Bioactivity of Mineral Trioxide Aggregate and Mechanism of Action
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 (H
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Bioactivity of Mineral Trioxide Aggregate and Mechanism of Action Franklin R. Tay
4.1
Introduction
In the grand scheme of things, a bioactive material may be broadly defined as ‘one which has been designed to induce specific biological activity’ [162]. Based on this generic definition, biologically active materials may include those that promote tissue regeneration by adhesion to soft and hard tissues of the human body and those that possess cell-instructive and molecularsignalling properties via functionalised ligands or incorporating growth factors for regulating cell proliferation, migration, differentiation, protein expression and mineralisation processes. Other bioactive materials include those that are designed for biosensing or biological recognition via physicochemical interactions, those that contain recognition sites for cleavage of enzymes involved in cell functions and those that possess antimicrobial or immunoregulatory activities by incorporating antimicrobial agents or molecules that mimic natural host-defence peptides [4, 21, 26, 82, 103]. Along the same line of thought, bioactive materials may also include those that incorporate bioactive peptides with antithrombotic, antihypertensive, opioid or antioxidative properties for controlled release [140].
F.R. Tay, BDSc (Hons), PhD Department of Endodontics, Georgia Regents University College of Dental Medicine, Rm 2270, 1430 John Wesley Gilbert Drive, Augusta 30912, GA, USA e-mail: [email protected]
Prior to the adoption of this contemporary interpretation of bioactivity, scientists in the field of tissue regeneration have been using a more focused definition of ‘bioactivity’ to describe the resistance of a calcium phosphosilicate glass to be removed from the host hard and soft tissues, after it was experimentally implanted in rat femurs and muscles [78]. The phenomenon of interfacial bonding between the implant and living tissues has subsequently been observed in other synthetic calcium phosphate ceramics and silicate-based, boratebased and phosphate-based glasses [79, 115], which form the foundation of the field of biomaterials science known as ‘bioactive glass-ceramics’. A bioactive material, as defined by Hench and coworkers, is one that elicits a specific biological response at the interface of the material, which results in the formation of a bond between living tissues and the material [125]. A feature commonly identified from these materials is a time-dependent kinetic modification of the material’s surface via the formation of a carbonated apatite surface layer following its implantation in vivo [40, 77]. The tissue regeneration definition of bioactivity has undergone a subtle paradigm drift, after the feature of in vivo carbonated apatite formation over an apatite/wollastonite glass-ceramic [86], being one of the stages that contributes to the bone-bonding ability of a bioactive material to living tissues, was found to be reproducible in vitro by immersing the material in a simulated body fluid designed to mimic human blood plas
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