure site at 1 day. This was followed by progressive new matrix formation, and calcified bridging was recognized in all specimens at 14 days. Proliferating cells peaked at 3 days when the new matrix formation was still inconspicuous. Nestin-immunopositive cells appeared subjacent to the MTA-pulp interface at 3 days, were arranged beneath the newly-formed fibrous matrix at 5 days and showed odontoblast-like morphology by 14 days. Osteopontin-immunoreactivity was detected just beneath the degenerative area at 1 day, occurred along the outer portion of the newly formed fibrous matrix at 5days, and remained evident along the superficial layer of the newly formed dentin bridge matrix at 14 days. Conclusions: The mechanism of reparative dentinogenesis following MTA-capping may be basically similar to that following calcium hydroxide, since it may involve proliferation and migration of progenitors followed by their differentiation into odontoblast-like cells. Osteopontin might play some triggering role in the initiation of pulpal reparative process. Supported by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Sciences.