Dr Mohammad Hossein Nekoofar
Immediate Past President of Iranian Association of Endodontists
Director of International Relations, Tehran University of Medical Sciences
Honorary Senior Clinical Lecturer, Cardiff University
The effect of contamination on selected physical and chemical characteristics of Mineral Trioxide Aggregate

The effect of contamination on selected physical and chemical characteristics of Mineral Trioxide Aggregate

Aim: To evaluate the effect of various environmental (clinical) conditions on the physical and chemical characteristics of Mineral Trioxide Aggregate (MTA).
Methodology: Initially preparation of specimens was standardised. Moreover, a novel mixing technique, trituration of encapsulated MTA, was developed. The effects of acid and blood contamination on various characteristics of MTA including compressive strength, surface microhardness, push-out bond strength and total porosity were then evaluated. Furthermore, by using X-ray diffraction analysis the hydration process of blood contaminated MTA was studied. In addition, the microstructure of contaminated MTA specimens was compared with control groups.
Results: Methods of mixing and placing MTA significantly affected the hydration process and consequently the physical properties of the material. The lowest and greatest compressive strength, Vickers surface microhardness, and push-out strength values of MTA were found after exposure to pH levels of 4.4 and 7.4, respectively. In addition, scanning electron microscopy revealed a lack of needle-like crystals when the material was in contact with more acidic solutions. The hydration state of specimens partially mixed with blood was more complete than those mixed entirely with blood and less than specimens that were hydrated only with water.
Conclusion: In experimental investigations, use of controlled mixing and placement techniques when using MTA is essential in order to standardise specimen preparation. Delaying the placement of the final coronal restoration i clinical situations when MTA is contaminated is recommended so that the material can acquire sufficient physical properties to withstand the acid-etch procedure and the condensation pressures that occur during the placement of a restoration and/or produced through indirect masticatory forces.

The full text is available at:  http://orca.cf.ac.uk/14248/
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