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.