Reparative dentinogenesis induced by mineral trioxide aggregate: a review from the biological and physicochemical points of view

Abstract

This paper aims to review the biological and physicochemical properties of mineral trioxide aggregate (MTA) with respect to its ability to induce reparative dentinogenesis, which involves complex cellular and molecular events leading to hard-tissue repair by newly differentiated odontoblast-like cells. Compared with that of calcium hydroxide-based materials, MTA is more efficient at inducing reparative dentinogenesis in vivo. The available literature suggests that the action of MTA is attributable to the natural wound healing process of exposed pulps, although MTA can stimulate hard-tissue-forming cells to induce matrix formation and mineralization in vitro. Physicochemical analyses have revealed that MTA not only acts as a "calcium hydroxide-releasing" material, but also interacts with phosphate-containing fluids to form apatite precipitates. MTA also shows better sealing ability and structural stability, but less potent antimicrobial activity compared with that of calcium hydroxide. The clinical outcome of direct pulp capping and pulpotomy with MTA appears quite favorable, although the number of controled prospective studies is still limited. Attempts are being conducted to improve the properties of MTA by the addition of setting accelerators and the development of new calcium silicate-based materials.

Figure 1

Dentin bridge formation in rat molar at 14 days after direct pulp capping with MTA: H-E staining (a), immunohistochemistry of nestin (b), and osteopontin (c). (a) A thin layer of fibrous matrix (arrows) is followed by a dentin-like matrix (∗) with tubular structures pulpally lined with odontoblast-like cells. (b) The odontoblast-like cells intensely express nestin, an intermediate filament expressed in differentiated odontoblasts. Their processes also show immunoreactivity for nestin in the tubular matrix (∗). (c) Osteopontin immunoreactivity is detected in the superficial fibrous matrix (arrows), but not in tubular dentin-like matrix (∗).

Figure 2

SEM photograph of the surface of white MTA immersed in PBS for 10 days, showing precipitates of various morphologies. Wavelength-dispersive X-ray spectroscopy analysis revealed that the precipitates contained Ca and P as their main elemental components.