Before mixing MTA

Storage of MTA

Portland cement which is stored in an unsealed container with react with atmospheric moisture and result in hydration of the cement. A similar reaction is anticipated with MTA that is left unsealed in its packaging. ProRoot MTA is available in satchels while MTA Angelus is available in jars. Both variants of MTA provide information for storage, some of which using symbols, which may not be immediately clear to the clinician or assistant and inappropriate storage of MTA will result in changes to its properties and therefore may result in unexpected changes in performance of the MTA.

Preparing the tooth for MTA

Acids decompose the products of hydration, both the calcium silicate hydrate structures and calcium hydroxide. They may form new compounds, which, if soluble, may leach out of the structure or, alternatively if the new compounds are not soluble, they may disrupt the cement structure.11

Furthermore, if there is a substantial amount of acid producing bacteria and fungi near the cement, the cement will continue to undergo biodegradation from reactions described above.12

In clinical dentistry, there are multiple scenarios where an acidic environment may be present. Teeth that have undergone any form of endodontic disease, such as pulpititis, necrosis, or apical periodontitis will have acids present from the metabolic wastes produced by bacteria as well as the acidic nature of the inflammatory response.13 In clinical dentistry, there is a decision required to determine whether an interim dressing of calcium hydroxide to neutralise the acid will outweigh the risk that the tooth will have a poorer prognosis by delaying the placement of the final restoration.

It is important to ensure that acidic irrigants, etchants or conditioners have been adequately washed out prior to MTA placement. The use of sodium hypochlorite to wash the tooth structures is worthwhile may neutralize any remaining acid.23

To minimise the influence of irrigants on MTA, the preparation should undergo a final wash with sterile, distilled water before the placement of MTA.24

There are two methodologies to consider when haemorrhage may be sufficient to dislodge the placement of MTA.

The first revolve around methods to encourage haemostasis, from the use of vasoconstrictor-containing anaesthetics, to the use of haemostastic agents. This is particularly relevant in endodontic surgery, particularly apicoectomy, where it would be unfavourable to have to have a second surgical procedure.

The second involves the use dressing the tooth with calcium hydroxide to wait until haemostasis has been achieved prior to the placement of the MTA and permanent restoration. 28 This is particularly applicable in clinical scenarios such as apexification or endodontic preparation of teeth with irreversible pulpitis where significant haemorrhage may be occurring.

Endodontic dressings

It has been suggested that a calcium hydroxide pre-treatment might adversely affect white MTA sealing ability as it may act as an obstacle to MTA’s adaptation to the root canal walls or may become involved in the setting reaction of MTA.14 This may seem at odds with the literature from the construction industry which advocate the use of calcium hydroxide. The fact that the calcium hydroxide dressings used in dentistry contain various additives suggests it could actually be the additives that is interfering with the setting reaction of the MTA. Such additives include, methylcellulose, Carboxymethylcellulose, which may retard the setting of MTA as polysaccharide structures are known to retard the setting of Portland cement.15, 16 Therefore, if a calcium hydroxide dressing is used, tooth preparation should be adequately irrigated to ensure no remaining dressing is present to prevent contamination of the MTA by retarders.

    Dryness of the Tooth

    If the dentine is substantially dry before MTA placement, water will be diffused from the MTA and into the dentine. If the dentine is saturated prior to MTA placement with excess water within the canals or pulp chamber, the overall mix will be wetter than what was mixed.

    11. Neville AM. Properties of concrete. 5th edn. London: Pearson Education Limited, 2011.

    12. Bisschop J. Concrete corrosion, sulfate attack, salt scaling, and strength reduction. Institute for Building Materials. URL: 'http://www.ifb.ethz.ch/education/master_concrete_science/Lecture_20March2012_HD.pdf'. Accessed 24 July 2012.
    13. Nekoofar MH, Namazikhah MS, Sheykhrezae MS, et al. pH of pus collected from periapical abscesses. Int Endod J 2009;42:534-538.

    14. Stefopoulos S, Tsatsas DV, Kerezoudis NP, Eliades G. Comparative in vitro study of the sealing efficiency of white vs grey ProRoot mineral trioxide aggregate formulas as apical barriers. Dent Traumatol 2008;24:207-213.

    15. Cheung J, Jeknavorian A, Roberts L, Silva D. Impact of admixtures on the hydration kinetics of Portland cement. Cement and concrete research 2011;
    16. Peschard A, Govin A, Grosseau P, Guilhot B, Guyonnet R. Effect of polysaccharides on the hydration of cement paste at early ages. Cement and concrete research 2004;34:2153-2158.

    23. Zehnder M. Root canal irrigants. J Endod 2006;32:389-398.
    24. Aggarwal V, Jain A, Kabi D. In vitro evaluation of effect of various endodontic solutions on selected physical properties of white mineral trioxide aggregate. Aust Endod J 2011;37:61-64.
    28. Bogen G, Kuttler S. Mineral trioxide aggregate obturation: a review and case series. J Endod 2009;35:777-790.