Bismuth Oxide
Although bismuth oxide is believed to be chemically inert, it is a known catalyst for the oxidation of various organic compounds.22
As it is believed to be chemically inert, it should not chemically bond with any particles within the hydration of MTA and therefore the bismuth oxide particles should remain unchanged and maintain the same particle. Research has illustrated that bismuth is present as unreacted filler in hydrated MTA as well as forming part of the structure of the calcium-silicate-hydrate. 10 Although Camilleri10 hypothesises that the bismuth oxide reacted with the calcium-silicate-hydrate, it is possible that the bismuth oxide was attracted to the structures by van der Waals forces and physical caught within the crystalline structure, rather than forming chemical bonds. As this study involves atmospheric moisture, the calcium-silicate-hydrate structures in the MTA are less likely to entrap the bismuth oxide as the hydration occurs mainly on the most superficial powder, rather than throughout all of the powder as seen during mixing with mixing water, and therefore, the bismuth oxide particles are not expected to be significantly incorporated within the hydration structures.
10. Camilleri J. Hydration mechanisms of mineral trioxide aggregate. Int Endod J 2007;40:462-470.
22. Leonard NM, Wieland LC, Mohan RS. Applications of bismuth (III) compounds in organic synthesis. Tetrahedron 2002;58:8373-8397.