Bioactivity of Mineral Trioxide Aggregate and Mechanism of Action

Abstract

In tissue regeneration research, the term ‘bioactivity’ was initially used to describe the resistance to removal of a biomaterial from host tissues after intraosseous implantation. Mineral trioxide aggregate (MTA) and hydraulic calcium silicate cements (HCSCs) in general have been putatively accepted as bioactive materials, as exemplified by the increasing number of publications reporting that these cements are capable of forming an apatite-rich surface layer after they come into contact with simulated body fluids. The proposed mechanisms responsible for establishing in vitro and in vivo bioactivity in glass-ceramics are used as blueprints for investigating whether bioactivities are identifiable in HCSCs. The literature abounds with evidence that HCSCs exhibit in vitro bioactivity. There is a general lack of stringent methodologies for characterising the calcium phosphate phases precipitated on HCSCs. Nevertheless, the mechanisms responsible for in vitro bioactivity of these cements may be generally described in stages that are analogous to those exhibited by bioactive glasses. Although in vivo bioactivity has been demonstrated for some HCSCs, a fibrous connective tissue layer is frequently seen along the bone–cement interface that is reminiscent of the responses observed in bioinert materials, without accompanying clarifications to account for such observations. As bone bonding is not predictably achieved, there is presently insufficient scientific evidence to substantiate that HCSCs are indeed bioactive. Objective, universally acceptable appraisal criteria should be developed in the future to guide manufacturers and scientists in more accurately defining the bioactivity profiles of novel HCSCs introduced for clinical use.