Reactivity and Environmental Factors
Hydrated mineral trioxide aggregate (MTA) is composed of calcium silicate hydrate, calcium hydroxide, ettringite, monosulphate and bismuth oxide together with unreacted tricalcium and dicalcium silicate. The presence of calcium hydroxide, which is usually
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Reactivity and Environmental Factors Josette Camilleri and Paul Dummer
5.1
Introduction
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 verified by X-ray diffraction analysis as it produces a typical peak for portlandite at 18° 2θ (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 fluids, and a number of changes occur within or on the surface of the material in various environmental conditions.
J. Camilleri, BChD, MPhil, PhD, FIMMM, FADM (*) Department of Restorative Dentistry, Faculty of Dental Surgery, Medical School, Mater Dei Hospital, University of Malta, Msida, MSD 2090, Malta e-mail: [email protected] P. Dummer, BDS, MScD, PhD, DDSc, FDSRCS(Ed) School of Dentistry, College of Biomedical and Life Sciences, Cardiff University, Heath Park, Cardiff CF14 4XY, Wales, UK e-mail: [email protected]
5.2
Effect of Environmental Factors on the Set Material
MTA has a variety of applications mostly in Endodontics. These various uses have been discussed [60] and are outlined in Chap. 6.
5.2.1
Dental Materials
5.2.1.1 Glass Ionomer Covering 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.
5.2.1.2 Base Materials Zinc oxide eugenol-based cements are used as temporary filling 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)3H2O)2), an insoluble hydroxide in alkaline solution that creates a coating on MTA particles. In addition, zinc
J. Camilleri (ed.), Mineral Trioxide Aggregate in Dentistry, DOI 10.1007/978-3-642-55157-4_5, © Springer-Verlag Berlin Heidelberg 2014
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a
b
Fig. 5.1 (a) Interaction of glass ionomer cement with MTA leading to failure of glass ionomer and (b) layering of MTA with zinc oxide eugenol with a resultant
retardation
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