Microstructure and chemical analysis of blood-contaminated mineral trioxide aggregate M. H. Nekoofar 1,2 , T. E. Davies 3 , D. Stone 1 , F. B. Basturk 4 & P. M. H. Dummer 1 1 Endodontology Research Group, School of Dentistry, Cardiff University, Cardiff, UK; 2 Faculty of Dentistry, Department of Endodontics, Tehran University of Medical Sciences, Tehran, Iran; 3 School of Chemistry, Cardiff University, Cardiff, UK; and 4 Faculty of Dentistry, Department of Conservative Dentistry and Endodontology, Marmara University, Istanbul, Turkey Abstract Nekoofar MH, Davies TE, Stone D, Basturk FB, Dummer PMH. Microstructure and chemical analysis of blood-contam- inated MTA. International Endodontic Journal, 44, 1011–1018, 2011. Aim To test the hypothesis that blood contamination has a detrimental effect on the chemical properties of Mineral trioxide aggregate (MTA). Methodology The effects of whole, fresh human blood on the microstructure and elemental chemistry of MTA were evaluated using scanning electron microscopy and energy-dispersive X-ray analysis, respectively. The phase compositions of contaminated and uncontaminated MTA were also analysed using X-ray diffraction analysis. Results The hydration state of specimens partially mixed with blood were more complete than those mixed entirely with blood and less than those entirely mixed with water. Acicular crystals, characteristic of ettringite, were abundant in specimens mixed entirely with water and absent from specimens mixed partially or entirely with blood. Calcium hydroxide crystals were absent in specimens contaminated entirely with blood and the unhydrated MTA powder, but present in the other groups. Conclusion Mixing MTA with blood resulted in the lack of formation of the crystalline calcium hydroxide in the early stage of the hydration process. Keywords: energy-dispersive X-ray, Mineral Trioxide Aggregate, mineral trioxide aggregate, scanning elec- tron microscopy, X-ray diffraction analysis. Received 8 September 2010; accepted 14 May 2011 Introduction Mineral trioxide aggregate (MTA) is a hydraulic cement which, in contact with water, forms a nonresorbable and dimensionally stable material (De-Deus et al. 2008). MTA is a derivative of Portland cement (Estrela et al. 2000, Camilleri et al. 2005) that is biocompatible (Torabinejad et al. 1995a), capable of close adaptation to dentine (Shokouhinejad et al. 2010) and has anti- bacterial activity (Torabinejad et al. 1995b). MTA has also the ability to induce hard tissue formation when it comes into contact with connective tissue (Shabahang et al. 1999) and is considered as the material of choice in vital pulp therapies (Nakashima & Akamine 2005), for the repair of accidental and/or pathological root perforations (Pitt Ford et al. 1995), as an apical root canal plug in immature teeth with necrotic pulp tissue (Witherspoon & Ham 2001) and as a root-end filling material in endodontic surgery (Torabinejad et al. 1993). In all of these clinical situations, MTA comes into contact with blood (Nekoofar et al. 2010c). Torabinejad et al. (1994) reported that blood con- tamination did not have a significant effect on the sealing properties of MTA, which was subsequently confirmed by Montellano et al. (2006). In contrast, Vanderweele et al. (2006) reported that MTA had significantly less resistance to displacement from blood- contaminated perforation sites and advised removal of blood before its placement. Nekoofar et al. (2010b,c) demonstrated a reduction in the surface microhardness and compressive strength of blood-contaminated MTA and linked these reductions with the impeded forma- tion of acicular crystalline structures. However, the Correspondence: Dr M. H. Nekoofar, School of Dentistry, Cardiff University, Heath Park, Cardiff CF14 4XY, UK (Tel.: +44 (0)29 20742488; fax: +44 (0)2920742479; e-mail: nekoofarmh@cardiff.ac.uk). doi:10.1111/j.1365-2591.2011.01909.x ª 2011 International Endodontic Journal International Endodontic Journal, 44, 1011–1018, 2011 1011