Reactivity and Environmental Factors

Abstract

Hydrated mineral trioxide aggregate (MTA) is composed of un-hydrated cement particles, which acts as a core around which a reaction rim of hydration products is formed ( Fig. 2.5 ). When mixed with water, the tricalcium and dicalcium silicate react forming calcium silicate hydrate (honeycomb appearance) and calcium hydroxide (hexagonal plates) (Fig. 2.6 ), which is leached in solution. The presence of calcium hydroxide has been verifi ed by X-ray diffraction analysis as it produces a typical peak for portlandite at 18° 2 θ (Fig. 2.9 ), whilst the leaching of calcium has been measured by inductively coupled plasma. The particular microstructure of MTA and the presence of calcium hydroxide in solution make the material susceptible to environmental factors. The use of MTA brings it into contact with other materials, tissues and fl uids, and a number of changes occur within or on the surface of the material in various environmental conditions. Effect of Environmental Factors on the Set MaterialMTA has a variety of applications mostly in Endodontics. These various uses have been discussed [ 60 ] and are outlined in Chap. 6 . Dental Materials Glass IonomerCovering MTA with glass ionomer cement when it is used as a pulp capping agent results in physical changes to the materials at their interface ( Fig. 5.1a ). A sizable gap has been observed at the interface attributed to the movement of water out of MTA into the glass ionomer. This movement of water out of MTA can inhibit its hydration and increases its porosity [ 9 ]. There is no evidence that covering MTA with a glass ionomer has an effect on the glass ionomer cement itself with regard to setting time and setting reaction [ 5 , 36 ]. However, migration of strontium from glass ionomer to MTA has been observed [ 9 ], although its effects are unknown. Base MaterialsZinc oxide eugenol-based cements are used as temporary fi lling materials and come into contact with MTA when it is used for pulp capping. Zinc is a retarder of cement hydration [ 47 ], and zinc salts form calcium hydrozincate (Ca(Zn(OH) 3 H 2 O) 2 ), an insoluble hydroxide in alkaline solution that creates a coating on MTA particles. In addition, zinc

Leaching and cytotoxicity of bismuth oxide in ProRoot MTA – A laboratory investigation

“…It is composed of Portland cement with bismuth oxide added as the radiopacifier (Camilleri et al, 2005(Camilleri et al, , 2013 to enable radiographic detection of the material when used clinically (Húngaro Duarte et al, 2009). Hydraulic calcium silicates form calcium hydroxide on setting (Camilleri, 2007(Camilleri, , 2008(Camilleri, , 2020 which is responsible for the increased alkalinity (Duarte et al, 2003) and material interaction with the surrounding clinical environment (Camilleri and Dummer, 2014).…”