Crystallochemical comparison between Portland cements and mineral trioxide aggregate (MTA).

Purpose: The aims of this study were to compare the crystal chemical properties of some commercial mineral trioxide aggregate (MTA) and Portland cements (PC) and to propose a new white MTA product. Methods: The samples (four MTA and two PC types) were analyzed by 1) optical microscopy; 2) laser granulometry; 3) X-ray diffraction and fluorescence; 4) scanning electron microscopy (SEM) and electron probe microanalysis (EPM) (wavelength-dispersive). Results: MTA and PC specimens yielded similar characteristics in their clinker component. The MTA-Angelus specimens displayed a composition overlapping the classical clinker composition (wt%) i.e. 25 silica, nine alumina and 66 lime. However, the bismite, present in large amounts (~15-19 wt%) in all MTA products, contained considerable and diffused heavy (toxic) metals as Pb and Mo, other than Bi. In the MTA clinkers the formation of Portlandite, at water-clinker interface, is favored by the smaller grain size of the MTA particles. However, this may also favor the diffusion of the toxic elements linked to Bi. Significance: In terms of bulk physico-chemical properties, the MTA products can be easily substituted by a fine-grained Portland clinker by adding a non-toxic radio-opaque component, for example, Ba-carbonate. [ABSTRACT FROM AUTHOR]