Early hydration of white Portland cement in the presence of bismuth oxide

Mineral trioxide aggregate (MTA) is a clinical product comprising a mixture of 80 wt-% Portland cement and 20 wt-% bismuth oxide, which is used as a root-filling material in dentistry. The influence of bismuth oxide on the hydration reactions of Portland cements is not well understood. In this study, the impact of 20 wt-% replacement of bismuth oxide on the hydration of white Portland cement was monitored by powder X-ray diffraction (XRD), Si-29 and Al-27 magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) and transmission electron microscopy (TEM). The findings of this research have confirmed that bismuth oxide is an inert additive in white Portland cement, which does not participate in the hydration reactions.